Effects Of Low-salt Stress On The Growth, Physiological And Biochemical Indexes Of Juvenile Lateolabrax Japonicus

1 Effects of salinity on the growth and biochemical composition of juvenile Lateolabrax japonicusThe growth rate, survival rate and biochemical composition of juvenile Lateolabrax japonicus were examined under the salinities of 15.00,12.50,10.00,7.50,5.00,2.50 and 0.00. Experimental results showed that gain weight and survival rate were significantly affected by salinities, the highest growth rate and the higher survival rate were found at the salinity of 7.50. In the biochemical composition, the contents of protein, lipid and ash decreased with the salinity decrease, but the moisture content increased with the salinity decrease.2 Effects of salinity on the fatty acids composition and contents of juvenile Lateolabrax japonicusUndert the salinities of 15.00, 12.50, 10.00, 7.50, 5.00, 2.50 and 0.00, the change of the fatty acids composition and contents of juvenile Lateolabrax japonicus were analyzed by methods of gaschromatography(GC). Experimental results showed that fatty acids contents changed in different salinities. The differences in total saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) weren't significant. The total polyunsaturated fatty acids (PUFA) content increased with the salinity decrease, especially in EPA(C20:5n-3, eicosapentaenoic acid), DHA (C22:6 n-3, docosahexaenoic acid), AA(C20:4n-6, arachidonic acid). The lower the salinity, the higher the content of n-3 polyunsaturated fatty acids (n-3 PUFA).But the lower the salinity, the lower the content of n-6 polyunsaturated fatty acids (n-6 PUFA).3 Effects of salinity on the composition and contents of the amino acids of juvenile Lateolabrax japonicusThe changes of the amino acid profiles of juvenile Lateolabrax japonicus were analyzed with Post-column Derivatizer technique together with HPLC under different salinities of 15.00, 7.50 and 0.00. The results showed that the contents of the total amino acids under different salinities increased gradually and the differences were not significant in this experimentation. The total essential amino acid (EAA) decreased at the salinity of 15.00, but the total essential amino acid (EAA) increased at the salinity of 7.50 and 0.00. The differences of the total essential amino acid were significant under different salinities of 15.00, 7.50 and 0.00. In addition, the differences of the total of non-essential amino acids and every non-essential amino acid except proline were not significant under different salinities.4 Effects of salinity on digestive enzyme activities of juvenile Lateolabrax japonicusIn order to research the effects of salinity on digestive enzyme activities of juvenile Lateolabrax japonicus, the activities of digestive enzyme of juvenile Lateolabrax japonicus were measured at 0d, 3d, 6d, 9d, 16d and 23d under different salinities of 15.00, 7.50 and 0.00. The results are listed as follows. Under different salinities of 15.00, 7.50 and 0.00, the activities of pepsin, trypsin and amylase of juvenile Lateolabrax japonicus had the same change which tended to increase on the whole.But the differences in the digestive enzyme activities weren't significant. At the end of the experimentation, it was highest that the activity of pepsin of juvenile Lateolabrax japonicus at the salinity of 15.00. The activity of trypsin was the highest at the salinity of 0.00 and the activity of amylase was the highest at the salinity of 7.50. The effects of the low-salt stress on digestive enzyme activities of juvenile Lateolabrax japonicus were significant.5 Microscopical observation on the gill structure of juvenile Lateolabrax japonicus under different salinitiesBy use of the technology of paraffin section and photomicrography, the gill structure of juvenile Lateolabrax japonicus was observed under the different salinities. The results showed that the number and size of chloride cells in filament epithelia increased remarkably. On the lamellae of these fish, chloride cells were generally centralizing to the base of lamellae. Moreover, the number of mucous cells is more. In contrast to the salinities of 15.00 and 0.00, lamellae were narrower and the distribution, structure and number of chloride cells were undiversified significantly at the salinity of 7.50. At the salinity of 0.00, lamellae were broaden and arrayed closely. A few chloride cells were present on the base of lamellae. The gills structure of juvenile Lateolabrax japonicus adapte themselves to the change of aqueous salinity. The structure and number of chloride cells were acclimatized to environmental changes.