Black soldier fly pulp in the diet of golden pompano: Effect on growth performance, liver antioxidant and intestinal health.

Black soldier fly (Hermetia illucens) has been widely researched as a protein source for fish meal replacement in aquaculture, but few studies have focused on its potential as a feed additive for growth and immune enhancement. We conducted a 56-day culture experiment to determine the impact of feed addition of black soldier fly pulp (BSFP, with 86.2% small peptides in dry basis) on growth performance, plasma biochemistry, liver antioxidant levels, intestinal immunity, digestion and microbiota of juvenile golden pompano (Trachinotus ovatus, 5.63 ± 0.02 g). BSFP was added to the basal diet at 0%, 1%, 3%, 5%, 7% and 9% (named Control, BSFP-1, BSFP-3, BSFP-5, BSFP-7, BSFP-9), respectively. BSFP increased the weight gain rate, specific growth rate, protein efficiency ratio and reduced the feed conversion rate of juvenile T. ovatus, the optimal growth performance was reached at BSFP-1, after which a negative feedback phenomenon was observed. Low levels of BSFP upregulated the expression of hepatic antioxidant, intestinal tight junctions, anti-inflammatory related genes and enhanced antioxidant, immune and intestinal digestive enzyme activities, which simultaneously reduced hepatic malondialdehyde and plasma aspartate transaminase and alanine aminotransferase concentrations. However, at BSFP-7, catalase activity was significantly reduced, while NF-κB p65 and pro-inflammatory cytokines transcription was significantly enhanced (P < 0.05). The results suggest that high doses of BSFP addition may damage fish health by inhibiting small peptide uptake, decreasing the activity of antioxidant enzyme and activating the canonical NF-κB pathway. Conversely, low doses of BSFP enhanced intestinal tight junction protein transcription, digestive enzyme activity and immune performance, inhibited pathogenic microbiota, while enhancing liver antioxidant capacity, which was associated with activated Nrf2-Keap1 pathway and suppressed NF-κB pathway, showing its potential as a feed additive to aquafeeds.