Growth and metabolic parameters of common snook juveniles raised in freshwater with different water hardness

- Usually there is mortality when common snook are transferred from seawater to freshwater.
- Transference of common snook to water with hardness of 100 mg CaCO3 L− 1 or higher increases survival.
- Plasma osmolality was not affected by transference to freshwater at any hardness tested.
- Common snook presented best growth at hardness of 100 mg CaCO3 L− 1 in freshwater.

The adaptation of common snook Centropomus undecimalis to low salinities and freshwater has being widely studied, but the definition of the best water hardness levels may facilitate the adaptation and growth of this species in freshwater. Consequently, the aim of this study was to evaluate survival, growth and metabolic parameters (blood glucose and osmolality and lactate in plasma and tissues) of common snooks raised in freshwater with different water hardness levels. In an acute experiment, juveniles were transferred from seawater 35 ppt to seawater 35 ppt (control) and freshwater at 20, 100, 250, 500 or 1000 mg CaCO3 L− 1. Mortality after 96 h was 100, 79.17, 58.33, 4,17 and 50%, respectively. In another experiment juveniles (initial weight 10.9 ± 1.5 g) were maintained for 60 days in water hardness of 100, 500 or 1000 mg CaCO3 L− 1 or seawater (control). No mortality was observed in this experiment. The best weight gain, specific growth rate and feed intake in freshwater (values not significantly different from seawater) was observed in common snooks kept at 100 mg CaCO3 L− 1. Blood and hepatic glucose did not differ significantly between treatments. Muscle glucose levels were significantly lower in fish kept at 100 and 1000 mg CaCO3 L− 1 than the other treatments. However, lactate levels were higher in the muscle of common snooks kept at 100 to 500 CaCO3 mg L− 1 and lactate in plasma was higher in those maintained at 1000 mg CaCO3 L− 1. Plasma osmolality was not affected significantly by treatments. In conclusion, 100 mg CaCO3 L− 1 is the best water hardness to raise common snooks in freshwater.