Dietary sodium chloride effect in Nile tilapia fed with fish meal-free diets

Aim of study: To evaluate the effect of the dietary NaCl level for Nile tilapia fingerlings.Area of study: Palotina sector of Federal University of Paraná, in southern Brazil.Material and methods: An experiment was carried using 750 Nile tilapia fingerlings (4.61 ± 0.09 g) distributed in 30 1,000-L circular tanks in a completely randomized design with six treatments and five replicates. NaCl was added to extruded fish meal-free diets at 0.0, 2.5, 5.0, 7.5, 10.0 and 12.5 (g/kg). After the experimental period, fish were submitted to a 24 h-fast and weighed. All data were submitted to an analysis of variance and Tukey’s test followed by Levene’s test and regression test, using the Statistica 7.0® software package.Main results: Fish fed the NaCl-free diet presented better growth performance (p<0.05) compared to the other diets. Linear decrease effects on final weight (y = 50.1754 – 0.1672x, r2 = 0.6984), specific growth rate (y = 45.5418 – 0.1688x, r² = 0.6966), weight gain (y = 4.9465 – 0.008x; r² = 0.6886) and apparent feed conversion (y = 0.7113 + 0.0043x; r² = 0.7655) were noted. Efficiency and apparent protein retention were better in the NaCl-free diet (p<0.05). Significant differences (p<0.05) were observed for fillet fat and crude protein content. Increasing NaCl levels led to significant decreases (p<0.05) in Nile tilapia fingerling protein efficiency rates (y = 3.7804 - 0.0116x; r² = 0.6549).Research highlights: Thus, NaCl should not be included in fish meal-free diets for Nile tilapia fingerlings.