Effects of dietary beta--glucan on growth performance and disease resistance of juvenile hybrid tilapia （Oreochromis aureus♂×Oreochromis niloticus♀）

One thousand hybridization tilapia（Oreochromis aureus♂×Oreochromis niloticus♀） were fed with the basal diet for 7 days. On day 8, five hundreds forty fish[ initial weight（1.84±0.02）g] were selected and randomly divided into 6 treatments with 3 replicates of 30 fish each for the feeding test. beta-（1,3）-glucan was administered to the hybridization tilapia through the diets at six levels（0, 0.5%, 1.0%, 1.5%, 2.0%, 4.0%, respectively） as measured the weight gain rate（WGR）, special growth rate（SGR）, survival rate（SR） and nutrients of muscle. The feed test period was 8 weeks. At the end of the feeding test,the fish were selected, 10 in each replicate randomly for infection test for 7 days. Effects of beta-（1,3）-glucan administration on survival and immune modulations were studied in the fish against the bacterial pathogen, Aeromonas hydrophila by injection. SR was determined at different times after injection（1h、24h、48h、96h. 168h, respectively）. On day 7, test animals injected bacterial pathogen were collected to measure the acid phosphates（ACP） activity and lysozyme（LSZ） activity of head kidney. The results showed that after 56 days of feeding, survival rate ranged from 96.67%--100% and WGR, SGR and SR were not significantly different（P〉0.05） among dietary treatments. The condition factor of the animals fed on 1.5% beta-glucan was significantly higher than the others（P〈0.05）. The muscle protein contents of the fish fed on 2.0% beta-glucan were 3.76% and 3.02% higher than the control and 0.5% group, respectively（P〈0.05）. On day 7 after injection of Aeromonas hydrophila, SR of the control was only 25%, and that of β-glucan supplementation groups were between 60% and 70%. The acid phosphates activity and lysozyme activity of head kidney were significantly higher in the hybridization tilapias fed on 1.5% beta-glucan. Conclusion, in this test, 1.0 beta-1.5% beta-glucan supplementation in the dietary of hybridization tilapia was recommended considering the performance and disease resistance.