As the demand for marine ingredients outpaces the supply of these commodities, alternative protein ingredients are necessary to support continued expansion of the aquaculture industry. In addition, there is an increasing consumer demand for the inclusion of low-impact raw materials that can access underutilized waste streams from other value chains. Black soldier fly larvae (BSFL) meal is one such ingredient with the potential to satisfy both the high-quality nutrient requirements to replace fishmeal in aquafeeds and satisfy the modern consumer sustainability demands. In the current trial, BSFL meals were produced by growing BSFL on either a commercial 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 supplemented in the diets of juvenile red drum to replace Special Select™ menhaden fishmeal (MFM) at rates of 0, 50, 75, and 100% on a dry-matter 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 comparative 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 in place of MFM presented numerically decreasing 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 while higher replacement (75 and 100%) is suboptimal based on reduced growth and overall health indices.