Fly Prepupae as a Feedstuff for Rainbow Trout, Oncorhynchus mykiss

Fly larvae may provide an effective method to mitigate two large and growing global concerns: the use of fish meal derived from capture fisheries in aquaculture diets and manure management in livestock and poultry facilities. A 9-wk feed trial was conducted to determine whether fly larvae could be used as a partial fish meal and fish oil replacement in rainbow trout, Oncorhynchus mykiss, diets. A trout diet was formulated to contain 40% crude protein and 15% fat. Sixty-seven percent of the protein in the control diet was derived from fish meal, and all the fat was derived from fish oil. Two of the test diets included using the black soldier fly, Hermetia illucens, prepupae, which are 40% protein and 30% fat, as 25 and 50% replacement for the fish meal component of the control diet. The total protein derived from black soldier fly prepupae in these two test diets was 15 and 34%, respectively. A third test diet included using housefly, Musca domestica, pupae, which is 70% protein and 16% fat, as 25% replacement for the fish meal component of the control diet. Data suggest that a rainbow trout diet where black soldier fly prepupae or housefly pupae constitute 15% of the total protein has no adverse effect on the feed conversion ratio of fish over a 9-wk feeding period. In addition, the diet with black soldier fly prepupae permitted a 38% reduction in fish oil (i.e., from 13 to 8%); however, fish fed black soldier fly diets low in fish oil had reduced levels of omega-3 fatty acids in their muscle fillets. The findings from this study suggest that either the black soldier fly or the housefly may be a suitable feedstuff for rainbow trout diets. Extensive research has been done on the potential for manure management in livestock facilities using the black soldier fly, Hermetia illucens (Sheppard et al. 1994, 1998; Newton et al. 2005). It has been estimated that this nonpest fly species can reduce nitrogen and phosphorus waste by up to 75% and the mass of manure residue by 50% in poultry and swine systems (Sheppard et al. 1994, 1998; Newton et al. 2005). The by-product of this bioconversion system is an abundant amount of fly prepupae. These prepupae are approximately 40% 1 Corresponding author. JOURNAL OF THE WORLD AQUACULTURE SOCIETY Vol. 38, No. 1