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Resource changes and fishery biology analysis of Coilia nasus in Oujiang River Estuary 2022, 44(3): 257.  Abstract ( 223 )   PDF (1745KB) ( 420 )   Resource changes and fishery biology analysis of Coilia nasus in Oujiang River Estuary CHEN Weifeng1,2, CAI Jihan3, YE Shen1,2, ZHANG Shitian3, NI Yong3, PENG Xin1,2, CHEN Jian3 (1. Zhejiang Mariculture Research Institute, Wenzhou Zhejiang325005, China; 2. Zhejiang Key  Laboratory of Exploitation and Preservation of Coastal Bioresource, Wenzhou Zhejiang325005, China;  3. Wenzhou Aquatic Technology Extension Station, Wenzhou Zhejiang325000, China; 4. East China Sea  Fisheries Research Institute, Chinese Academy of Fishery Sciences, Shanghai200090, China) Abstract: The Oujiang River Estuary (ORE), a critical habitat for fish foraging, breeding and nursery, represents a high productive ecosystem in the northern subtropical of the west Pacific Ocean. However, due to the rapid development of surrounding cities, various seas have been occupied and marine resources have been exploited intensively, with enormous variations of the community structure of fishery resources. The common economic species, including Coilia nasus, have declined significantly, and have been replaced by younger age, lowvalue and miniaturized fish, indicating that the stability of fish community structure has been increasingly damaged. C. nasus is an important economic fish along the coast of China. It is popular among coastal residents because of its good taste and rich nutrition. It has also received widespread attention from the academic society for the decline of resources in recent years. C. nasus belongs to order Clupeiformes, family Engraulidae, and genus Coilia, and is mainly distributed in China, Japan and the Korean Peninsula. The research on C. nasus has mainly focused on the waters of the Yangtze River Estuary (YRE) in recent years, and the research contents include population, resource changes, reproductive characteristics, age identification and so on. There are few studies on Coilia nasus in the ORE. To understand the resources and its changes of Coilia nasus in the ORE, a total of twelve bottom trawling surveys were carried out in the sea from February 2017 to November 2019. The survey range of east longitude was between 121°00′to 121°54′, and north latitude was between 27°45′to 28°06′. The survey ship was “Zheyueyuxiu 00105” with a main power of 202 kW and a tonnage of 128 t. The opening area of the bottom trawling net underwater was about 6 m (width) and 1.5 m (height), the mesh of the bag net was 2.5 cm, the ship was trawling 0.75 hours per station with a speed of 34 nmile·h-1, all the surveys were carried out during the day. The sweeping area method was used to estimate the biomass distribution of C. nasus, and the biological indicators of all samples were measured. The biological parameters of C. nasus was calculated using FiSAT II, and the BevertonHolt model was constructed to evaluate the changes in resources. Results showed that a total of 1 008 C. nasus were collected in 12 bottom trawling surveys from 2017 to 2019. The average biomass in 2017, 2018 and 2019 was 16.06 kg·km-2, 4.22 kg·km-2 and 14.62 kg·km-2 respectively, while the average abundance was 0.82×103 ind·km-2, 0.13 × 103 ind·km-2 and 0.85 ind·km-2, respectively. The body length of C. nasus ranged from 15 mm to 357 mm, and the dominant body length was between 90 mm to 270 mm with a proportion of 84.36%. The body weight of C. nasus ranged from 0.08 g to 195 g, and the dominant body weight was between 0 g to 270 g with a proportion of 86.61%. From March to April, C. nasus of the ORE began to travel upstream into the freshwater area for reproductive migration. After October, when the water temperature in the ORE dropped, C. nasus descended to the sea for overwintering; in February 2019, 98 tails of C. nasus was caught in a single net at DT09 station. The body length ranged from 88 mm to 280 mm, and the body weight ranged from 3.20 g to 76.25 g, which also showed that the sea area was a wintering ground for C. nasus in winter. By analyzing the temperature and salinity of the survey stations where C. nasus appeared, it was found that C. nasus in the ORE area only appeared at the station with the surface salinity below 31‰ and surface water temperature below 25℃.Growth of C. nasus was described using Von Bertalanffy model based on the body length frequency, and the estimated parameters were  l∞=362.25 mm，k=0.440，W∞=158.38g，t0=-0.31a. The Von Bertalanffy’s growth equations of length and weight were as follows: lt=362.25［1-e-0.44(t+0.31)］; Wt=158.38［1-e-0.44(t+0.31)］3.017 8. The lengthconverted catch curve was used to calculate the total mortality coefficient Z, which was found to be 1.33, and the fitted equations were as follows: ln (N/dt) = 6.916-1.33t (R2=0.931). According to the Beverton Holt dynamic model, the growth inflection point age tλ was 2.20a, the corresponding body length was 242 mm, the weight was 47.00 g, and the capture size was 229.4 mm. According to the twodimensional analysis of relative yield / recruit (Y′/R) and exploitation rate(E), it showed the exploitation of C. nasus in ORE: E10=0.720, E50=0.401, Emax=0.803. With the current opencapture body length Lc=229.4 mm, E>0.68, Y'/R first increased and then decreased with the increase of the exploitation rate of C. nasus; when Lc=229.4 mm, E<0.68, Y′/R increased with the exploitation rate. When E increased from the current 0.68 to Emax (0.803), the corresponding Y′/R reached the maximum (Y′/R≈0.103), and when it fell to E50, the corresponding Y′/R dropped to 0.085. From the perspective of the maintenance of relative unit supplementary biomass (B′/R), the current utilization rate of C. nasus was 0.68, and about 20% of biomass resources (B′/R) were maintained; when Emax=0.803, only 11.8 % of biomass resources (B′/R) were kept, and when E50=0.401, about 50% of biomass resources (B′/R) could be kept. Natural mortality coefficient M was estimated using Pauly’s empirical formula and found to be 0.43. Accordingly, the fishing mortality coefficient (F) was equal to 0.90 (F=Z-M=0.90). The exploitation rate of ORE from 2017 to 2019 was assessed by the formula of E=F/Z, and found to be 0.68. In the present study, the results demonstrated that the exploitation rate of C. nasus was greater than the optimum exploitation rate of fish, while lower than the maximum exploitation rate. Namely, the resources of C. nasus in the ORE have been fully utilized. However, reducing the fishing pressure in an appropriate amount can better protect the resources of C. nasus in the ORE. Therefore, proposal for the establishment of a spawning ground reserve in the waters between Xizhou Island and Nanxi River Estuary to protect and restore the resources of C. nasus is made.  Keywords: Coilia nasus; growth parameters;mortality parameters; exploitation rate; Oujiang River Estuary Related Articles | Metrics

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Acoustic assessment of commercially important pelagic fish resources in the central and southern South China Sea in the summer of 2019 based on acoustic research 2022, 44(3): 267.  Abstract ( 173 )   PDF (3231KB) ( 405 )   Acoustic assessment of commercially important pelagic fish resources  in the central and southern South China Sea in the summer  of 2019 based on acoustic research  HOU Yuwei1,2, LIU Shigang2, LI Yuan2 , SONG Puqing2,  CHEN Zongzheng1,2, LIN Longshan2, ZHANG Jing1 (1.Fisheries College, Jimei University, Xiamen Fujian361021, China; 2. Third Institute of Oceanography,  Ministry of Natural Resources, Xiamen Fujian361005,China) Abstract: The South China Sea is one of the most diverse marine areas in the world. Since the 1990s, the fishery resources in the northern offshore areas of the South China Sea have shown a significant trend of decay, and a large amount of offshore fishing pressure has begun to shift to the central and southern South China Sea. The central and southern South China Sea is rich in fishery resources, including Thunnus albacares, Katsuwonus pelamis, Auxis rochei, Decapterus macrosoma and Selar crumenophthalmus, which have large potential for exploitation. Therefore, accurate assessment of fish stocks is of great significance for guiding fishery production and management in the South China Sea. In recent decades, fisheries acoustics has gradually emerged as a method for fisheries resource assessment. With the advantages of being fast, efficient, high sampling rate, short survey time, not destroying biological resources, and providing abundant spatial and temporal data, fisheries acoustics is suitable for the survey of pelagic biological resources and has been widely used in the assessment of pelagic fishery resources. In order to assess the status of fishery resources in the central and southern South China Sea, scientific echosounder was used to investigate and evaluate the fishery resources in the central and southern South China Sea from June to July 2019 (summer). The investigation area was 109°00′117°30′E, 5°30′16°00′N and the acoustics survey area was about 2.45×105 nmile2 with 42 biological sampling stations by light falling net. The time to lure fish with light was 2 h in each station. After each haul, catches were randomly selected on the deck according to the category ratio, all catches were classified and counted, and then the body length (or fork length) and the weight of the catches were measured and recorded. The acoustic data were collected according to the preset survey route by the split beam Simrad EK80 portable scientific echosounder (120 kHz), and the analysis processing was mainly done with Echoview (version 7.1) software.  The fishery resource density was estimated using the echo integration method. Before the acoustic data analysis, sea surface navigation bubbles, false bottom, plankton and machine signals were removed as interference noises. This survey was conducted by two fishing vessels cooperating with each other. Although the completion of the task was ensured to the maximum extent, it was inevitable that some routes would be lost. In order to fully explore the acoustic data and more intuitively and accurately assess the resource in the central and southern South China Sea, the acoustic data of every 20 nmiles were used as an acoustic assessment station in this study. Furthermore, acoustic integration value was assigned according to the catch ratio of the nearest biological sampling station. In order to exclude the influence of surface navigation noise, the starting water layer of data integration was set to be 10 m. The lower limit of data integration was set to be 200 m, taking into account both the habitat depth of the main catch and quality of the acoustic data. Due to the presence of plankton in the survey area, a suitable integration threshold was set to remove the weak scatters such as plankton. Through the test, the integration threshold was set at -80 dB, which could remove the interference of zooplankton to the greatest extent without losing the signal of the target species. Results of survey indicated that, Thunnus albacares, Katsuwonus pelamis, Auxis rochei, Decapterus macrosoma and Selar crumenophthalmus were the dominant fish species in the survey, with occurrence rates of 71.43%，61.90%，30.95%，78.57% and 85.71%, respectively in 42 biological sampling stations. We measured the biological data of the main economic species: the length range of Thunnus albacares was 37276 mm, the average body length was 148.71 mm, the body mass range was 1.2469.6 g, and the average body mass was 93.15 g; the length range of Katsuwonus pelamis was 46479 mm, the average body length was 155.23 mm, the body mass range was 46479 g, and the average body mass was 97.08 g；the body length of Auxis roche ranged from 62314 mm, with a mean body length of 174.10 mm, and body mass ranged from 4.0657.6 g, with a mean body mass of 109.59 g；the body length of Decapterus macrosoma ranged from 20246 mm with a mean body length of 154.78 mm and body mass ranged from 4.0657.6 g with a mean body mass of 80.69 g；the body length of Selar crumenophthalmus ranged from 30206 mm, with a mean body length of 95.86 mm, and the body mass ranged from 0.8131.7 g, with a mean body mass of 19.31 g. The biomass and abundance of five fish species were assessed by combining fishery acoustic data and biological data. Results of the acoustic assessment showed that the biomass of Thunnus albacares, Katsuwonus pelamis, Auxis rochei, Decapterus macrosoma and Selar crumenophthalmus was 2.81×104 t, 3.77×104 , 8.71×104 t, 5.73×104 t, 2.66×104 t and the abundance was 3.78×109 ind., 2.39×109 ind., 8.95×108 ind., 4.95×108 ind., 1.55×109 ind., respectively. Moreover, areas with the highest biomass density of the five fishes species were concentrated in 14°00′16°00′N, 109°00′117°30′E. Compared with historical survey data, the quantity and structure of fishery resources in the South China Sea have changed to some extent. The quantity of economic fish resources decreased to a certain extent, and showed the phenomenon of miniaturization and younger age. It’s worth noting that the biomass of tuna species, including Thunnus albacares, Katsuwonus pelamis, Auxis rochei has decreased significantly. Therefore, appropriate measures should be considered to protect the tuna resources in the South China Sea. In contrast, the biomass of Carangidae species, including Decapterus macrosoma and Selar crumenophthalmus, has not changed significantly, which means that Carangidae species can still be reasonably exploited. Our research can provide a scientific basis for rational development of fishery resources and development of reasonable conservation strategies in the offshore waters of the South China Sea. Keywords: pelagic fishery; acoustic assessment; South China Sea; summer; resource conservation Related Articles | Metrics

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On the relationship of stock recruitment in Pacific Sardina population based on environmental factors 2022, 44(3): 280.  Abstract ( 159 )   PDF (2160KB) ( 409 )   On the relationship of stock recruitment in Pacific Sardina  population based on environmental factors TANG Xin1, ZHANG Xiancheng1, WANG Jintao1，2，3，4，5, CHEN Xinjun1，2，3，4，5 (1.College of Marine Sciences of Shanghai Ocean University, Shanghai201306, China； 2. Key Laboratory of Oceanic Fisheries Exploration, Ministry of Agriculture and Rural Affairs, Shanghai201306, China; 3. National Engineering Research Center for Oceanic Fisheries, Shanghai Ocean University, Shanghai201306, China； 4. Key Laboratory of Sustainable Exploitation of Oceanic Fisheries Resources, Ministry of Education, Shanghai Ocean  University, Shanghai201306, China;5. Scientific Observing and Experimental Station of  Oceanic Fishery Resources, Ministry of Agriculture and Rural Affairs, Shanghai201306) Abstract: Sardina is an economically and ecologically important pelagic species. They are warm water fishes, and only a few of them have lower optimum temperature. They feed mainly on plankton, and their optimum temperature of habitat is about 2030℃. In the Pacific, Sardina with age more than 1 live around the water of Kuroshio current for overwintering and spawning. In summer and autumn, they stay along the coast or migrate to the north with limited distance for growth. For presence of eggs, Sardina spawn from November to June of the following year. The peak of spawning occurs from February to April, and the best temperature for spawning activity of sardines is between 15℃ and 18℃. Previous research suggested that the recruitment of Sardina was very vulnerable to the marine environmental factors of habitat. However, many reasons including human activities, climate change and its induced local environmental variability have intensified the fluctuations in recruitment of sardines in the Pacific Ocean. Understanding and estimation of how those factors affect the spawningrecruitment (SR) relationship of Sardina is beneficial to sustainable utilization and management of the resource. Unfortunately, estimating parameters in SR relationship is one of the tough tasks in fisheries stock assessment. In addition, the SR relationship is greatly blurred by the abovementioned factors, and critical environmental factors are usually incorporated to explore the relationship between the two. Commonly, Ricker model with considering key environmental factors for spawning is a useful tool to derive the SR relationship. For Sardina in the Pacific Ocean, two validated factors, sea surface temperature (SST) on the spawning ground and Pacific decadal oscillation (PDO), are important for spawning and hatch, thus, we assume that SST and PDO can be the potential factors affecting the SR relationships of Sardina. We combine environmental data including SST on Sardina spawning habitat between 142°165° E and 35°40°N (from Columbia University Climate Center, http://iridl.Ldeo.columbia.edu/SOURCES/.IGOSS/.data_products.Html), PDO data ( form Japan Meteorological Agency, http: //www.jma.go.jp/jma/index. Html) from February to April (spawning season for sardine in the Pacific Ocean) and survey data obtained from the 2016 Pacific Fauna Resource Assessment Report to construct multiple models of the SR relationship of Sardina during 1996—2015. Specifically, we assume that SST and PDO  can affect the SR relationship separately and simultaneously, three alternative models (SST_Ricker, PDO_Ricker, and SST_PDO_Ricker) could be established for Sardina during 1996—2015. According to the survey data, the obvious peak and valley happened in spawning biomass and recruitment of Sardina. After 1996, the spawning biomass was decreasing to historical low level with fluctuation, however, the opposite situation of increasing in biomass reached 1.03 million tons in 2014 as the continuous good recruitment biomass of Sardina and the decreased fishing intensity. In addition, the extremely high recruitment was estimated to be 1.86 million tons in 2015.The performance and robustness of models were evaluated by the Akaike information criterion (AIC) values and leaveoneout cross validation, and the model with the lowest AIC value was the optimal model. Results showed that three alternative models were all better than the original Ricker model (without considering the environmental factor), the SST_PDO_Ricker model with the fewer outliers and the lowest AIC value of 49.99 was the final model to describe the SR relationships for the Pacific Sardina. It meant that the synchronous effect of SST and PDO could affect the mechanism of recruitment for Sardina. By examining the environmental coefficient of the optimal model, it was found that SST and PDO in the spawning period had a positive effect on the recruitment quantity of the Pacific Sardina. The SST and PDO on the spawning grounds could significantly reflect the dynamics of recruitment for the Pacific Sardina, and the SST had more influences on the Pacific Sardina compared with PDO. It was more conducive to the occurrence of recruitment when SST was greater of its mean value and rose steadily. Additionally, high PDO value could make a larger increase in recruitment of 2015. Commonly, PDO can be divided into cold and warm phases. When PDO has a warm phase, the surface water of the north American continent is abnormally warm, while the surface temperature of the North Pacific Ocean is abnormally cold, it can lead to an increase in Sardina recruitment. When PDO has a cold phase, the opposite is true. Compared with PDO, SST may have more ability to affect the recruitment of Sardina. When temperatures are relatively high and above average, there is a significant increase in recruitment. The rising of SST occurring in warm phase would produce more suitable habitat for Sardina in the North Pacific Ocean. This is validated by the observation that the number of 0yearold Sardina increassd significantly during warmer years, and the large and mediumsized Sardina are caught at lower surface salinity and temperatures than that of small Sardina in the Pacific Ocean. Each life stage of Sardina (as one of the poikilotherm fishes), such as spawning, hatching, growth is significantly correlated with water temperature positively or negatively. Understanding the effects of climate change induced environmental variability on fish recruitment on interannual and decadal time scales is fundamental to understand fish population dynamics. Our study suggests that the SR relationship incorporating SST and PDO should be considered for Sardina management. Further, other factors such as food sources and the relationship between other species need to be explored for better assessment and utilization of Sardina resource in the Pacific Ocean. Keywords: Sardina; recruitment; Ricker model; environmental factors Related Articles | Metrics

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Genetic diversity of Phascolosoma esculenta base on mitochondrial cytb gene and d-loop region in the southeast coast of China 2022, 44(3): 288.  Abstract ( 152 )   PDF (1237KB) ( 369 )   Genetic diversity of Phascolosoma esculenta base on  mitochondrial cytb gene and d-loop region  in the southeast coast of China XU Ruiwen1,2, CHEN Xinghan1, YU Xiangyong3 (1.Yangjiang Polytechnic, Yangjiang Guangdong529566, China; 2. Fisheries College, Guangdong  Ocean University, Zhanjiang Guangdong524088, China; 3. School of Marine Science,  South China Agricultural University, Guangzhou510642) Abstract: Phascolosoma esculenta belongs to Sipunculoidea (order), Phascolosomalifo (class), Phascolosomatidae (family), Phascolosoma (genus). It is an endemic species of Sipunculoidea in China, which distributes in coastal tidal flats of the southeastern provinces. As one of the marine treasures, Phascolosoma esculenta is rich in protein and has a variety of unsaturated fatty acids and other nutrients. People call it "animal ginseng" and it is a characteristic economic aquatic creature of local residents. In recent years, the development and construction process of the southeast coastal areas of China has been accelerating, and environmental pollution, tidal flat reclamation, and overload harvesting have resulted in the sharp decline of germplasm resources of wild populations of P. esculenta in China, while the market price has been rising year by year. Therefore, the related resource protection, seedling breeding and enhancement has drawn enormous attention to the industry. However, there are few studies on the population genetics of this species. So it is necessary to study the genetic diversity of wild population of Phascolosoma esculenta for the rational development and sustainable utilization. In this study, the cytb and dloop gene sequences of mitochondrial DNA were used as molecular markers to analyze the genetic diversity and genetic structure of a total of 150 samples from five natural populations of P. esculenta in Zhanjiang City, Guangdong Province (ZJ), Yangjiang City, Guangdong Province (YJ), Qinzhou City, Guangxi Province (QZ), Ningde City, Fujian Province (ND), and Wenzhou City, Zhejiang Province (WZ), which can provide corresponding basic information for artificial breeding and nursery of this endemic Phascolosoma species in China, and provide reference data for subsequent studies on the conservation of germplasm resources and sustainable exploitation of P. esculenta. DNA was extracted from the body wall muscle of P. esculenta using a genome extraction test kit, primers were designed based on its published mitochondrial genes and synthesized by a thirdparty company. The mitochondrial cytb and dloop amplification fragments of P. esculenta through electrophoresis tests were selected for purification and sequencing, using a PCR amplification kit for PCR amplification of DNA samples. Sequencing analysis of 150 samples revealed that the cytb and dloop sequences showed small differences in the content of the four bases and all exhibited significantly higher A+T content than C+G content, with significant nucleobases bias, consistent with the published mitochondrial nucleobases characteristics of P. esculenta. In the five geographical groups, 118 and 158 polymorphic loci were detected for cytb and dloop sequences, respectively, defining 62 cytb haplotype types and 79 dloop haplotype types. Haplotypes of both genetic sequences were randomly dispersed among different populations, with some haplotypes common to multiple populations and some haplotypes specific to individual populations. Such a haplotype distribution could be biologically explained as the result of a combination of a recent exogenous genetic invasion event and subsequent genetic divergence in a geographic population. Analysis of genetic diversity parameters based on both cytb and dloop sequences showed high genetic diversity (cytb: 0.871 3-0.963 2; dloop: 0.942 50.981 6) and low level of nucleotide diversity (cytb: 0.032 4870.040 975; dloop: 0.033 247 0.046 151), with a high overall level of genetic diversity. Combined with the results of Tajima’s D statistic and Fu’ Fs neutrality tests, results of this analysis significantly deviated from the neutrality, through which we could infer that the P. esculenta population has recently experienced a rapid population expansion event, it was derived from a small breeding population to a large population in a relatively short period. The topology of the haplotype neighborjoining trees of cytb and dloop sequences of different populations of P. esculenta was simple and did not show a clear geographical genealogical structure; while the analysis of molecular variance (AMOVA) results showed that the intrapopulation genetic variation (cytb: 98.56%; dloop: 98.61%) was significantly higher than that between populations (cytb: 1.44%; dloop: 1.39%), indicating that the genetic variation of P. esculenta among different geographical groups was not obvious and there was no geographical segregation between different geographical groups. The consistency of the two results illustrated the absence of significant genetic differentiation and low genetic differences among the five geographic groups of P. esculenta. In summary:1) Results of the analysis of two different sequences of the five geographic populations of P. esculenta in Zhanjiang City, Guangdong Province (ZJ), Yangjiang City, Guangdong Province (YJ), Qinzhou City, Guangxi Province (QZ), Ningde City, Fujian Province (ND), and Wenzhou City, Zhejiang Province (WZ), showed high levels of genetic diversity and low levels of nucleotide diversity, with a high level of overall genetic diversity. This feature was also reflected in other researchers’ studies on the genetic diversity of P. esculenta from other geographical populations along the southeast coast of China based on mitochondrial CO I and 16S rRNA gene sequences. Because the accumulation of gene diversity can be improved in a short time, but the accumulation of nucleotide variation takes a longer time. 2) Combined with the Tajima’s D statistic and Fu’s Fs neutrality tests, we can suggest that the P. esculenta population has recently undergone a rapid population expansion event; the genetic variation is not significant among different geographic groups, indicating that the five geographic groups of P. esculenta do not have significant genetic differentiation, and the genetic differences are small. The possible causes of this phenomenon are: ① P. esculenta lives in the intertidal zone along the coast with few geographical barriers. In its early life history, trochophore larvae and pelagosphera larvae disperse along the distance with the movement of sea water, resulting in gene exchange between different geographical populations. ② Due to the increasing maturity of artificial breeding technology and the expansion of breeding scale, many farmers purchase seedlings from various places and put them into local farms. However, the phenomenon of breeding population escape caused by the drainage of the farms often occurs, which makes the gene exchange between the geographical populations of P. esculenta frequent; ③ Because of the similar habitat conditions in the intertidal zone of the southeast coastal areas of China, the genetic variation direction of different geographical populations is indirectly affected. In addition, by combining the results of two algorithms of genetic distance, the genetic distance between ND (Ningde, Fujian) population and other populations is the closest, which may be related to the genetic confusion caused by the escape of artificial seedlings from local farms. The sampling point NiuMu Island located in the gulf is one of P. esculenta breeding bases in Changchun Village, Xiapu County of Mindong region. While the larvae of this species can not satisfy the requirement of aquaculture farmers, they will purchase a large number of larvae for breeding from Guangxi, Zhejiang provinces and other places. Due to the influence of tide, there must be escape in larvae of artificial breeding. This results in severe genetic confusion among local wild geographic populations.  Keywords: Phascolosoma esculenta; genetic diversity; cytb; dloop  Related Articles | Metrics

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Composition and utilization of fatty acids during the endogenous nutrient stage of Alosa sapidissima 2022, 44(3): 303.  Abstract ( 134 )   PDF (742KB) ( 354 )   Composition and utilization of fatty acids during the  endogenous nutrient stage of Alosa sapidissima SHI Yonghai, XU Jiabo, YAN Yinlong, ZHANG Zhiwen, LIU Yongshi,  YU Aiqing, DENG Pingping, JIANG Fei, YUAN Xincheng （Shanghai Fisheries Research Institute, Shanghai Fisheries Technical Extension Station, Shanghai200433, China) Abstract: In order to understand the fatty acids composition, changes and utilization rules during the endogenous nutrient stage of American shad A. sapidissima, biochemical analysis methods were used to detect and analyze the crude fat content and fatty acids composition of A. sapidissima in different developmental stages: embryos during the gastrula stage, newly hatched larvae 0dayage, and before feeding larvae 4dayage. Results showed that the individual crude fat contents of A. sapidissima during the endogenous nutrient stage were high (41.91 μg60.04 μg), the larvae consumed 30.20% of the crude fat before feeding; with the individual development, the moisture content reduced significantly (P<0.05)(the value from 96.42% to 88.25%), the crude fat content of dry matter increased slightly (P>0.05) (the value from 16.33% to 19.13%), the crude fat content of fresh quality increased significantly (P<0.05)(the value from 0.58% to 2.25%), the individual crude fat contents decreased significantly (P<0.05) (the value from 60.04 μg to 41.91 μg) during the endogenous nutrient stage. The top 4 fatty acids relative content was C16∶0 (21.65%23.06%), C18∶1n9c (19.02%20.93%), C22∶6n3 (DHA) (15.02%18.20%), and C18∶2n6c (12.33%14.43%) during the endogenous nutrient stage of A. sapidissima. The C16∶0 relative content of 0dayage larvae was significantly higher than that of embryos and 4dayage larvae (P<0.05), while there was no significant difference between embryos and 4dayage (P>0.05); the relative contents of C18∶1n9c and C18∶2n6c significantly decreased with the individual development (P<0.05); the relative contents of C22∶6n3(DHA) significantly increased (P<0.05) with the development of ontogeny, the C22∶6n3(DHA) relative content of 4dayage larvae was significantly higher than that of embryos and 0dayage larvae (P<0.05), while there was no significant difference between embryos and 0dayage (P>0.05). Although the relative content of C20∶5n3 (EPA) was not high (1.05%1.49%), the relative content of C20∶5n3 (EPA) significantly increased with the individual development (P<0.05). This also resulted in a significant upward trend of DHA+EPA with the individual development (P<0.05), DHA+EPA relative content of 4dayage larvae (19.69%) was significantly higher than that of embryos (16.07%) and 0dayage larvae (16.63%)(P< 0.05), while there was no significant difference between embryos and 0dayage larvae (P>0.05). The SFA relative content of embryos (32.39%) was significantly lower than that of 4dayage larvae (33.53%) (P<0.05), while there was no significant difference between 0dayage larvae and embryos or 4dayage larvae (P>0.05). The relative content of MUFA was relatively low (20.92%22.82%) and significantly decreased with the individual development (P<0.05). The relative content of PUFA was rich and stable (44.76%45.55%), and there was no significant change in the PUFA content among embryos, 0dayage and 4dayage larvae (P<0.05). The ratio of ∑SFA to ∑UFA of 4dayage larvae (0.50) was significantly higher than that of embryo (0.48) (P<0.05). The ratio of ∑n3PUFA to ∑n6PUFA increased significantly with individual growth and development  (P<0.05), and the value increased from 0.69 to 0.94, the ratio of ∑n3PUFA to ∑n6PUFA of embryos and 0dayage larvae was significantly lower than that of 4dayage larvae (P<0.05), while there was no significant difference between embryo and 0dayage larvae (P>0.05).The top 4 fatty acids absolute content in individual was C16∶0, C18∶1n9c, C22∶6n3(DHA) and C18∶2n6c during the endogenous nutrient stage of A. sapidissima. With the individual development and the shedding of egg membrane, the absolute content of C24∶1n9 decreased slightly at first (P>0.05) and then increased significantly (P<0.05), and the absolute content of C15∶0 showed a significant trend of first decrease and later increase (P<0.05), the absolute content of C17∶1 increased slightly at first (P>0.05) and then decreased significantly (P<0.05), the absolute contents of C17∶0, C20∶0, C20∶4n6, C20∶5n3 (EPA) and C22∶6n3 (DHA) had no significant changes (P>0.05), the absolute contents of the other 14 fatty acids in individual showed a significant downward trend (P<0.05). The superposition effect of the decrease of most fatty acids resulted in a significant decreasing trend of absolute contents of the SFA, MUFA and PUFA in individual with individual development (P<0.05). In addition, the absolute contents of EPA+DHA and ∑n3PUFA showed no significant change with the individual development (P>0.05), while the absolute content of ∑n6PUFA showed a significant downward trend (P<0.05). During the embryo incubation period of A. sapidissima, C18∶1n9c (256.31 μg and 20.40%, respectively) and DHA (132.23 μg and 14.64%, respectively) reduced largely. From the point of utilization amount and rate, after the larvae emerged from the membrane to the opening before feeding, there was a certain priority in the use of fatty acids： n6PUFA (295.41 μg and 23.81  %, respectively) >MUFA (224.72 μg and 20.37%, respectively) > SFA (279.79 μg and 16.59%, respectively) > n3PUFA (38.67 μg and 4.19 %, respectively), especially C18∶2n6c (207.48 μg and 28.64 %, respectively) and C18∶3n6 (48.77 μg and 26.53 %, respectively) in n6PUFA, C16∶0 (256.35 μg and 22.02 %, respectively) in SFA and C18∶1n9c (201.86 μg and 20.18 %, respectively) in MUFA were used in priority. While the utilization amount and rate of n3PUFA were extremely low (38.67 μg and 4.19%, respectively)，especially EPA+DHA (18.26 μg and 2.17%, respectively). Researches showed that the EPA was preserved in priority but DHA was used largely during A. sapidissima embryo incubation period; n3PUFA (especially EPA+DHA) was preserved in priority after the larvae emerged from the membrane. ∑n3PUFA/∑n6PUFA was lower (0.690.94) during the endogenous nutrient stage of A. sapidissima, and this showed the fatty acids characteristic of freshwater fish. In the antepartum cultivation and spawning period of brood stock, it is suggested to supplement diets enriched with n3PUFA (especially DHA) in time in parents bodies to enhance the nutrition accumulation and increase the nutrient reserve of the fertilized egg, and then to improve the survival rate of A. sapidissima larvae before feeding. Keywords: Alosa sapidissima; endogenous nutrient stage; embryo; larvae; fatty acids Related Articles | Metrics

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Effects of low salinity on osmoregulation, Na+/K+-ATPase activity and related gene expression of juvenile Epinephelus fuscoguttatus 2022, 44(3): 315.  Abstract ( 200 )   PDF (2161KB) ( 419 )   Effects of low salinity on osmoregulation,  Na+/K+ -ATPase activity and related gene  expression of juvenile Epinephelus fuscoguttatus LIU Longlong1,2, LUO Ming1,2, CHEN Fuxiao1,2, LIU Jinye1,2 ( 1. Key Laboratory of Utilization and Conservation for Tropical Marine Bioresources,  Ministry of Education, Hainan Tropical Ocean University, Sanya572022, China;  2. Hainan Academy of Ocean and Fisheries Sciences, Haikou571126, China ) Abstract: Brownmarbled grouper Epinephelus fuscoguttatus is a popularly important species in tropical mariculture due to its delicious meat, fast growth and strong disease resistance, and has been widely cultivated in Fujian, Guangdong, Hainan and other places. Salinity is an important environmental factor that affects the growth, development and reproduction of fish. Euryhaline teleosts can maintain the stability of internal environment homeostasis through effective osmotic regulation to adapt to the changes of salinity in their living environment. Epinephelus fuscoguttatus has a wide range of salinity tolerance and has been reported that can live in waters with salinity ranging from 11 ‰ to 41 ‰, but little is known about its salinity adaptation mechanism. In order to study the effect of low salinity on osmoregulation of juvenile Epinephelus fuscoguttatus, juveniles with an average weight of (56.8 ± 3.5) g temporarily reared in natural seawater ( 32 ‰ ), were transferred into the water with salinity of 6 ‰, 12 ‰, 24 ‰ and 32 ‰ (control group) for 10 d. Serum osmolality, the concentration of Na+, Cl-, K+ in serum, muscle water content, the Na+/K+ATPase activity and the expressions of NKA α1, NKA β1b, NKA α2a, NKA α3 in gill were determined, and changes of gill microstructure and oxygen consumption rate were observed at the end of the experiment. Results showed that with the decrease of salinity, serum osmolality of juvenile Epinephelus fuscoguttatus decreased, and the serum osmolality of salinity 6 ‰ group was significantly lower than that of the other groups (P<0.05), while salinity 12 ‰, 24 ‰, and 32 ‰ groups had no significant differences (P>0.05). The concentrations of Na+ and K+ in serum decreased with the decrease of salinity, and the concentrations of Na+ and K+ in salinity 6 ‰ group were significantly lower than that in the control group (P<0.05), while salinity 12 ‰, 24 ‰, and 32 ‰ groups had no significant differences (P>0.05). There was no significant difference in the concentration of Cl- in serum among the groups (P>0.05). Muscle water content increased with the decrease of salinity, but there was no significant difference among the groups (P>0.05). With regression analysis, there was a linear correlation between serum osmolality and ambient water osmolality: Y=0.0781X+317.14 (R2 = 0.82, P<0.05), and the intersection of the regression line and the isosmotic pressure line was the isosmotic point calculated as 343.73 mOsm·kg-1, and the corresponding salinity was 12.59 ‰. The activity of Na+/K+ATPase in gills first decreased and then increased in a “U” shape with the decreasing salinity. The lowest activity of Na+/K+ATPase appeared in salinity 12 ‰ group, which was significantly lower than that of other groups (P<0.05), and there was no significant difference between salinity 6 ‰, salinity 24 ‰ or salinity 32 ‰ (P>0.05). With salinity decreasing, the expression of NKA α1 in gill had no significant difference among the groups (P>0.05). The expression of NKA β1b in gill first decreased and then increased, and the expression in salinity 12 ‰ group was the lowest, which was significantly lower than that of other groups (P< 0.05). The expression of NKA α2a in gill first increased and then decreased with the decreasing salinity, the expression at salinity 12 ‰ was the highest and significantly higher than that at salinity 6 ‰, 24 ‰, 32 ‰ (P< 0.05), and there was no significant difference in salinity 6 ‰, 24 ‰, 32 ‰ (P>0.05); the expression of NKA α3 in gill decreased with the decreasing salinity, the expression at salinity 6 ‰ was the lowest and significantly lower than that at salinity 12 ‰, 24 ‰, 32 ‰ (P< 0.05), and the expression of salinity 32 ‰ was the highest and significantly higher than that at salinity 6 ‰, 12 ‰, 24 ‰ (P<0.05). Gill chloride cells of juvenile Epinephelus fuscoguttatus were mainly distributed in gill filaments and the base of lamellae of all salinity groups. With the decreasing salinity, the number of chloride cells in gill filaments first decreased and then increased; the least appeared at salinity 12 ‰, which was significantly lower than that at salinity 6 ‰ and 32 ‰ (P<0.05). The number of chloride cells in gill lamella was the highest at salinity 32 ‰, significantly higher than that at salinity 6 ‰ and 12 ‰ (P<0.05). There was no significant difference in the diameter of chloride cells in gill filaments and lamella among experiment groups (P>0.05). The oxygen consumption rate increased as salinity decreased, and the lowest rate was at salinity 32 ‰, which was significantly lower than that at salinity 6 ‰ and 24 ‰ (P<0.05), but not significantly different from that at salinity 12 ‰ (P＞0.05). There was no significant difference in oxygen consumption rate among salinity 6 ‰, salinity 12 ‰ or salinity 24 ‰ (P>0.05). The findings indicated that juvenile Epinephelus fuscoguttatus had a strong osmoregulatory ability and could effectively adapt to salinity changes in the range of 32 ‰ within 10 d.  However, in salinity 6 ‰ group, feeding almost stopped and activity decreased, indicating that juvenile Epinephelus fuscoguttatus had been subjected to stress at salinity 6 ‰. The changes of Na+/K+ATPase activity in gills were affected not only by the expression of NKA genes, but also by the number of chloride cells in gill. The energy consumption on osmoregulation may occupy a relatively small part of total metabolism in Epinephelus fuscoguttatus.  It is suitable for its growth in a natural habitat within a salinity of 32‰. In summary, it is helpful to understand the theoretical mechanism of osmotic regulation and salinity control of Epinephelus fuscoguttatus aquaculture. Keywords: Epinephelus fuscoguttatus; salinity; osmoregulation; Na+/K+ATPase Related Articles | Metrics

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Effects of low salinity on the composition of amino acids and fatty acids from juvenile Scylla paramamosain 2022, 44(3): 328.  Abstract ( 158 )   PDF (779KB) ( 364 )   Effects of low salinity on the composition of amino acids and  fatty acids from juvenile Scylla paramamosain WANG Yamei1,2，ZHAO Ming1,2， MA Lingbo1，MA Chunyan1，ZHU Zhifa2， SHI Fangfang1,2，WANG Xueyang1,2，WANG Wei1，JIANG Keji1，ZHANG Fengying1 ( 1．Key Laboratory of Oceanic and Polar Fisheries，Ministry of Agriculture and Rural Affairs，East China Sea Fisheries Research Institute，Chinese Academy of Fishery Sciences，Shanghai 200090，China;  2．College of Fishery and Life Science，Shanghai Ocean University，Shanghai201306，China ) Abstract: Salinity is an important abiotic factor affecting the survival, growth and physiology of crustaceans. The physiological response of aquatic animals to salinity involves content change of amino acids and fatty acids in some tissues such as muscle and hepatopancreas. The contents and compositions of stored amino acids and fatty acids in crustaceans can reflect the individual nutrition level, feeding status, health level and ability of physiological and biochemical regulation challenged by environmental changes. The mud crab Scylla paramamosain belongs to the genus Scylla, family Portunidae, order Decapoda, and is one of the most ubiquitous aquatic animals artificially cultivated crustacean species in China. It often distributes in the marshes with slightly less salinity than sea water, such as estuary, intertidal zone and mangrove forest. It is one of the most popular economic crabs in the southeast coast of China for its rapid growth, large adult size and rich nutrition. With the development of economy and the improvement of life quality, the demand for aquatic products increases rapidly. And aquatic products are favored due to their features of low fat and high protein. Due to the gradual lack of marine resources, aquaculture has become an important way of fishery development. At the same time, the desalination of seawater breeding is also one of the important developed aspects in aquaculture, which can reduce the pollution of mariculture in the coastal marine region, promote the development of inland aquaculture, and reduce the cost of breeding. Scylla paramamosain is a preferred species for lowsalinity aquaculture because it is a euryhaline crab with strong osmoregulatory capacity. In order to explore the effects of low salinity culture environment on amino acids and fatty acids in muscle and hepatopancreas of juvenile Scylla paramamosain, the compositions and contents of amino acids and fatty acids in muscle and hepatopancreas were studied after 30 days of culture at three different salinities. The stage II juvenile crab used for the experiment was taken from the breeding base of the laboratory in Fujian. A total of 630 healthy individuals with the same size, strong vitality and complete artus were selected, with the average body mass of (19.53 ± 0.39) mg. Three salinity gradients were set up as salinity 20, 10 and 0. Each salinity group was set up for a total of 210 juveniles, and each 70 juvenile crabs were placed in a breeding tank as a parallel. The breeding experiment time was 30 days. At the end of the breeding experiment, samples were taken after 24 h of abrosia. In order to exclude the influence of the molting cycle on nutrient composition, Scylla paramamosain in the same molting stage were transferred from the water circulation system to the laboratory, dissected, and the muscle and hepatopancreas were taken respectively. Thirty animals were sampled for each salinity group, and 10 animals were taken for each parallel group, and stored in -80 ℃. The contents of total amino acids (TAA), essential amino acids (EAA), nonessential amino acids (NEAA) and delicious amino acids (DAA) were salinity 20>10>0 group (P<0.05) in muscle. In hepatopancreas, the contents of TAA and NEAA were salinity 10>0>20 group (P<0.05). In the low salinity group, the decrease in muscle and the increase in hepatopancreas of NEAA was more than that of EAA obviously. From the composition of amino acids, NEAA ratio was higher than EAA in the muscle in all salinity groups. Comparing the two tissues, the proportion of EAA was higher in hepatopancreas than that in muscle, and the proportion of NEAA and DAA was higher in muscle than that in hepatopancreas. Challenged by low salinity, the NEAA ratio decreased in muscle but increased in hepatopancreas. The contents of fatty acids in muscle was lower than that in hepatopancreas. The contents of total fatty acids (TFA), saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) was salinity 0>10>20 group (P<0.05) in muscle, and was salinity 20>10>0 group (P<0.05) in hepatopancreas. The highest proportion was SFA in each tissue, followed by PUFA and the lowest was MUFA. Both SFA and PUFA ratios in muscle were higher than that of hepatopancreas, while MUFA ratio was lower than that of hepatopancreas. SFA ratio increased in muscle and decreased in hepatopancreas under low salinity. The proportion of PUFA, n3PUFA and DHA was salinity 10>20>0 group in hepatopancreas, which was the same as the sum of that in muscle and hepatopancreas. According to the sum of amino acids or fatty acids content in muscle and hepatopancreas tissues of each salinity group, TAA content increased by 0.36% and TFA content decreased by 25.61% in salinity 10 group compared with salinity 20 group; TAA content decreased by 8.14% and TFA content decreased by 42.51% in salinity 0 group compared with salinity 20 group. Under the condition of chronic low salinity, the content and composition of amino acids and fatty acids in muscle and hepatopancreas of Scylla paramamosain significantly changed. The amino acids content in muscle decreased, but increased in hepatopancreas. The accumulation of total fatty acids in two tissues of low salinity group (10 and 0) decreased significantly. In two tissues of salinity 10 group, total amino acids contents increased, but total fatty acids content decreased; in two tissues of salinity 0 group, the total amino acids and total fatty acids content decreased. Results showed that amino acids and fatty acids in muscle and hepatopancreas changed significantly under chronic low salinity stress. The content of amino acid in muscle decreased, but increased in hepatopancreas. The content of fatty acids increased a little in muscle, and decreased significantly in hepatopancreas. Based on the sum of the contents of amino acids or fatty acids in two tissues in each salinity group, the total amino acid content, n3PUFA and DHA increased in salinity 10 group, but total fatty acids content decreased. However, challenged by 0 salinity, the total amino acids content, total fatty acids content, n3PUFA and DHA in two tissues decreased. This study provides basic data for the change of nutrient composition of Scylla paramamosain under low salinity culture. Studies on the metabolic mechanism of amino acids and fatty acids should be further explored in order to research their roles in adaptation to environmental salinity changes in the future. According to the change trend of nutrients among three salinity gradients in this experiment, the nutritional physiology and nutritional demand test can be further carried out to improve the survival rate and growth property of Scylla paramamosain under low salinity stress. Keywords: Scylla paramamosain; low salinity; amino acids; fatty acids Related Articles | Metrics

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Analysis on selection effect and growth advantage of a fifth generation selected line of red shell colored Meretrix meretrix 2022, 44(3): 340.  Abstract ( 142 )   PDF (1189KB) ( 362 )   PDF（mobile） (907KB) ( 6 )   Analysis on selection effect and growth advantage of a fifth generation  selected line of red shell colored Meretrix meretrix WU Yangping, CHEN Aihua, ZHANG Yu, ZHANG Zhidong,  CAO Yi, CHEN Suhua, SUN Xuefeng, LI Qiujie (Jiangsu Institute of Marine Fisheries, Jiangsu Provincial Fine Breeds of Meretrix, Nantong Jiangsu226007,China) Abstract: Meretrix meretrix is widely distributed in coastal areas of China, and Jiangsu Province is the main production area of M. meretrix. In recent years, the eutrophication of aquaculture water in shrimp and crab ponds due to high input of feed has reached the red line of environmental protection, and trapping shellfish has become a necessary solution to improve aquaculture water quality, energy conservation and emission reduction. As the most important shellfish in Jiangsu Province, the culture space of M. meretrix can be further extended to shrimp and crab ponds in addition to the traditional tidal flat and pond culture. Therefore, it is necessary to breed a new species of M. meretrix to better match with other species such as shrimp and crab, and jointly promote the ecological transformation of pond in feeding, catching and other daily aquaculture management, so as to achieve green and highquality development. So far, four new varieties of M. meretrix breeding have been announced by the Ministry of Agriculture and Rural Affairs. However, the lack of local varieties of M. meretrix industry in Jiangsu Province does not match with the highly developed M. meretrix industry. It is urgent to breed new varieties of M. meretrix in Jiangsu Province to support the development of the existing industry. Since 2007, a continuous population breeding process has been carried out by selecting M. meretrix with red color shell from YaoshaLengjiasha sand sea area in Rudong. Until 2018, it had been continuously bred for 5 generations. In 2018, 4 000 seeds were randomly selected from the breeding line G4 to measure the shell length and weight under the indoor conditions in Jiangsu Provincial Fine Breeds of Meretrix. The first 40 seeds were selected as the breeding group of the fifth generation (G5) by sorting the shell length and grain weight, and the seed retention rate was 1% and the selection strength was 2.665. In addition, 40 seeds were randomly selected from the same breeding line G4 as the control group without breeding. The parents of the breeding group and the control group were subjected to induction of spawning. During the breeding process, at larval stage, the shell length and shell height of the selected group and the control group were measured by random sampling every afternoon. After attachment, the shell length and shell height of the selected group and the control group were randomly sampled at 7, 13, 32 days old. 67, 102, 143, 252, 310, 328, 358dayold individuals were randomly sampled and measured. At 310 days of age, the selected group and the control group were placed in the same pond for breeding. The shell length, shell height, shell width and grain weight were measured once a month. In this study, the selection response, realized heritability h2R and genetic gain of the fast growing and breeding line G5 established in 2018 were evaluated and compared with the control group without breeding. Results showed that the shell length, shell height, shell width and grain weight of the selected group were significantly higher than those of the control group at larval stage, intermediate cultivation stage and growout stage in most time (P < 0.05). In harvest, the shell length, shell height, shell width and grain weight of the selected group were (43.020±3.267) mm, (35.948±2.757) mm, (19.838±1.768) mm, (22.008±4.755)g, while the shell length, shell height, shell width and grain weight of the control group were (40.019±3.644) mm, (33.446±3.091) mm, (18.449±1.860) mm, (17.755±4.527) g. The average values of selection effect of shell length and shell height at larval stage were 0.40±0.28 and 0.46±0.31, respectively. The average values of genetic gain were 1.09%±0.68% and 1.44%±0.95%, respectively. The average values of realized heritability were 0.15±0.11 and 0.17±0.11, respectively. The average values of selection effect of shell length and shell height at the intermediate cultivation stage were 0.62±0.20 and 0.63±0.09, respectively. The average values of genetic gain were 11.17%±8.30% and 7.28%±3.36%, respectively. The average values of realized heritability were 0.23±0.07 and 0.24±0.03, respectively. The average values of selection effect of shell length, shell height, shell width and grain weight at growout stage were 0.63±0.22, 0.74±0.14, 0.64±0.21, 0.73±0.19, respectively. The average values of genetic gain were 8.64%±2.78%, 8.18%±1.64%, 6.87%±1.41%, 28.18%±8.12%, and the average values of realized heritability was 0.24±0.08, 0.28±0.05, 0.24±0.08, 0.27±0.07, respectively. In quantitative genetics research, h2R<0.15 is usually defined as low heritability，0.15<h2R<0.3 is defined as medium heritability and h2R>0.3 is defined as high heritability. In this study, although the red shell colored breeding line of M. meretrix has been continuously selected for five generations, the heritability of shell length, shell height, shell width and grain weight is still at a medium level of 0.24. From the genetic gain of grain weight of target traits, there is still large selection space from selection limit. In the study, it was also found that the heritability at the development stage was greater than that at the intermediate culture stage of juvenile M. meretrix, and at the intermediate culture stage juvenile M. meretrix was greater than that at the larval stage, which was consistent with the fact that the growth heritability at the development stage varied greatly and the adult growth heritability was generally greater than that at the larval stage. In this study, the genetic gains of shell length, shell height and shell width in the incubation period were similar, all of which were about 7.50 %, while the genetic gains of grain weight reached 23.96%. This was mainly due to the correlation between the four parameters of shell length, shell height, shell width and grain weight of bivalves, and the grain weight showed a power function relationship with shell length. The existing studies on the phenotypic parameters of bivalves confirmed the close relationship between weight traits and shell shape traits. Therefore, a small increase in shell length, shell height and shell width led to a significant increase in grain weight, and the same findings were found in other studies. The research results can clarify the superiority of selfselected new lines of M. meretrix and provide basic information for new varieties identification and extension. Keywords: red shell colored M. meretrix; mass selection; genetic parameters Related Articles | Metrics

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Risk assessment of heavy metals in Meretrix meretrix culture area of Qidong City based on multivariate evaluation method  2022, 44(3): 350.  Abstract ( 126 )   PDF (1189KB) ( 370 )   Risk assessment of heavy metals in Meretrix meretrix culture  area of Qidong City based on multivariate evaluation method  HU Zhenxin1, XIAO Lixia1, TAO Ye1, ZHU Tianjun1, FENG Chunlei2 (1. Fishery Technology Extension  Station of Qidong, Qidong Jiangsu226200, China; 2. East China Sea  Fisheries Research Institute, Chinese Academy of Fishery Sciences, Shanghai200090, China) Abstract: The seas with high population density are submitted to numerous anthropogenic pressures. Chemical pollution by heavy metals coming from continental human activities are transported through rivers or by air and accumulate in seas where they mainly affect coastal areas. Heavy metals exist widely in soil, the atmosphere, and watersediment systems, heavy metals can accumulate and become magnified in living organisms due to their persistence, high enrichment, and ease of migration. As a consequence, even low concentrations of metals pose potential threats to organisms, including humans. Qidong City, Jiangsu Province is located on the coast of the Yellow Sea at the mouth of the Yangtze River. It has a long coastline and rich tidal flat resources. It is a famous clam breeding base in China. In recent years, with the expansion of the breeding scale, the discharge of sewage from various sources along the coast, the occasional largescale death of shellfish cultured on the beach, pollution in the breeding area has become a common occurrence in marine aquaculture. In this study, the content and distribution characteristics of heavy metals Cu, Zn, Pb, and Cd in the water and sediment of Qidong clam culture area during 2017—2019 were systematically analyzed and summarized. In order to study the status of heavy metals and ecological risks of Meretrix meretrix culture areas of Qidong City, the probabilistic ecological risk assessment method was employed to evaluate the ecological risks of the water body，while sediment quality guidelines (SQG) was applied to analyze the biological toxicity of sediment. This study showed that the content of four heavy metals in the sea water of Qidong clam aquaculture was relatively low. The threeyear average concentrations of Cu, Zn, Pb and Cd from high to low were: Cu (3.6 μg··L-1), Zn (0.2 μg··L-1), Pb (0.18 μg··L-1), Cd (0.06 μg··L-1). Since there were no largescale enterprises around the sea area, combined with the low heavy metal content in this sea area, it showed that the water body in the study area was not significantly polluted by heavy metals. The concentrations of Cu, Zn, Pb, and Cd were relatively higher in station 1 and station 2, which were near the shore. The main reason for this distribution was that there were many electroplating, steel wire rope and textile dyeing and finishing enterprises in Haian and Tongzhou in Nantong City, and the near shore was affected by various sources of heavy metal contaminants from industrial production discharge, domestic sewage, agricultural water or ship discharge, etc.  In sea areas far from the shore, after landbased pollutants entered the ocean, with the flow of water and strong water exchange capacity, terrestrial pollutants migrated and diffused. Coupled with the selfpurification of water, the concentration of heavy metals was low. The exposure concentrations of Cu, Zn, Pb, and Cd corresponding to the cumulative probability of 90% were 4.77, 2.33, 1.91, 1.75 μg··L-1, respectively. The acute toxicity data of Cu, Zn, Pb, and Cd corresponding to the cumulative probability of 10% were 4.81, 2.51, 3.13, 3.52 μg··L-1，the ecological risks assessment of four kinds of heavy metals showed that the value of MOS10 was more than 1, indicating that these areas had low ecological risk of heavy metals pollution. The probabilities of four heavy metals affecting more than 10% of aquatic organisms were 50.05%, 25.38%, 24.01% and 19.09%, respectively. In the sea water the ecological risk of four main heavy metals was in order of Cu>Zn>Cd>Pb. In surface sediments, the contamination degree of heavy metals was Zn＞Pb＞Cd＞Cu. The potential biological toxicity was analyzed using sediment quality guidelines (SQG), the guideline values showed that the content of Cd at each station was lower than that of TEL, indicating no Cd potential biological toxicity. The Cu content of 33.33% site and the Pb content of 46.70% site had no potential biotoxic effects, the Cu content of 66.67% site, the Zn content of 50% site and the Pb content of 53.30% site were between TEL and PEL. As for sediment it showed occasional potential biological toxicity in every sampling station, Cu, Pb, Cd showed potential biological toxicity in some sampling stations. Longterm exposure will have toxic effects when the pollutant content in sediment samples is higher than TEL, and acute toxic effects will occur when the pollutant content is higher than PEL. Among them, the potential biological toxicity of Zn was the most frequent. The value of ∑TUs of four heavy metals was above 6 in station 1 and station 2, indicating that there was obvious acute toxicity in these two stations, and the ∑TUs value was mainly contributed by Zn, which was consistent with the high probability of the toxic effect of Zn on organisms. For the other stations the values of ∑TUs were less than 4. Basically, there were no acute toxic effects on aquatic organisms. Following the value of ∑TUs, it indicated that there was heavy metal acute toxicity in only two of the sampling stations (station 1 and station 2), no heavy metal acute toxicity in the other stations. It was recommended that sitespecific risk assessments be conducted to assess possible ecological effects at these sites. Different potential biotoxic effects of the four heavy metals were related to their respective heavy metal contents and their critical effect concentration (TEL). The concentration of Cd was significantly lower than that of TEL, the content of Cu and Zn were significantly higher than that of TEL, and the content of Pb was not much different from that of TEL. The toxicity and bioaccumulation of heavy metals to aquatic organisms can be affected by various environmental factors, such as pH value and salinity of the water environment, which will directly affect the form of heavy metals in water and change the toxicity of heavy metals. It is very important to focus on the functions and roles of various organisms in the ecological environment and to evaluate the risk effect of heavy metals on aquatic organisms in further research. The analysis results provide a scientific basis for the risk management and evaluation of heavy metals in shellfish farming areas. Keywords: Qidong City; Meretrix meretrix; heavy metals; risk assessment Related Articles | Metrics

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Effect of stiffened structure on hydrodynamic performance of V-shaped otter board 2022, 44(3): 360.  Abstract ( 159 )   PDF (8904KB) ( 400 )   Effect of stiffened structure on hydrodynamic performance  of V-shaped otter board ZHANG Huaizhi1,2,3, CHU Wenhua1,2,3, YIN Chunqing1,2,3,5, YUN Qing1,2,3, YE Xuchang1,2,3, YE Qian4 (1. College of Marine Science, Shanghai Ocean University, Shanghai201306,China; 2. National  Research Center of Ocean Fishery Engineering and Technology, Shanghai201306, China;  3. Experimental Teaching Demonstration Center for Marine Science and Technology，Shanghai  Ocean University, Shanghai201306, China; 4. Taizhou University, Taizhou Zhejiang318000, China； 5. Shanghai Engineering Research Center of Marine Renewable Energy, Shanghai201306, China) Abstract: As an important accessory of trawl fishing gears, the hydrodynamic performance of otter board has a very important impact on the operability and catch efficiency of trawl fishing gears. The Vtype otter board is symmetrical in front and back and can be exchanged between left and right, it has the advantages of convenient operation, good stability and easy automatic recovery after falling down. Therefore, Vtype otter board is widely used in offshore trawlers in China. In recent years, to improve the structural strength and stability of Vtype otter board, several largescale stiffeners have been added to the traditional structure in the design and manufacture of Vtype otter board, but there has been no detailed corresponding theoretical research on the influence of these stiffeners on the hydrodynamic performance of Vtype otter board. This study takes the stiffened Vtype otter board configured by Chinese offshore trawlers as the research object, and uses computational fluid dynamics (CFD) software to calculate and analyze its hydrodynamic performance. Through the comparative analysis of the hydrodynamic performance of stiffened Vtype otter board with the traditional unstiffened Vtype otter board, the influence mechanism of the stiffener on the hydrodynamic performance of the Vtype otter board is studied, and the validity of the numerical calculation results is verified by dynamic flume test. On this basis, by changing the aspect ratio, plate folding angle and other design parameters, its influence on the hydrodynamic performance of stiffened Vtype otter board is studied to provide reference for the structural optimization design of new Vtype otter board. Through comparison, the numerical model of stiffened Vtype otter board established in this study is highly effective, with the relative error of lift coefficient of 13.5%27.5%, the average relative error of 24.8%, the relative error of drag coefficient of 4.7%20.5%, and the average relative error of 16.8%. The shape and value of lift drag ratio curves agree well with each other, and the average relative error is 9.0%. The influence of design parameters such as aspect ratio, plate folding angle and stiffener size on the hydrodynamic performance of stiffened Vtype otter board is studied. Results show that the addition of several largescale stiffeners to the Vtype otter board not only increases the structural strength and stability, but also changes the distribution of the surrounding flow field when the otter board works in water. Compared with the traditional unstiffened Vtype otter board, the flow on the back flow surface of stiffened Vtype otter board is more complex and chaotic, and the number of vortices increases. At a small angle of attack (below 40 °), the pressure distribution on the upstream and downstream surfaces of the otter board is not significantly affected by the stiffened structure, which shows that there is little difference between the rise coefficient and resistance coefficient of stiffened Vtype otter board and unstiffened Vtype otter board. However, at large angles of attack (above 40 °), the pressure difference between the upstream surface and the downstream surface of stiffened Vtype otter board decreases significantly, and the rise coefficient and resistance coefficient of the otter board decreases significantly. Since the working angle of attack of Vtype otter board usually does not exceed 40 ° in actual operation, from the perspective of expansion effect, the addition of stiffened structure on the back of Vtype otter board will not have a significant impact on its working performance. The existence of stiffeners reduces the lift drag ratio of Vtype otter board by 1.20 under the optimal working angle of attack (about 10 °). After adding stiffeners, the maximum lift drag ratio of Vtype otter board will still increase gradually with the increase of aspect ratio, but the maximum lift drag ratio of Vtype otter board decreases obviously under each aspect ratio. The changing trend of lift coefficient, drag coefficient and lift drag ratio curve will not be changed by the change of plate folding angle of stiffened Vtype otter board, but the maximum lift drag ratio will increase significantly with the increase of plate folding angle. Moreover, with the increase of the plate angle, the height of the stiffener will gradually decrease due to the change of the structure, and its influence on the flow field distribution on the back flow surface of the otter board will gradually decrease. When the space of stiffeners is small (less than 430 mm), it has little impact on the hydrodynamic performance of the otter board. When the space of stiffeners is large, the maximum lift drag ratio of Vtype otter board will be significantly reduced, and the increase of its size will also reduce the lift drag ratio of otter board to a certain extent. The increase of stiffener size will also reduce the lift drag ratio of otter board to a certain extent, but the reduction range is not obvious. Therefore, when designing the reinforced Vtype otter board structure, the stiffeners should be arranged as close to the middle of the mesh plate as possible, and the space of stiffeners should not be too large. At the same time, it can be considered to appropriately increase the width of the stiffeners, so as to further improve the structural strength and stability of the otter board on the premise of ensuring high hydrodynamic performance. To sum up, reducing the space and size of stiffeners, increasing the aspect ratio and reducing the plate folding angle can improve the hydrodynamic performance of stiffened Vtype otter board. Considering the actual working environment, the Vtype otter board is the bottom trawl otter board located on the seabed when working, it is not convenient to adjust its posture at any time, so it needs to have good stability and sufficient structural strength. The stability of stiffened Vtype otter board is negatively related to its aspect ratio and plate surface folding angle, and the structural strength is also closely related to the space and size of stiffeners. Therefore, when designing the structure of stiffened Vtype otter board, it is necessary to improve and optimize it on the basis of comprehensively considering these factors.  Keywords: hydrodynamic performance; impact parameters; numerical simulation; stiffened Vtype otter board Related Articles | Metrics

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A review: Molecular breeding related techniques of Larimichthys crocea 2022, 44(3): 375.  Abstract ( 235 )   PDF (672KB) ( 424 )   A review: Molecular breeding related techniques  of Larimichthys crocea PENG Shiming1, WANG Yabing1, WANG Qian1, GAO Quanxin2,  ZHENG Hanfeng1, XU Jian3, WANG Lumin1 (1. East China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Shanghai200090,  China; 2. College of Life Science, Huzhou University, Huzhou Zhejiang313000, China;  3. Chinese Academy of Fishery Sciences, Beijing100141, China) Abstract: Large yellow croaker (Larimichthys crocea) is an important mariculture fish in China, and its annual output ranks first in cage culture in China. In order to further promote highquality development of Larimichthys crocea culture industry, many scholars in China have successively carried out research on the selection and breeding of Larimichthys crocea , and have made good progress. The excellent varieties of Larimichthys crocea “Minyou No. 1”, “Donghai No. 1” and “Yongdai No. 1” came out successively, which promoted the construction of the integrated industrial system of “breedingreproductionpromotion” of Larimichthys crocea in China. Although varieties with excellent economic traits can be discovered through population and family selection, traditional breeding techniques have shortcomings such as long cycle, low efficiency and poor predictability, which greatly limit the development of Larimichthys crocea breeding industry.  As early as the 1960s, some scientists put forward the idea of breeding based on molecular markers, but this advanced point of view did not receive extensive attention from the academic circles. In the 1990s, the DNA molecular markers had been gradually valued and excavated, and after decades of rapid development, molecularassisted breeding technology has gradually become the focus of guiding global fish breeding innovation. Early application of DNA molecular markers mainly included restriction fragment length polymorphism (RFLP), amplified fragment length polymorphism (AFLP), simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers, etc. SSR and SNP markers have gradually become the main technologies in the field of global molecular markerassisted breeding due to their high polymorphism, easy detection, and high genetic stability. After entering the 21st century, SSR and SNP markers began to be used for genetic improvement research of Larimichthys crocea . With the rapid development of molecular biology and sequencing technology, as well as the deciphering of Larimichthys crocea genome, new genotyping and analysis techniques have emerged, and have been widely used in Larimichthys crocea breeding research. RADseq technique, started in 2007, used restriction enzyme in genome cutting and high throughput sequencing. RADseq does not need the whole genome, thus it can be applied in all aquatic animals, and it has the advantage of low cost. WGR can be used for whole genome sequencing of different species, fully interpreting the genetic variation information and evaluating the correlation between the variant information and economic traits. Using whole genome resequencing (WGR) and restrictionsiteassociated DNA sequencing (RADSeq) technology can mine a large amount of SNP information, which lays the foundation for SNP typing. Then, based on the genotype data, a highdensity genetic linkage map can be constructed and used for quantitative trait locus (QTL) mapping and genomewide association study (GWAS). A series of SNP loci related to economic traits of Larimichthys crocea  have been identified, including growth characteristics, disease resistance, gonadal development and stress resistance traits. Based on these SNPs, markerassisted selection (MAS) and genomewide selection (GS) have been used for Larimichthys crocea breeding. Now, with the rapid development of highthroughput sequencing technology, rapid reduction of sequencing cost, and more accurate genome assembly technology, a large number of candidate genes and genetic loci have been discovered and reported in Larimichthys crocea , providing a solid foundation for molecular breeding of Larimichthys crocea . Some molecular breeding techniques have been used in the breeding of Larimichthys crocea and achieved remarkable results. The development of modern gene sequencing technology has promoted the innovation of breeding technology. The breeding technology of Larimichthys crocea is bound to make continuous progress with the development of genetic theory and technology. Larimichthys crocea molecular breeding in China starts late, so the foundation is weak. However, our country has unique industrial conditions such as abundant germplasm resources and huge market demand, which has promoted the development of molecular breeding of Larimichthys crocea . At present, the research and application of biological breeding technology presents a trend of contention in China, with broad prospects for development. The continuous maturation and breakthrough of molecular breeding technology will lead to the great reform of traditional breeding methods. This paper summarizes the research progress of major molecular selection techniques in breeding field of Larimichthys crocea , including RADSeq, genetic linkage map and QTL mapping, GWAS, WGR, SNP array, GS and gene editing technology. The development and application of breeding technology of Larimichthys crocea are prospected. Germplasm is the foundation for the sustainable development of auqaculture, also the key part in the aquaculture field in the 14th Five Year Plan period and the future. Currently, the innovation and research of Larimichthys crocea  germlpasm is facing a advantageous situation. Though china has made important progresses in genetic breeding field of Larimichthys crocea, it still has limitations in cuttingedge breeding techniques, efforts should be made in hot spot fields and techniques.First, the gene editing breeding of Larimichthys crocea is still in its infancy. A large number of major genes related to economic traits have now been discovered. In the future, gene editing technology will be used to accurately analyze the function of target genes, and to carry out germplasm creation to achieve the purpose of optimizing traits. Second, GS technology is an efficient breeding method based on genomewide molecular markers for breeding value calculation and selection. It can be combined with today’s hot omics technology and artificial intelligence to design breeding programs and build a theoretical system for precise control of complex traits, thereby bringing new vitality to the scientific and technological innovation of omics breeding industry. Third, as an emerging research field, intestinal microbiota is crucial for the healthy development of Larimichthys crocea , and is significantly related to host genes and economic traits. In the future, the integration of the model “economic traitsintestinal microbiotagenetic genes” can be constructed, to provide a new theoretical perspective and technical support for the innovation of Larimichthys crocea breeding. Keywords: Larimichthys crocea ; genetic improvement; molecular breeding; research progress; prospect  Related Articles | Metrics