| dc.description.abstract | In order to improve production efficiency and profitability in tilapia aquaculture, further research is needed to develop methods to improve weight gain, feed utilization, and immune function of these fish. In this regard, numerous studies with several fish species have reported that dietary nucleotides can enhance growth performance, immune responses and disease resistance. Therefore, two feeding experiments were conducted to investigate the effects of a purified nucleotide mix on juvenile Nile tilapia, Oreochromis niloticus.
A basal diet was formulated to contain 34% crude protein from fishmeal and soybean meal. A nucleotide mix containing salts of cytidine, uridine, adenosine, inosine, guanosine, and thymine was supplemented to the basal diet at 0.5, 1 and 2% of dry weight. In the first experiment, three replicate groups of 15 fish were fed the experimental diets. At the end of 8 weeks, weight gain, feed efficiency and survival were computed. Blood samples were analyzed for neutrophil oxidative radical production and plasma lysozyme activity. In the second trial, three replicate groups of 20 fish were fed the same experimental diets. At the end of 4 weeks, blood and kidney samples were analyzed for macrophage extracellular and intracellular superoxide anion production, blood neutrophil oxidative radical production, plasma lysozyme activity, and peripheral blood lymphocyte proliferation. Then, 12 fish per treatment were challenged with Streptococcus iniae, via intraperitoneal injection, and mortality was recorded for 21 days.
Results showed that none of the nucleotide-supplemented diets induced significant (P < 0.05) effects on growth performance. On the other hand, the 0.5% treatment produced significantly (P < 0.05) higher intracellular superoxide anion (O2-) production and both the 0.5 and 1% treatments significantly (P < 0.05) increased lymphocyte proliferation. The disease challenge failed to show significant survival differences among treatments; however, the 2% nucleotide treatment tended to produce higher survivability. Results from both experiments lead to the conclusion that this particular nucleotide mix does not provide marked improvements in growth performance and disease resistance; however, dietary nucleotide supplementation did affect some components of the immune system of Nile tilapia. | en |
