Introduction: The increasing global demand for animal protein requires sustainable ingredients that reduce dependence on fishmeal. Black soldier fly (Hermetia illucens) larvae meal is a promising alternative, but information on its use for paco (Piaractus brachypomus) juveniles is limited. This study evaluated the apparent digestibility, growth performance and blood biochemical profile of paco fed diets in which fishmeal was partially or totally replaced by H. illucens larvae meal.

Methods: An apparent digestibility trial was conducted for 6 weeks in Gelph-type collectors using 9 fish fed control, fishmeal and H. illucens meal test diets. A 60-day growth trial was carried out at the Pucayagro fish farm, located in the San Martín region, Peru, with 4 replicate tanks per treatment and 20 fingerlings per tank. Experimental diets replaced fishmeal with insect meal at 0%, 30%, 60% and 100%. At the end of the growth trial, blood samples were collected for analysis of triglycerides, cholesterol, hepatic enzymes, glucose and total protein.

Results: H. illucens larvae meal showed high apparent digestibility, particularly for ether extract (97%) and crude protein (88%). Fish fed the 30% replacement diet achieved weight gain comparable to the control, whereas 60% and 100% replacement reduced growth. Diets containing insect meal increased the amount of plasma triglycerides and induced a progressive reduction in cholesterol with an increasing replacement level. Activities of AST and ALT rose at higher inclusion levels, while glucose and total protein levels remained within physiological ranges.

Conclusions: Dried H. illucens larvae meal can replace up to 30% of dietary fishmeal in paco fingerlings without compromising growth or key blood biochemical indicators. Higher replacement levels negatively affect performance and may challenge hepatic function, highlighting 30% fishmeal substitution as a practical upper limit under the present conditions.