Effects of salinity on iono-osmoregulatory behavior and growth of juvenile Pompano Trachinotus marginatus
The objective of this study was to evaluate the effects of salinity on ionic and osmoregulatory behavior, as well as the growth of juvenile pampo Trachinotus marginatus. An experiment was carried out to estimate the isosmotic point and the plasmatic ionic concentrations of the pampo. The fish (144.7 ± 28.4 g and 19.6 ± 2.0 cm) were acclimated for fifteen days in salinities 4, 8, 12, 16 and 20 and blood samples were collected for analysis of ionic composition and plasma osmolality The isosmotic point was determined by the linear regression between plasma osmolality and water osmolality. In a second experiment, 320 fish (2.14 ± 0.29 g and 5.11 ± 0.33 cm) were randomly distributed in 16 tanks (50L). Each treatment was maintained at salinities 3, 6, 12 and 32 (four repetitions each), equivalent to 25, 50,100 and 267% of the isosmotic point. During the experimental period (28 days), the fish were kept at 28 ° C, pH 8.0, alkalinity 135 mg CaCO3/L and oxygen saturation always above 90%. Oxygen consumption was measured at each salinity. The second branchial arch of 12 fish was Na+/K+ -ATPase collected for analysis of the pampo enzyme activity and was determined to be 357.5 mOsmoles/kg H2O-1, which is equivalent to salinity 13.1. Plasma osmolality, hematocrit, blood glucose, hepatosomatic index and Na+/K+ -ATPase. The isosmotic point of branchial activity was not affected by salinity. In the second experiment, the highest rate of oxygen consumption was observed for fish reared Na+/K+ -ATPase at salinity 3, while branchial activity was significantly higher at this salinity compared to salinities 12 and 32. The concentration of hepatic glycogen in salinity 3 was significantly lower compared to salinity 32. The activity of trypsin in the intestine and the humidity of the muscles did not show significant variation between treatments. The greatest growth was observed in salinities 3, 6 and 12.