There is a continuing need to develop and evaluate alternative protein and lipid feedstuffs as potential substitutes for traditional marine ingredients (fishmeal and fish oil) to support further expansion of aquaculture. In addition, there is increasing interest in utilizing nutritionally valuable raw materials from underutilized waste streams. Cultivation of black soldier fly larvae (BSFL) holds the potential to produce meals with high-quality nutrients to partially replace fishmeal and fish oil as well as satisfy modern sustainability demands. In the current study, BSFL meals were produced by growing BSFL on either a commercial (Gainesville) house fly substrate or one in which 75% of the commercial substrate was replaced with either processing byproducts (filleted carcasses) from red drum or tuna on an equal-weight basis. The BSFL raised on the various substrates were dried at 60C, processed into meals and then evaluated for nutrient digestibility with sub-adult red drum. Subsequently, a comparative feeding trial was conducted with juvenile red drum in which Special Select™ menhaden fishmeal (MFM) was replaced at rates of 0, 50, 75, and 100% on a digestible-protein basis. The reference (Ref) diet was composed of practical ingredients including MFM at 15% of dry weight to provide digestible protein at 36% of dry diet. The experimental diets included those in which BSFL reared on the Gainesville substrate replaced MFM at either 50% (G50) or 75% (G75), BSFL reared on red drum processing byproduct replaced MFM at 50% (RD50) or 75% (RD75), and BSFL reared on tuna processing byproduct replaced MFM at 50% (T50), 75% (T75), or 100% (T100).
Quadruplicate tanks of 17 juvenile red drum (~5.0 g initial weight) were cultured in 24, 38-L aquaria fashioned as a recirculating aquaculture system. Fish were fed to apparent satiation twice daily based on a percentage of body weight, which was adjusted weekly for the duration of the 6-week feeding trial. At the end of the trial, no statistical differences in weight gain were observed for any dietary treatment; however, higher dietary inclusions of BSFL reared on either seafood processing byproduct tended to decrease percentage weight gain (Figure 1) and feed efficiency. Similarly, body condition indices and muscle yield expressed as a percentage of body weight were not statistically different; however, a numerical increase in hepatosomatic index was observed in fish fed diets in which BSFL reared on seafood processing byproducts replaced 75 and 100% of dietary fishmeal. The current study suggests that 50% replacement of fishmeal using BSFL reared on unique seafood processing byproducts is feasible. Additional investigations are underway to further evaluate these BSFL meals.