Effects of dietary cecropin on growth, non‐specific immunity and disease resistance of tilapia ( O reochromis 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 ( O reochromis 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 A eromonas 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 .