Exploring optimum production conditions and nutritional quality of black soldier fly larvae using local bio-wastes for potential use as fish feed in southwest Ethiopia

Abstract

Lack of good-quality and sustainable fish feed is one of the bottlenecks for aquaculture development in Ethiopia. Therefore, the study aimed to explore the optimal production conditions in terms of substrate type, feeding rate, feeding frequency, days for maturity, and nutritional quality of black soldier fly (BSF) larvae using local bio-wastes as potential fish feed in southwest Ethiopia. The study involved two trials. The first experiment assessed the effects of local feed ingredients (poultry manure, brewery waste, and rumen liquor) at different feeding rates (100, 150, 200, and 250 g feed/g larvae/day) on BSF larvae biomass production, growth rate, bioconversion rate, waste reduction efficiency, and days for maturity. The amount of substrate added, total weight, dry weight, initial and final larval biomass and maturation time was recorded. Then the recorded data was statistically analyzed using a two-way ANOVA to establish statistical significance among the groups. Brewery waste was found to be the most effective feed ingredient at 100 g feed/g larvae/day feeding rates, which resulted in the highest larval biomass production (12.2 ± 1.03 g), bioconversion rates of 5.19% to 7.89%, and substrate reduction rates of 40.59% to 46.75%. The second experiment examined the mixed feedstocks with varied feeding regimes (daily, midweek, weekly, and lump sum). The best performance was observed on a mixture of poultry manure (Pm) and brewery waste (Bw) with equal proportions (50:50) applied at lump sum feeding regimes. It produced the highest larval biomass (11.05 g), bioconversion rates of 15.48% to 22.78%, and waste reduction rates of 30.92% to 36.54%. The proximate composition of larvae also varied according to the feed ingredient and feeding strategies; the maximum crude protein (CP) content of 46.5% was shown on larvae reared on poultry manure and brewery waste mixed in equal proportions (50:50), whereas the lowest CP content of 39.7% was observed on larvae reared on rumen liquor. The present study paves the way for a more sustainable and localized approach to fish feed production for aquaculture development in Ethiopia, fostering economic growth, environmental stewardship, and improved food security.