Enhancement of growth and feed utilization of the European sea bass (Dicentrarchus labrax) fed supplementary dietary salt in freshwater

The effects of increased dietary sodium chloride supplement on growth, feed efficiency (FE), feed dispensed rate and fillet composition and morphological indices of European sea bass (initial weight of 4.9 g) were investigated in freshwater using five different levels of supplemental salt (0 (control diet, with no salt supplemented), 1%, 3%, 5% and 9% of diet). Over the experimental period of 50 days, the final weight of dietary salt (DS) groups was found to be approximately 19% higher than the control group. The final weight, specific growth rate and FE were greatest at the moderate level (1-5%) of salt supplementation. Optimum level of DS inclusion was calculated as 3%. Feed efficiency was significantly enhanced with increasing salt level up to 5%. A negative relationship between daily feed intake and FE (r(2)=0.66) was observed. The average muscle ratio (MR) in groups fed 1-5% supplemented salt was around 51.4% whereas fish receiving control and 9% salty diets had 5.3% lower MR (48.7%) (P<0.05). However, no significant effects of salt inclusion were found on viscera or hepatosomatic indices. Muscle ash and dry matter content slightly rose with increasing DS in the diet, but with no statistical difference (P>0.05). Similarly, no significant changes were observed in either muscle protein or lipid content among the groups (P>0.05).