Excessive level of dietary insect protein negatively changed growth metabolomic and transcriptomic profiles of largemouth bass(Micropterus salmoides)

Hermetia illucens(HI) meal is a promising substitute for fish meal(FM) in the feeds of farmed fish.However, the impacts of dietary HI meal on largemouth bass(LMB) remain unknown. In this study, we formulated three isonitrogenous and isolipid diets with 0%(HI0, control), 20%(HI20) and 40%(HI40) of FM substituted by HI meal. A total of 270 juvenile largemouth bass with an initial body weight of10.02 ± 0.03 g were used(30 fish per tank). After an 80-day feeding trial, the fish fed with the HI40 diet demonstrated decreased growth performance and protein efficiency ratio(PER), and increased liver oxidative indices and lipid accumulation compared to the control(P < 0.05). Transcriptomic analysis revealed the effects of high dietary HI meal on liver gene expression. Consistent with the reduced growth and disturbed liver oxidative status, the upregulated genes were enriched in the biological processes associated with protein catabolism and endoplasmic reticulum(ER) stress; while the downregulated genes were enriched in cellular proliferation, growth, metabolism, immunity and maintenance of tissue homeostasis. Differential metabolites in the liver samples were also identified by untargeted metabolomic assay. The results of joint transcriptomic-metabolomic analyses revealed that the pathways such as one carbon pool by folate, propanoate metabolism and alpha-linolenic acid metabolism were disturbed by high dietary HI meal. In summary, our data revealed the candidate genes, metabolites and biological pathways that account for the adverse effects of high HI meal diet on the growth and health of LMB.