Determination of growth performance, some chronic stress and histological changes of juvenile European sea bass (Dicentrachus labrax) grown in different salinities and temperatures

In this study, the European sea bass (Dicentrarchus labrax) juveniles (? 32 g) were cultured in 3 different temperatures (15, 20, 25°C) and salinity (0, 20, 40?) conditions for 60 days. Growth performance and some blood parameters, as indicators of chronic stress, and histopathological changes that occur in the tissues under these temperature and salinity combinations were investigated.After the temperature and salinity aclimations (2°C or ? 2-5 per day), the highest growth in all the salinity conditions were achieved at 25°C, while the lowest was at 15°C (P<0.001) after the culture period of 60 days. Salinity and temperature×salinity interactions were not found to be effective on growth. Feed conversion ratios (1.1-1.4) were not affected by any combination of salinity and temperature (P>0.05). At the end of the trial it was understood that flesh dry matter, crude protein and particularly crude lipid were significantly affected by temperature, salinity and the interactions of both parameters. Salinity significantly influenced hematocrit values (P<0.001), and in general, all the groups that were grown in fresh water had higher hematocrit levels (36.0-39.5%) compared to other salinity groups (26.2-36.3%). While there was no significant effect of salinity on plasma glucose values (P>0.05), temperature and temperature×salinity interactions significantly affected this parameter (P<0.01). Generally, aspartate aminotransferase (AST) enzyme activity was higher in low-salinity (especially fresh water) and low-temperature groups. Hematocrit, glucose, and AST analyses in the blood have shown that stress was lowest in fish grown at 25°C and 20? salinity. Examinations showed that the groups reared in freshwater had high proportion of gill tissue histopathological damages while these defects were found to be considerably lower in the kidneys. These distortions further increased at low temperatures.