Substituting the Fishmeal With Solid-State-Fermented Black Soldier Fly ( <i>Hermetia Illucens</i> ) Larvae Meal in Gift Tilapia ( <i>Oreochromis Niloticus</i> ) Fry Diet: Effects for Growth Performance, Carcass Composition and Liver Histology <sup>*<

Abstract Replacing fishmeal (FM) with an optimal aquafeed alternative remains a significant challenge. Recent research suggests that insect meal is a potential candidate ingredient for a substitute for fishmeal. Simultaneously, the black soldier fly larvae meal (BM) is an intensively researched insect meal with promising results. However, controversial results and the inability to complete FM substitution prompt further investigation into new techniques. Solid-state fermentation (SSF) has been identified as a cost-effective technique to enhance the efficiency of aquafeed ingredients. Therefore, a nine-week experiment was conducted using fermented black soldier fly larvae meal (FB) to replace FM based on the protein content with 0% (0FB), 35% (35FB), 70% (70FB), and 100% (100FB) in the diet of GIFT tilapia ( Oreochromis niloticus ) fry (0.18±0.01 g/fish) applying SSF. Additionally, FM was entirely replaced by the unfermented black soldier fly larvae meal (UB), including diet (100UB). Results of the weight gain (WG), daily weight gain (DWG), relative weight gain (RWG), and specific growth rate (SGR) of FB-fed fish were statistically higher (P&lt;0.05) than those of UB-fed fish. However, there was a decreasing trend in the growth performance when the FB proportion was increased. Simultaneously, the feed conversion ratio (FCR) and protein efficiency ratio (PER) of all the FB-fed fish were lower than the control. Further, 100UB exhibited reduced values in WG, DWG, and PER, underscoring the positive effect of SSF. Results of the carcass composition analysis showed that the SSF did not adversely affect the carcass crude protein, ash, and fiber contents. However, carcass lipid content decreased statistically (P&lt;0.05) with increasing levels of FB. Histopathological alterations in liver tissues of fish fed with the FB-included diets highlight the importance of screening the rearing surfaces of black soldier fly to ensure feed safety. Overall, the SSF of BM is a viable option for substituting the FM in O. niloticus fry feed without affecting growth performance and feed utilization.