Effects of defatted black soldier fly pupal meal on growth performance and nutrient utilization of juvenile blue swimming crab (Portunus pelagicus) cultured in a condo system

Abstract

This study evaluated defatted black soldier fly (Hermetia illucens) pupal meal (BSFPM) as an alternative protein ingredient in diets for juvenile blue swimming crab (Portunus pelagicus), with emphasis on protein digestibility, growth, feed utilization, physiological responses, and body composition. In vitro protein digestibility of different black soldier fly preparations was first assessed using hepatopancreatic enzyme extracts from blue swimming crab. A subsequent 90-day feeding trial compared five formulated diets containing 0, 20, 30, 40, or 50% BSFPM and a trash fish reference treatment. BSF pupa meal showed high in vitro protein digestibility (90.40%), comparable to fishmeal (89.75%). Dietary BSFPM produced a non-linear growth response. Crabs fed the fishmeal-based control diet showed the greatest overall growth, whereas growth was reduced particularly at 30 and 40% BSFPM. At 50% inclusion, however, specific growth rate (4.81% day⁻¹) approached that of the control (4.98% day⁻¹). Survival was unaffected by dietary treatment. Feed conversion ratio increased numerically from 1.46 in the control to 5.13 at 50% BSFPM, although differences among the formulated diets were not significant. Dietary BSFPM also altered hemolymph biochemical variables, carapace coloration, and whole-body composition. These findings demonstrate that the high in vitro digestibility of BSFPM does not necessarily translate into equivalent growth and feed-use efficiency in vivo. Defatted BSF pupal meal can provide digestible protein for juvenile P. pelagicus, but optimization of dietary nutrient balance and feed efficiency is required before a specific inclusion level can be recommended for practical feeds.