Alkalinity effect in juveniles of Cobia Rachycentron canadum raised in low salinity
Cobia has gained popularity as an excellent candidate for mariculture due to its rapid growth and quality of meat. In the present study, the performance of Cobia juveniles raised in low salinity (3 and 6) with and without the correction of alkalinity (50 and 200 mg CaCO3 / L) in a water recirculation system, plus a control treatment ( salinity 30, and alkalinity 200 mg CaCO3 / L), totaling five treatments. Survival was 100% in all treatments, but the growth parameters (final weight, weight gain, SRG and feed intake) were negatively affected (P <0.05) by the reduction in salinity, when compared with the treatment. control. However, alkalinity seems to affect weight gain and the specific growth rate only of fish kept in salinity 3.Plasma osmolality decreased with decreasing salinity, but only the control showed a significant difference (P <0.05) with the other treatments. The protein and lipid content of the muscle was reduced in salinity 3 treatments, without showing a relationship with alkalinity. The ionic composition of water and plasma is directly related to salinity. The results suggest that R. canadum has a good Elyaline capacity and can be bred for 6 weeks without mortality at low salinities (6 and 3). However, in salinity 3 the maintenance of adequate pH, provided by high alkalinity, has a beneficial effect on fish, improving weight gain and the specific growth rate.