Transcriptomic analysis of channel catfish stomach response to Aeromonas hydrophila infection correlated to skin integrity and fed state

This study investigates the immune responses in the stomach of channel catfish (Ictalurus punctatus) under different feeding statuses and physical stress (fin-clipping) after infection with Aeromonas hydrophila. Transcriptomic analysis revealed early activation of Toll-like receptor (TLR) signaling and pro-inflammatory pathways in the fed groups, which led to significant tissue damage as observed in histopathological evaluations. Unfed groups showed delayed immune responses with less tissue damage but higher levels of apoptosis, particularly in the fin-clipped group. Histopathological examination at 2 hours post-challenge (HPC) revealed minimal to moderate edema in the lamina propria and submucosa across all treatment groups. By 4 HPC, mild to moderate edema was noted, accompanied by lymphoplasmacytic and granulocytic infiltration. At 8 HPC, multifocal hemorrhage and erosions in the superficial epithelium, along with moderate to severe transmural edema, were observed. These histological findings, particularly in the fed fin-clipped group, reflect the correlation between immune overactivation and tissue damage leading to higher mortality. Overall design: To determine how feeding and fin-clipping affect the stomach immune response and tissue damage in channel catfish during infection. The experimental design included four treatment groups, each with 25 fish per replicate (6 replicates per group, n=150), for a total of 600 experimental fish including control groups. Treatment was either mock using only sterile media or with Aeromonas hydrophila bacterium. The treatment groups included (1) fish subjected to an immersion challenge without fin clipping and fed on the day of the challenge (2) fish subjected to an immersion challenge with fin clipping and fed on the day of the challenge (3) fish subjected to an oral gavage challenge and fed on the day of challenge and (4) fish subjected to an oral gavage challenge but not fed on the day of the challenge. Fish were sampled at 2, 4, and 8 hours post-challenge. At each time point, 6 fish per treatment group were euthanized, tissues were collected and immediately submerged in RNAlater, and later stored in an ultra cold freezer until processing for RNA sequencing.