Abstract:
Prawns have a dietary requirement for nucleotides for optimum growth. Commercial diets and many natural feed ingredients, including fishmeal are high in nucleotides, with guanine and its derivatives contributing the highest proportion of total nucleotide. The aim of this study was to test the role of guanine alone and in combination with other purified nucleotides on growth, survival rate and non-specific immunity of prawns using a supplemented semi-purified diet. Semi-purified diets as basal (or control) and basal diets supplemented with 0.4% GMP, 0.5% GMP and with combinations of 0.4% GMP with 0.1% of each of AMP, CMP, IMP or UMP were used to feed the prawns (initial mean weight of 3.83 ± 0.01 g) for 53 days. Two positive control diets, one comprising the semi-purified diet supplemented with a commercial nucleotide mixture, Optimun at 2.27% (0.5% total nucleotide) and a commercial diet, Lucky Star, were also included. Supplementation levels were chosen based on the optimal total nucleotide content determined in previous trials with the semi-purified diet. Growth rates of prawn (DGC, %/day) were significantly higher in groups of prawn fed diets supplemented with 0.5% GMP, GMP + AMP, GMP + IMP than prawns fed the basal, 0.4% GMP, and GMP + UMP (p ≤ 0.030). THC were highest in groups of prawns fed diets containing GMP + AMP, GMP + IMP, GMP + CMP and the basal diet supplemented with Optimun (32 × 106–33 × 106 cells/mL) and were significantly higher than THC in groups of prawns fed basal diet and diet supplemented with 0.4% GMP alone (~ 26.5 × 106 cells/mL) (p ≤ 0.038). On day 52, concentrations of guanine, adenine, total purine and total nucleotide in prawn diets were highly positively correlated with weight of prawns (p ≤ 0.013), whilst THC was significantly correlated with guanine, total purine and total nucleotide content (p ≤ 0.023). Survival rates of prawns were very high (between 92 and 100%) and did not differ significantly among diet treatments (p = 0.449). Purine nucleotides, especially guanine, appear to be critical for optimal growth of black tiger prawn, Penaeus monodon.