Transcriptome analysis and immune gene expression of channel catfish (Ictalurus punctatus) fed diets with inclusion of frass from black soldier fly larvae

Authors: SANKAPPA, NITHIN - Oak Ridge Institute For Science And Education (ORISE); Lange, Miles; Aksoy, Mediha; Eljack, Rashida; KUCUKTAS, HUSEYIN - Us Fish And Wildlife Service; Beck, Benjamin; Abernathy, Jason

Submitted to: Frontiers in Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2023
Publication Date: 1/9/2024
Citation: Sankappa, N.M., Lange, M.D., Aksoy, M., Eljack, R.M., Kucuktas, H., Beck, B.H., Abernathy, J.W. 2024. Transcriptome analysis and immune gene expression of channel catfish (Ictalurus punctatus) fed diets with inclusion of frass from black soldier fly larvae. Frontiers in Physiology. 14:1330368. https://doi.org/10.3389/fphys.2023.1330368.
DOI: https://doi.org/10.3389/fphys.2023.1330368

Interpretive Summary: The larval waste, exoskeleton shedding, and leftover feed components of the black soldier fly and its larvae makeup the byproduct known as frass. Channel catfish (Ictalurus punctatus) were the subject of a 10-week feed study to assess different dietary amounts of frass inclusion and how this would affect both systemic and mucosal tissue gene expression, especially in regard to growth and immune related genes. Five experimental diets comprising 0, 50, 100, 200, and 300 g of frass per kilogram of feed was fed twice daily for 10-weeks. At the end of the trial, catfish was sampled for gene expression study. Frass from black soldier fly larvae inclusion in formulated diets was found to alter global gene expression and activate innate and adaptive immunity in channel catfish, which has the potential to support disease resistance in this species in addition to demonstrated growth benefits.

Technical Abstract: The larval waste, exoskeleton shedding, and leftover feed components of the black soldier fly and its larvae makeup the byproduct known as frass. Channel catfish (Ictalurus punctatus) were the subject of a 10-week feed study to assess different dietary amounts of frass inclusion and how this would affect both systemic and mucosal tissue gene expression, especially in regard to growth and immune related genes. Fish were divided in quadruplicate aquaria and five experimental diets comprising 0, 50, 100, 200, and 300 g of frass per kilogram of feed was fed twice daily. At the end of the trial, liver, head kidney, gill, and intestine samples were collected for gene expression analyses. First, liver and intestine samples from fish fed either low (50 g/kg) or high (300 g/kg) frass diet were used for transcriptome analysis via Illumina RNA sequencing to determine global differential gene expression when compared to control (no frass) diet. Differentially expressed genes (DEGs) included the upregulation of growth-related genes such as glucose-6-phosphatase and myostatin, as well as innate immune receptors and effector molecules including toll-like receptor 5, apolipoprotein A1, C-type lectin and lysozyme. Based on these initial screenings of low/high frass using RNA sequencing, a more thorough evaluation of immune gene expression of all tissues sampled, and all levels of frass inclusion, was further conducted. Using targeted quantitative PCR panels for both innate and adaptive immune genes from channel catfish, differential expression of genes was identified, including innate receptors (TLR1, TLR5, TLR9, TLR20A), proinflammatory cytokines (IL-1ß type a, IL-1ß type b, IL-17, IFN-', and TNFa), chemokines (CFC3 and CFD), and hepcidin in both systemic (liver and head kidney) and mucosal (gill and intestine) tissues. Overall, frass from black soldier fly larvae inclusion in formulated diets was found to alter global gene expression and activate innate and adaptive immunity in channel catfish, which has the potential to support disease resistance in this species in addition to demonstrated growth benefits.