The continued growth of aquaculture necessitates sustainable alternatives to fishmeal and fish oil. Nutrient-rich waste streams are increasingly being explored as substrates for insect production, with black soldier fly larvae (BSFL) emerging as a promising source of high-quality meals that can partially replace marine ingredients and support sustainability goals. 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 50ºC, processed into meals and then evaluated for nutrient digestibility with red drum. Subsequently, a comparative feeding trial was conducted with sub-adult red drum in which Special Select™ menhaden fishmeal (MFM) was replaced by the insect-based meals. 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 formulations in which BSFL reared on the Gainesville (G50), red drum (RD50), and tuna (T50) substrates replaced MFM at 50% on a digestible-protein basis. This study was designed as a continuation of prior work with early-stage red drum, where insect-based meals were shown to effectively replace up to 50% of MFM without adverse effects on growth performance.
Triplicate groups of 22 juvenile red drum (94.8±1.7 g initial weight) were cultured in 12, 1200-L tanks fashioned as a recirculating aquaculture system. Fish were fed to apparent satiation twice daily for the duration of the 8-week feeding trial. At the end of the trial, no statistical differences in growth, feed efficiency, and survival were observed for any dietary treatment (Table 1). On the other hand, the hepatosomatic index values significantly increased with the inclusion of insect-based meals to the experimental diets (Table 2). Additionally, G50 and T50 diets promoted a significant reduction in the intraperitoneal fat values when compared to the Ref and RD50 groups. No significant differences were observed for fillet yield and fillet and liver proximate composition. The current study suggests that 50% replacement of fishmeal using BSFL reared on unique seafood processing byproducts is feasible. Additional long-term investigations should further evaluate the impacts of these insect-based products on liver health and body lipid distribution.