Microwave irradiation and pelleting method affected feed chemical composition and growth performance and feed utilization of sex-reversed Nile tilapia, <i>Oreochromis niloticus</i> (L.)

Abstract

Microwave processing and pelleting methods were assessed to improve aquafeed quality for sex-reversed Nile tilapia. The 2 × 3 experimental feeds were prepared with and without microwave irradiation of ingredients prior to pelleting with either a meat mincer, extruder or steam conditioner followed by a meat mincer. Five feedstuff ingredients, including fish meal, meat and bone meal, soybean meal, broken rice and rice bran, were irradiated separately at optimal times, according to the third-order polynomial regression analysis between in vitro digestibility and microwave irradiation times (r = 0.681–0.942, P < 0.001, n = 42). The prepared feeds were studied for chemical compositions and responses in fish growth performance and feed utilization efficiency. The fish (1.57 ± 0.01 g initial weight) were fed ad libitum for 4 months. All proximate chemical compositions of experimental feeds, except protein, were influenced by microwave processing, pelleting methods or their interaction (P < 0.05). There were no significant effects from either parameter on water quality during the fish trial. Fish fed steamed microwave-irradiated feed, mechanically pelleted with a meat mincer, showed the highest growth performance (weight gain 18.91 ± 0.73 g and specific growth rate 2.15 ± 0.26% day−1) and feed utilization efficiency (feed conversion ratio 1.31 ± 0.05 g feed g gain−1 and protein efficiency ratio 2.27 ± 0.08 g gain g protein−1) compared with the other dietary groups. These findings indicate that microwave irradiation of feed ingredients prior to steam conditioning followed by mincing can improve aquafeed production quality.