Background: Non-antibiotic strategies are needed to limit losses caused by Aeromonas hydrophila in aquaculture. Black soldier fly, Hermetia illucens, prepupal hexane extract (BSF-HE) may modulate inflammatory responses, but its concentration-specific effects during bacterial challenge remain unclear.
Objectives: To determine the effects of dietary BSF-HE on traf6, tnfa and nos2b transcript abundance in A. hydrophila-challenged zebrafish.
Methods: Adult zebrafish (Danio rerio) were assigned to three replicate aquaria per group (30 fish/aquarium): an uninfected control, an infected control, and four infected groups fed BSF-HE at 500, 1,000, 2,000 or 4,000 mg/kg feed for 30 days. On day 31, fish were exposed for 48 h by bath to approximately 10⁷ CFU/mL A. hydrophila. Mortality was monitored. On day 33, one surviving fish per aquarium was sampled, yielding three aquarium-level biological replicates per group. Transcript abundance was quantified by qPCR using 2−ΔΔCt normalized to actb1. Log₂-transformed fold-change values were analyzed by one-way ANOVA and Tukey’s test.
Results: Mean abundance of all three transcripts was higher in the infected control than in the uninfected control, but only traf6 differed significantly. BSF-HE produced a concentration-specific, non-monotonic pattern. At 500 mg/kg, traf6 was similar to the uninfected control, whereas tnfa and nos2b were lower than both controls. At 1,000 mg/kg, traf6 was lower than both controls, while tnfa and nos2b did not differ from the infected control. At 2,000 mg/kg, tnfa exceeded the infected control, traf6 was lower than the infected control but higher than the uninfected control, and nos2b was lower than the infected control. At 4,000 mg/kg, all three transcripts were low. Available mean mortality counts were 0, 13, 6, 7 and 9 for the uninfected control, infected control, 500, 1,000 and 2,000 mg/kg groups, respectively; the 4,000 mg/kg mortality summary was unavailable.
Conclusions: Dietary BSF-HE was associated with concentration-specific, non-monotonic transcriptional changes rather than a simple dose-response pattern. Because bacterial burden, functional immune measures, protein-level confirmation and complete mortality data were unavailable, reduced transcript abundance should not be interpreted as improved immunity, anti-inflammatory efficacy or protection. Further studies integrating molecular, functional and survival endpoints are warranted.