Effects of salinity stress on survival, antioxidant enzymes and 

Na+/ K+ATPase activities of Moerella iridescens

PEI Ruihua1,2, ZHENG Ziyao1,2, ZHANG Nuo1,2, LIU Qigen1,2, CHEN Liping1,2, HU Zhongjun1,2

（1. Key Laboratory of Freshwater Aquatic Genetic Resources of Ministry of Agriculture and 

Rural Affairs, Shanghai Ocean University, Shanghai201306, China； 2. Centre for Research on 

Environmental Ecology and Fish Nutrition (CREEFN) of the Ministry of Agriculture and 

Rural Affairs, Shanghai Ocean University，Shanghai201306, China）

Abstract: Salinity is an important ecological factor relative to the survival, reproduction, growth, and development of aquatic life forms through influencing the energy consumption in the process of osmotic regulation and antioxidant enzyme activity of animal’s organism. The salinity of estuary changes drastically, which will exert a great physiological stress on shellfish with limited migration ability. The sodiumpotassium ATP enzyme (Na+/ K+ATPase) is an important dynamic component of sodiumpotassium pump, and its activity is often used as an important indicator of osmotic regulation ability in animals. Free radical scavenger enzymes such as superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSHPx) are important members of the antioxidant enzyme system and are effective indicators to assess the effect of the environment on life form. Rainbow clam (Moerella iridescens) is an intertidal shellfish with high economical value. Historically, it was a dominant species in intertidal zone of the Yangtze River Estuary. Moerella iridescens is required to be protected urgently for its sharp decline in population size and drastic contraction in distribution area under multiple environmental stresses. However, the salinity in estuary fluctuates largely. Shellfishes inhabiting in estuaries often regulate body functions to adapt to environmental changes. Therefore, it has important scientific significance and application value for protection and rearing of Moerella iridescens to reveal its adaptation to salinity variation and its regulation mechanism. In present study, acute stress experiments were carried out to explore the adaptability to salinity and regulation mechanism of Moerella iridescens, in which the mortality rate and activities of Na+/ K+ATPase and three antioxidant enzymes were measured under different salinity gradients and exposure durations. Moerella iridescens was purchased in the aquatic product market of Luchao Port, Pudong New Area, Shanghai. Healthy and vigorous experimental clams, with (17.37±0.36) mm of average shell length, (11.49±0.26) mm of shell height, (5.23±0.12) mm of shell width, and (0.52±0.02) g of wet mass, were selected and kept in a blue plastic box in Shanghai Ocean University with continuous aeration. During temporary culturing, the water, made of sea crystal and aerated tap water, was changed every day and Moerella iridescens was fed Chaetoceros sp. at 1.0×105 cell·mL-1. In the acute salinity stress experiment, the mortality process within 96 h was observed at 24 h interval when they were exposed to water with 10 salinity gradients ranging from 5 to 50 set by the equal logarithmic spacing method, including salinity 50, 39, 30, 23, 18, 14, 11, 8, 6, 5. The activities of SOD, CAT, GSHPx and Na+/ K+ATPase in gill and digestive glands were measured at 0, 24 , 48 , 72, 96 h when they were exposed to water with sanilities of 6, 12, 18, 24, 30. The total protein was determined by Coomasiland method, and the SOD, CAT, GSHPx and Na+/ K+ATPase were determined. The oneway analysis of variance (ANOVA) was used to test the effect of salinity and exposure time on the activities of various enzymes, Duncan’s multiple comparison was used to determine significant differences between the treatment groups, and P<0.05 was used as the significant level of difference. The results showed that the shell color of Moerella iridescens changed to pink in water with salinity of 8 to 18, and they were sensitive to the external stimuli of water pipes and axe feet. However, in the low salinity water with salinity of 5 and high salinity water with salinity of 50, the shell of Moerella iridescens became white, and the water pipes and axe feet responded slowly to external stimuli. The mortality rates followed a Ushaped curve at 96 h of exposure, no death was observed in the experimental groups of salinity 8, 11, 14 and 18; with increasing salinity, the mortality rates declined at salinities below 8(8.3% and 1.7% of mortality rate for salinity 5 and 6, respectively) and increased at salinities above 18(3.3%, 6.7%, 43.3%, and 100% of mortality rate for salinity 23, 30, 39, 50, respectively). Salinity and exposure duration both had significant effects on the activities of SOD, CAT, GSHPx and Na+/ K+ATPase in gills and digestive glands of Moerella iridescens(P<0.05). With the extension of exposure time under the same salinity stress, SOD, CAT, GSHPx and Na+/ K+ATPase in gills and digestive glands of Moerella iridescens increased first, then decreased, and finally tended to be relatively stable. At the same salinity stress, the activities of SOD, CAT and GSHPx reached the peak at 24 h or 48 h, and that of Na+/ K+ATP reached its peak at 48 h or 72 h. This study suggests that the survival salinity of Moerella iridescens ranges from 6 to 30, and its optimal salinity ranges from 8 to 18. The induction of activity of the above four enzymes of gills and digestive glands of Moerella iridescens under salinity stress is characterized by tissue and organ specificity and temporal sequence, and three antioxidant enzymes respond more quickly to salinity stress than Na+/ K+ATPase. The antioxidant defence mechanism will be damaged and osmotic regulation ability might decrease for Moerella iridescens in extremely high or low salinity environment, which finally leads to die. The salinity ranging from 8 to 18 is suggested in farming practices and conservation actions of Moerella iridescens to decrease the stress of unsuitable salinities on it. This study provides a scientific basis for exploring the adaptability and regulation mechanism to salinity and for its farming and conservation.

Keywords: Moerella iridescens; salinity; mortality; antioxidant enzymes; Na+/ K+ATPase activity