Examining the dietary effect of insect meals on the innate immune response of fish: A meta-analysis

Insect meal inclusion in aquaculture feed has received increased interest as a sustainable alternative to fishmeal and recent evidence has shown additional effects on modulating the immune response. However, lack of effects of insect meal on fish immunity in a few studies have put these beneficial effects into question. The objective of this meta-analysis was to summarize the effects of fishmeal replacement with insect meal on the innate immune response of several fish species based on differential gene expression via qPCR. A systematic literature search was conducted using online databases including Web of Science and ScienceDirect that found 197 studies as of August 2023, however only 20 studies met the criteria of high-quality studies focused on the immune response of fish and were included in this meta-analysis. The most studied insect meal was from black soldier fly, followed by yellow mealworm, and the most commonly analyzed tissue was the liver, followed by the intestine. The effect of fishmeal replacement with insect meal on fish immune responses were examined using a mixed model, with study as the random effect. This meta-analysis found a non-linear (quadratic) relationship (P = 0.017) between immune gene expression fold change and the level of fishmeal replacement with insect meal. Based on the fitted quadratic curve, a 40 % replacement of fishmeal with insect meal resulted in the highest upregulated immune response in fish. Fish taxonomic family was also found to have an effect (P = 0.004) on immune gene expression, where the taxonomic family Moronidae was more affected, with an average fold change of 2.783 (+/- 0.325). Other variables examined, including the insect type, tissue analyzed, dietary crude protein level, did not affect the immune response (P > 0.05). This meta-analysis also found that dietary lipid had a significant correlation with immune gene expression, and should be taken into consideration in future studies and meta-analyses. These findings are impactful since they provide evidence for the optimal dietary replacement level of insect meals required to significantly affect the innate immune response across several fish species.