| Tongue sole (Cynoglossus semilaevis) was a kind of typical euryhaline fishwhich was mainly distributed in the Yellow Sea and the Bohai Sea of China. Due toits delicious taste and economic value, tongue sole had became one of the mostimportant aquaculture species in recent years. There had been some studies about itsadaptation to salinity, but the results obtained were different. Generally it wasbelieved that the optimum salinity range of tongue sole was20-32, however, lowsalinity culture had been conducted in Guangdong province. To identify tongue sole’true ability of adaptation to different salinities, systematic study bad been conductedon the effects of salinity on growth, food intake, feed conversion efficiency, energybudget, energy metabolism enzyme, nonspecific immunity, body composition andosmoregulation of juvenile tongue sole with a increasing range of salinity and aextending the time. The aim of our study was to carry out the real ability of adaptationto different salinities of tongue sole. The results of this study not only enriched thestudy on the physiology and ecology of fish, but also provided the basis for improvingthe aquaculture technology under different salinity conditions in the further, whichhad important theoretical and practical meaning. The main results obtained were asfollows:1Effect of different salinity on growth, energy budget and osmoregulation ofjuvenile tongue soleEffect of different salinity (0,5,10,15,20,25,30）on body composition, energybudget and osmoregulation of juvenile tongue sole were investigated in this study. The results showed that with the increasing of salinity, the specific growth rateincreased at first and then decreased. Specific growth rate obtained a higher level atsalinity15-20, there was no significant difference with salinity10; specific growthrate in freshwater conditions was significantly lower than the other salinitytreatments(P<0.05); the specific growth rate under the salinity5had no significantdifference compared with salinity25-30. The feed conversion rate levels weresignificantly lower than other treatments under freshwater conditions (P<0.05).Apparent digest rate decreased with increased salinity within salinity5-30, andapparent digest rate was at a higher level within the salinity5-20, which wassignificantly higher at salinity5than salinity30(P<0.05), but there was no significantdifference compared with freshwater condition (P>0.05). The proportion of the totalenergy budget energy allocated into growth was only9.42±0.28%in freshwater,which was significantly lower than the other treatments (P<0.05), at salinity15-20,the proportion was significantly higher than the other treatments(P<0.05); and therewas no significant difference among the other treatments(P>0.05). The highestproportion of energy lost in feces was found in the fresh water condition which wassignificantly higher than the other treatments(P<0.05), the proportion at salinity35was significantly higher than the salinity5and10treatments (P<0.05). Energy lost inexcretion in freshwater conditions and salinity25were significantly higher than theother treatment(P<0.05),and the proportion in freshwater was significantly higherthan salinity25treatments (P<0.05). In salinity15conditions, the highest proportionof energy budget was allocated into growth,which can be expressed by the followingequation100C=26.37G+5.37F+8.39U+59.86R. Na~+/K~+-ATPase activity in the gilland kidney first increased and then decreased; the level in the gills in the salinity of10and15was significantly lower than the fresh water condition(P<0.05); whileNa~+/K~+-ATPase activity in kidney at salinity10was significantly lower than the othertreatments (P<0.05), the Na~+/K~+-ATPase activity in kidney under the freshwatercondition increased substantially, which was significantly higher than the othersalinity treatments(P <0.05). 2Effects of acclimation to various environmental salinities on non-specificimmunity enzymes of juvenile tongue soleEffects of various salinities (0,5,10,20and30ppt) on the growth and activitiesof non-specific immune enzymes, including superoxide dismutase (SOD), catalase(CAT), alkaline phosphate (AKP) and acidic phosphate (ACP) in different tissues(liver, gills, muscle and kidney) of juvenile tongue sole（Cynoglossus semilaevis）wereinvestigated in this study. The results showed that the growth of juvenile tongue solewas inhibited significantly at0ppt (P<0.05). The final weights of juvenile fish werehigher at intermediate salinity (10and20ppt). In fresh water treatment, SOD activityin muscle was significantly higher than other treatments, and the highest activities ofSOD in liver was recorded at salinity of20ppt, which was significantly higher thanthe fresh water condition (P<0.05). CAT activities in liver decreased with the increaseof salinity, and those in fresh water was significantly higher than other treatments(P<0.05). AKP activities in renal and muscular increased with the increase of salinity,while those in muscle was found to significantly increased in higher salinities ascompared to the freshwater conditions (P<0.05). The activities of ACP in liver for fishat0and5ppt were found significantly higher than those at20and30ppt). The lowestlevels of ACP activities were found in gills and kidney at5ppt. Results from thepresent study indicated that the juvenile tongue sole in the present size was found tobe not suitable for fresh water culture. However, salinities above5ppt have noinfluence on its growth. Thus, change in salinity had a significant effect onnonspecific immune enzyme activities of juvenile tongue sole and showed cleardifferences among the various tissues.3Effects of acclimation to various environmental salinities on the activities ofseveral key carbohydrate metabolism enzymesEffects of acclimation to various environmental salinities (0,5,10,20and30ppt)in tongue sole for60days on the activities of five carbohydrate metabolism enzymeshexose kinase (HK), pyruvate kinase (PK), the dynamic changes of the six-phosphatedehydrogenase (G6PDH), succinate dehydrogenase (SDH) and malic aciddehydrogenase (SDH) were measured. The results are as follows:(1) The activity ofHK, G6PDH in liver was significantly higher in the freshwater (P<0.05), indicating the increased utilization of glucose under freshwater condition in liver.(2) The highestlevel of PK activity was found in freshwater, which was significantly higher than theother treatments(P<0.05) and the activity of PK at salinity5was also significantlyhigher than that at salinity10-30(P<0.05), which indicated the enhancement ofmuscle glycolysis in freshwater and low salinity conditions.(3) The activity of PK ingill had the minimum level at salinity10, which was significantly lower than that atthe salinity0,20and30(P<0.05). The highest level was found in freshwater, whichwas significantly higher than the activity of salinity5,10and20(P<0.05). Theactivities of SDH and MDH in gills at salinity20and30were significantly higherthan other treatments in low salinity, which showed an enhancement of glycolysis andtricarboxylic acid cycle in gill under the salinity20and30, but glycolysis was onlystrengthened in freshwater conditions.(4)The highest level of HK and PK in kidneywas all found in freshwater condition, which was significantly higher than the othertreatments(P<0.05).The activity of SDH in fresh water and salinity5was significantlyhigher than that of the other treatments (P<0.05). The highest level of MDH wasobtained in freshwater condition, which was significantly higher than the othertreatments (P<0.05). At salinity10and5, the MDH activity in kidney wassignificantly lower than that of other treatments (P<0.05),which indicated that anenhancement both in glycolysis and the tricarboxylic acid cycle cycle in freshwaterconditions.In summary, metabolism had been strengthened in various tissues andorgans of juvenile tongue sole of the low the salinity and freshwater condition. Gillsplayed an important role in the osmoregulation and had an enhancement ofmetabolism enzyme activity at high salinity. Around the isotonic salinity, the activitiesof metabolic enzymes were in lower level due to low metabolic rate. The effect ofsalinity on the metabolism showed clear differences among the various tissues andorgans of non-osmotic regulation studied. |
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