Effects Of Abrupt Salinity On Physiological Factors Of Epinephelus Moara

Epinephelus moara was mainly distributed in the tropical and subtropical area. Due to its good environmental adaptability, delicious taste, big body and economic value, Epinephelus moara had became one of the most important aquaculture species in recent years. Salinity is a considerable important ecological factor for fish fish survival, development and growth. Epinephelus moara was a kind of typical euryhaline fish, and salinity has powerful effect on life of the it. The salinity of cultural water is often in a state of fluctuation for the effect of coastal climate and surface runoff. To adapt to the varied environment and defend body against damage, Epinephelus moara must have an effective antioxidant, immune, metabolic osmoregulation defense mechanism. The impact of abrupt salinity decrease on liver metabolic enzymes, liver antioxidant enzymes and plasma lysozyme, liver metabolic enzymes, gill ion-regulatory enzyme and serum osmolality of Epinehelus moara was studied for the first time in this paper. The results of this study not only enriched the study on the physiology and ecology of fish, but also provided the basis for improving the aquaculture technology under different salinity conditions in the further, which had important theoretical and practical meaning. To test the interactive effects of ambient salinity decrement on Epinephelus Moara, four salinity groups（27, 21, 15, 9） were designed, and the fish livers in each group were sampled at day 0, 1, 2, 3, and 7 to measure the activities of liver antioxidant enzymes: superoxide dismutase（SOD）, catalase（CAT）, glutathione peroxidase（GSH-Px）, total antioxidant capacity（T-AOC）, malondialdehyde（MDA） content; serum immune index: plasma lysozyme; metabolic enzymes: acid phosphatase（ACP）, alkaline phosphatase（AKP）, glutamic-pyruvic transaminase（GPT）, glutamic-oxalacetic transaminase（GOT） and lactate dehydrogenase（LDH）; gill ion-regulatory enzyme: Na⁺/K⁺-ATPase（NKA）,Ca²⁺-ATPase,succinate dehydrogenase（SDH）, lactate dehydrogenase（LDH） and serum osmolality1、Effects of salinity on activities of liver antioxidant enzymes and plasma lysozyme of Epinehelus moara.The results showed that the liver SOD as well as CAT activities first dropped in 1, 2 d（P<0.05） and peaked in 3 d of group 21, then dropped to normal in 7 d. The T-AOC activity was consistent with the SOD and CAT activities, while the MDA content was contrary. On a whole, plasma lysozyme activity dropped（P<0.05） with the decrease of salinity and group 21 peaked in 1 d. To sum up, the results indicate that ambient salinity decrement could effectively stimulate and inhibit the SOD and CAT activity in liver of the Epinephelus Moara in initial stage, thenrecovered. T-AOC activity and MDA content will also corresponding change. Plasma lysozyme activity first increased and then dropped with the elapse of treatment time, thus it plays an important role in immune system.2、Effects of salinity on activities of liver metabolic enzymes of Epinehelus moara.The results showed that the activity of ACP in all groups all increased, and ACP activity in 15 salinity group increased significantly compared to the control at day 2（P<0.05） and then decreased to the normal level at day 7; AKP activity decreased at day 1 and 2, and then increased significantly at day 3; GOP and ACP activities changed in the same way（they all decreased first and then increased）; GOT and ACP activities varied in a same manner（they all increased from beginning to the end）. The results indicated that abrupt salinity decrease from 27 to 21 or 15 could cause stress response of Epinehelus moara; the phosphatase, aminopherase and LDH activities were all inhibited first and recovered afterward; the abrupt salinity decrease from 27 to 9 caused the death of all fish at day 33、Effects of salinity on activities of gill ion-regulatory enzyme and serum osmolality of Epinehelus moara.The results showed that the gill NKA as well as Ca²⁺-ATPase activities first incresesd at day 1 and 2 of group 21 and group 15（P<0.05）, then dropped to normal level at day 7. Serum osmolality decreased first and then increased（P < 0.05）. The SDH activity was consistent with the NKA and Ca²⁺-ATPase activities, while the LDH activity was contrary（P < 0.05）. The results indicated that effects of the abrupt salinity decrease on activities of gill ATPase and serum osmolality of Epinehelus moara was significant. The acclimatization could consist of two phases. Phase I:short time after salinity change,the serum osmolality declined rapidly, triggering the change in organism osmoregulation that the activities of NKA and Ca²⁺-ATPase increased. Phase II:the serum osmolality reverted to tile level before salinity change, ATPase dipped to the lowest level then resumed slowly to the their previous leve1. SOD and LDH activity will also corresponding change, providing energy for osmoregulation.