Effects of dietary nucleotides supplementation on growth, total haemocyte count, lysozyme activity and survival upon challenge with Vibrio harveyi in pacific white shrimp, Litopenaeus vannamei

The use of soybean meal (SBM) as replacement for fish meal (FM) in diets for Pacific white shrimp (PWS), Litopenaeus vannamei, involves a negative impact on the health of PWS. Dietary nucleotides modulate the immune response; therefore, they might be able to counteract this effect by enhancing PWS immunity. Based on this hypothesis, this study was aimed at evaluating the effects of nucleotide supplementation in PWS receiving diets in which FM had been partially replaced by SBM. A 70-day feeding trial was conducted to evaluate the effects of dietary nucleotides on PWS growth performance, protein levels and retention rate, total hemocyte count (THC) and lysozyme activity. Ten experimental diets were formulated. The control diet included 10% FM and 43% SBM. Another diet was formulated by reducing FM to 5% and by increasing SBM up to 50%. The rest of diets included 0.05 or 0.1% nucleotide supplementation with varying degrees of FM replacement by SBM. A total of 900 PWS post larvae with an average initial body weight of 4.24 +/- 0.03 g were randomly assigned to ten study groups, with six replicates per group and 15 PWS per aquaria tank. After the performance trial, disease resistance was evaluated in a 7-day challenge test with Vibrio harveyi at the consistent concentration of 105 CFU mL(-1). Nucleotide supplementation led to significantly higher THC and lysozyme activity (P < 0.05) and a significantly increased PWS survival in the V. harveyi challenge test (P < 0.05). No significant differences were found between groups regarding growth parameters or protein analyses (P > 0.05). In conclusion, the present study shows a positive impact of nucleotide supplementation on immune response and disease resistance against V. harveyi. Nucleotides could therefore be used as functional dietary ingredients, especially in PWS which receive diets with FM replacement by plant-protein sources.