Effects of Salinity on Growth, Muscle Biochemical Components and Antioxidant Resistance of Planiliza haematocheilus

This study evaluated the effects of different water salinities (0, 10, 20 [control], 30, and 40; Practical Salinity Scale, dimensionless) over 56 days on growth performance, muscle biochemical composition, and antioxidant responses in serum and liver of Planiliza haematocheilus. After one-week pre-acclimation at 20, juveniles were directly transferred to the experimental salinities; thus, all groups except the 20 control experienced acute salinity transfer followed by 56-day exposure. Therefore, acute transfer stress and subsequent salinity exposure were confounded and could not be separated in this design. Survival was highest at 20 and lowest at 0. Weight gain rate and specific growth rate peaked at 30 and were lowest at 0. Under this direct-transfer protocol, the optimal salinity range for growth and survival was approximately 20–30 for these ~93 g juveniles. Hepatosomatic index differed significantly among salinity groups. Muscle moisture content was negatively correlated with salinity. Crude protein content was highest in the salinity-40 group, whereas crude fat was highest at 20 and lowest at 0; ash content did not differ significantly among treatments. Superoxide dismutase (SOD) activity in serum and liver showed no clear trend with salinity, but most groups differed significantly from the control. Liver SOD activity was highest at 10 and lowest at 30. Serum catalase (CAT) activity did not differ significantly among salinity groups, whereas liver CAT activity tended to decrease and then increase with rising salinity. Salinity had limited effect on serum malondialdehyde (MDA) content, except for a peak at 40, whereas liver MDA content decreased with increasing salinity and was significantly higher in the low-salinity groups. These results indicate that, under the direct-transfer protocol, P. haematocheilus juveniles (initial weight ~93 g) pre-acclimated to 20 and then directly transferred showed optimal growth and survival at 20–30, and that liver antioxidant parameters may serve as sensitive biomarkers of salinity stress. However, because acute transfer stress was confounded with subsequent 56-day salinity exposure, these findings are specific to this direct-transfer protocol and developmental stage and should not be extrapolated to gradual acclimation protocols or smaller juveniles.