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

Abstract

Microwave processing and pelleting methods were assessed to improve aquafeed quality for sexreversed Nile tilapia. The 2 X 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 thirdorder 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.