Food waste-based pellets for feeding grass carp (Ctenopharyngodon idellus): Adding baker's yeast and enzymes to enhance growth and immunity.

Protein rich food waste could be used as raw materials for making fish feed pellets, which would diminish the volume of dumped waste into landfills. This study investigated the use of food waste (FW) based pellets composing of 75% food wastes derived from plant materials (cereals, fruit and vegetables) supplemented with yeast and the mixture of bromelain and papain to feed grass carp (Ctenopharyngodon idellus). Generally, improved growth performance (in terms of feed conversion ratio, protein efficiency ratio and relative weight gain) was observed in the diet groups supplemented with yeast (Saccharomyces cerevisiae). The most optimal dose was 25 g/kg yeast with enzymes (bromelain and papain, at the ratio of 1:1) and protein utilization was enhanced. Fish immunity was also stimulated, which indicated by the higher nitroblue tetrazolium and bactericidal activities. Moreover, resistance against Aeromonas hydrophilia was enhanced. It is envisaged that food waste could be widely used as feeds for culturing herbivorous fish and adding supplements such as baker's yeast and enzymes will further enhance the feed conversion ratio and fish immunity.