Transcriptomic analysis of channel catfish intestine response to Aeromonas hydrophila infection correlated to skin integrity and fed state
The study focuses on the intestinal immune responses of channel catfish (Ictalurus punctatus) under various feeding and fin-clipping conditions after infection with Aeromonas hydrophila. Transcriptomic data revealed significant activation of pathogen recognition pathways (TLR signaling and C-type lectins) and pro-inflammatory cytokines, particularly in the fed groups. Histopathological findings at 2 hours post-challenge (HPC) showed minimal to moderate expansion of the lamina propria by edema in the intestines of the treated groups. At 4 HPC, mild to moderate edema with lymphocytes and plasma cells was observed, indicating early immune cell infiltration. By 8 HPC, degenerative changes in the superficial epithelium and hemorrhage were evident, especially in the fed fin-clipped group, which correlates with increased mortality in this group. The unfed groups demonstrated delayed but sustained immune responses, marked by lower histological damage compared to the fed groups. These findings provide insights into how nutritional status and fin-clipping shape the intestinal immune response and tissue damage during infection. Overall design: To determine how feeding and fin-clipping affect the intestinal 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.