Effects of salinity on osmoregulatory parameters of Cobia Rachycentron canadum
The Cobia Rachycentron canadum is the only species of marine fish that has been commercially produced in Brazil. Salinity can influence the development and growth of teleost fish and affect their osmoregulatory processes. This study aims to analyze the effect of salinity on the osmoregulatory parameters of juveniles of Cobia. Juveniles (213.3 ± 6.1 g: 30.2 ± 0.2 cm) were submitted to salinity 3 ‰, 9 ‰, 15 ‰, 21 ‰ and 27 ‰. After 15 experimental days, fish survival was 100% in all treatments, and salinity did not influence fish growth and feed conversion. Plasma osmolality increased according to the increase in salinity in all treatments. According to our results, it was possible to estimate the isosmotic point at 376.5 mOsm / kg H2O,which corresponds to a salinity of 13.4 ‰. The concentrations of Na +, K +, Ca +, Cl- of water and plasma also increased with increasing salinity, and the isoionic points were determined at 188.4, 4.8, 5.18 and 181.4 mEq / L , which corresponds to the salinities of 12.7 ‰, 20.5 ‰, 8.7 ‰ and 7.2 ‰. There was an increase in the number of chloride cells in the gills of fish when exposed to salinities lower than the isosmotic point. Plasma glucose values were lower in treatments below the isosmotic point, indicating a higher metabolic cost of fish in these salinities. Thus, we can conclude that the bijupira is a species with wide osmoregulatory capacity and these results will contribute to future studies of the appropriate ionic composition for the growth of this species in low salinity.These results will assist future studies regarding the appropriate ionic composition for the growth of this species in low salinity.