Effects of dietary cecropin on growth, non-specific immunity and disease resistance of tilapia (Oreochromis niloticus × O. aureus)

An 8-week feeding trial was conducted to evaluate the effect of dietary cecropin on growth performance, non-specific immunity and disease resistance of hybrid tilapia (Oreochromis niloticus × O. aureus). A basal diet was supplemented with 0 (control), 75, 150 and 225 mg kg−1 cecropin to formulate four experimental diets. The results showed that final body weight and specific growth rate obtained with diet 150 mg kg−1 cecropin were significantly higher (P < 0.05) than that obtained with diets 0 and 75 mg kg−1, whereas there was no difference between 150 and 225 mg kg−1. Feed conversion efficiency was improved by increasing the dietary cecropin content (P < 0.05). However, feeding intake was reduced as dietary cecropin increased. Serum lysozyme, alkaline phosphatase, catalase and superoxide dismutase activity were significantly increased with the increased levels of dietary cecropin (P < 0.05), and reached a maximum at level of 150 mg kg−1 cecropin, then those values no longer increased. Moreover, the dietary cecropin supplementation level also exhibited a decrease in the cumulative mortality rates compared with the controls when challenged with Aeromonas veronii. The results suggested that the dietary supplementation of cecropin could improve the growth, non-specific immunity indicators and resistance of hybrid tilapia against A. veronii.