Anesthetic effects of eugenol and MS-222 on Trachidermus fasciatus

HU Wangjiao1,2， WANG Cuihua1,2， FENG Guangpeng1,2， ZHUANG Ping2， ZHENG Yueping3，JI Qiang4

(1. College of Fisheries and Life Science, Shanghai Ocean University, Shanghai 201306, China; 2. Shanghai Yangtze 

Estuary Fishery Resources Proliferation and Ecological Restoration Engineering Technology Research Center, East China 

Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Shanghai200090, China; 3. Shanghai Aquatic 

Wildlife Conservation and Research Center, Shanghai202162, China; 4. Shanghai Songjiang District Aquatic 

Technology Promotion Station, Shanghai201669, China)

Abstract: The main purpose of this study is to explore the anesthetic effect of eugenol and MS222 on Trachidermus fasciatus. T. fasciatus is a kind of small benthic, carnivorous, wide temperature and wide salinity migratory fish, whose resources have collapsed in recent years since the 1980s. It was listed as an endangered species in China Red Data Book of Endangered Animals in 1998. Enhancement and release are considered to be important and effective measures for ecological restoration and resource conservation. As the secondary protected aquatic wildlife in China, a lot of T. fasciatus enhancement and releasing has been carried out by relevant departments in recent years. However, some activities such as marking and transportation may cause stress response and damage to the fish, which in turn may reduce the survival rate of T. fasciatus in the process of enhancement and releasing. Anaesthesia is one of the most important means to reduce fish stress and improve survival rates in the releasing. The two most commonly used fish anaesthetics in China are eugenol and MS222, which are generally considered to be safe and effective anaesthetics in aquatic animals, and they have been widely used throughout the world. At present, eugenol and MS222 have been used for anesthesia in numerous fish species at home and abroad, but no relevant studies on their anesthetic effects on T. fasciatus have been reported. This study was conducted to compare the anaesthetic effects of different mass concentrations of eugenol and MS222 on T. fasciatus to provide scientific reference for aquaculture production and releasing of T. fasciatus.

Three different anesthesia experiments were designed by immersion for this experiment. The specific experimental approaches were as follows: 1) Record the final anesthesia degree and recovery status of the fish under different concentrations of eugenol and MS222 anesthesia; 2) Observe and record the time when T. fasciatus entered each anesthesia stage and the time of the recovery stage during the recovery process under two different anaesthetics, with different concentration gradients; 3) The highdefinition shooting was used to measure the respiratory rate of T. fasciatus at different concentrations of two anaesthetics for 30 s, 1 min, 2 min, 3 min, 4 min, 5 min, 6 min and 7 min. 4) The oxygen consumption rate of T. fasciatus was determined by closed hydrostatic respirometry at 5 mg·L-1 and 10 mg·L-1eugenol concentrations and 40 mg·L-1and 50 mg·L-1 MS222 concentrations.

The hydrostatic test was used to analyze the anesthetic effect of two commonly used fishery anesthetics, eugenol (5, 10, 20, 40, 80, 120 mg·L-1) and MS222 (40, 50, 60, 75, 100, 200 mg·L-1), on T. fasciatus with body weight of (13.78 ± 3.15) g. The results were as follows: 1) With the increase of the concentrations of two anesthetics, the anesthesia time of T. fasciatus was gradually shortened and the recovery time was prolonged; 2) Under the experimental conditions, the optimum anesthetic concentration of eugenol and MS222 were 4080 mg·L-1 and 60 mg·L-1, respectively; 3) At low concentration of anesthetics, the oxygen consumption rate of T. fasciatus in 10 mg·L-1 eugenol was significantly lower than that of the control group (P<0.05), suggesting that 10 mg·L-1 eugenol might be a suitable transport concentration for T. fasciatus; 4) Compared with the survival rate, the time of entering anesthesia and resuscitation, eugenol was more suitable for T. fasciatus, and 4080 mg·L-1 eugenol was recommended to use for the anesthetic of T. fasciatus.

In this study, both anesthetics could make T. fasciatus enter different levels of anesthesia. By comparing the anaesthesia time, recovery time and mortality of T. fasciatus, it was found that the effective concentration of eugenol ranged from 20  mg·L-1 to 80 mg·L-1 and the optimum concentration of MS222 was 60 mg·L-1 at water temperature of (15 ± 3) ℃, which was different from many fishes reported in the literature. It showed that the anesthetic effect was not only related to factors such as the type and concentration of anesthetic and the size of the test fish, but there were also significant differences in the sensitivity of different fish species to the anesthetic. In this study, eugenol showed a wider range of safe concentrations and greater tolerance to anaesthesia than MS222.

In addition, it was found that the respiratory rate of the fish decreased gradually as the anaesthetic level increased until the respiration stopped. The difference in the effect of two anaesthetics on the respiratory rate of T. fasciatus might be due to different sensitivities of the fish to different anaesthetics, and the exact mechanism of action needed to be further investigated. In the present study, the oxygen consumption rate of T. fasciatus decreased as the concentration of two anesthetics increased, and the oxygen consumption decreased. In 510 mg·L-1 eugenol treatment, T. fasciatus could enter and remain in sedation or light anaesthesia with slower gill opening and closing, lower respiratory rate and lower oxygen consumption rate. The difference in oxygen consumption rate was significant compared to the control group (P<0.05), which might have some significance in guiding the transport process of T. fasciatus especially at 10 mg·L-1 eugenol. However, the oxygen consumption rate of the fish at 4050 mg·L-1 MS222 concentrations did not differ significantly from the control group. Therefore, 10 mg·L-1 eugenol was recommended for prolonged handling or transport of T. fasciatus, but this still needed to be justified by further transport practice.

Eugenol is cheap and readily available, and has advantages such as fast anesthesia, high recovery rate and wide safety boundaries, which can be used as a suitable anesthetic for T. fasciatus. In this study, the effective anesthetic concentration of eugenol for T. fasciatus is 2080 mg·L-1, and it is recommended to use 4080 mg·L-1 for shortterm operation in production, and should not exceed 80 mg·L-1. 60 mg·L-1 MS222 can make T. fasciatus enter anaesthesia, but the time to enter anaesthesia is longer; 75100 mg·L-1 MS222 can enter anesthesia in a shorter period of time, but the mortality rate is higher and the safety boundary is narrow. Therefore, 4080 mg·L-1 eugenol is recommended for the anesthesia of T. fasciatus in practice, and MS222 may not be suitable as an anesthetic agent for T. fasciatus compared to eugenol.

Keywords: anesthetic; eugenol; MS222; Trachidermus fasciatus; oxygen consumption rate