The Research On Osmoregulation Mechanism Of Silver Pomfret, Pampus Argenteus

Salinity is an ecological factor of considerable importance for bony fish in marineenvironment, including the fish survival, development and growth of larval, juvenileand adult fish. Salinity has powerful effect on life of the migratory fish, silver pomfret(Pampus argenteus). In order to explore its mechanisms, this thesis invested serumosmolality, osmoregulatory hormone and ion-regulatory enzyme of silver pomfret. Inorder to supplement the research of its mechanisms, this thesis also invested effects oflow salinity and different CuSO4concentrations on gill ion-regulatory enzyme activitiesand liver antioxidant function in silver pomfret.The juvenile silver pomfret were cultured in salinity14,25,36for96h at first.Through this experiment, their serum osmolality, ion-regulatory enzyme activities,osmoregulatory hormone concentration and catalase (CAT) activity were tested indifferent salinity over time. The ion-regulatory enzyme include Na+/K+-ATPase (NKA),V-H+-ATPase(VHA), Ca2+-ATPase and carbonic anhydrase(CA). The osmoregulatoryhormone include growth hormone, Insulin-like growth factor-Ⅰ(IGF-Ⅰ) and prolactin(PRL).In this study, the serum osmolality which fluctuated was positively correlated tosalinity, and its variation range is271~379mOsm/kg. The serum osmolality of differentsalinity would return to normal at96h. Serum and gill CAT activities of salinity36and14returned to normal after rose significantly (P <0.05); the highest point of serum wassalinity36at8h, and the point of gill was salinity12at24h. The gill NKA activitiesincreased firstly then recovered as a whole; salinity14at48h, the highest point, wassignificantly different from other points (P <0.05). VHA activities rose then recoveredin salinity14, kept stable in control salinity, fall down then recovered in salinity36.Ca2+-ATPase activities increased significantly when salinity changed (P <0.05), and thevariation trend in salinity14was more identifiable than it in salinity36. CA activities insalinity14and36both increased significantly (P <0.05), and the highest point was found in salinity36at24h. The serum GH concentrations of salinity36which keepinghigh levels were significantly different from other salinity (P <0.05), and point at8hwas the highest value. The serum IGF-Ⅰ concentrations of salinity14and36bothincreased firstly then recovered. The serum PRL concentrations of salinity14werealways higher than other salinity groups, and its points at8h,24h and48h weresignificantly higher (P <0.05). Through analysis of the data, the serum osmolality wassignificantly negatively correlated to gill VHA activity (P <0.01), and it weresignificantly negatively correlated to CA activity (P <0.01) in low salinity adaption (14and25). But the correlation between the serum osmolality and NKA or Ca2+-ATPaseactivity couldn’t be found. It only illustrated a contrary trend between serum osmolalityand Ca2+-ATPase activity in salinity14. This experiment also found that plasma GHconcentration and gill NKA activity were significantly positively correlated (P <0.01)in low salinity adaption (14and25); plasma PRL concentration and gill NKA activitywere significantly negatively correlated (P <0.01) in high salinity adaption (36and25).In addition, plasma PRL and IGF-Ⅰ concentrations were significantly positivelycorrelated (P <0.01).This research proved that serum osmolality which change with salinity, activateCAT when silver pomfret adapt for different salinity. Then gill NKA, VHA,Ca2+-ATPase and CA involved in ion-regulation to keep the balance of osmotic pressurein silver pomfret. And GH, PRL and IGF-Ⅰwould regulate the process ofosmoregulation. There are some concentrations among serum osmolality, ion-regulationenzyme activity and osmoregulatory hormone concentration.Secondly, the salinity will fall depending on the climate in the experimentalaquaculture areas of silver pomfret. And these ares were polluted to a certain extent bysome heavy metal such as copper. Therefore, it is necessary to investigate the effect ofdifferent CuSO4concentrations on silver pomfret in low salinity sea. This studyinvestigated the effects of low salinity on juvenile silver pomfret firstly. We decreasedsalinity from24to12by three steps，the salinity change of every step was4. When fishwas in a stable condition, they were exposed to copper. The water CuSO45H2Oconcentrations was set to0,0.1,0.3,0.5mg L-1in salinity12, or0,0.5mg L-1insalinity24. The copper expose was sustained for144h. Then two kinds of ion-regulatoryenzyme activities in gill: NKA and VHA activities,there kinds of antioxidants in liver:glutathione (GSH) contents, superoxide dismutase (SOD) and CAT activities of silver pomfret were tested in order to reveal the the effect of water copper on those index ofsilver pomfret in low salinity sea. In this study, NKA and VHA activities rose thendecreased during the salinity decline. After CuSO4added into water，NKA activitiesdecreased with the increase of CuSO4concentration. VHA activities decreasedsignificantly after CuSO4added, especially，the0.3and0.5mg L-1groups at72h. NKAand VHA activities of0.5mg/L groups in salinity24increased at24h then decreased.GSH contents and SOD activities increased significantly through the salinity decline.Meanwhile, CAT activities fluctuated. After CuSO4added into water，GSH contents of0.3and0.5mg L-1groups decreased firstly, then increased significantly at72h. SODactivities of each CuSO4group increased firstly then returned. CAT activities of0.3and0.5mg L-1increased significantly at72h.This study suggested that water copper affected silver pomfret with inhibition ofNKA and VHA, especially, in low salinity. The change of GSH, SOD and CAT canreflect the damage of low salinity and CuSO4on silver pomfret. The resistibility ofsilver pomfret to water copper is between a certain range，but we should pay attention tothe concentrations of heavy metal such as copper in water when the water environmenthas changed, for example, salinity had fallen. Indexes in this thesis can be reference ofsilver pomfret cultivation.