Motile Aeromonas Septicemia (MAS) is a significant disease affecting channel catfish (Ictalurus punctatus) in aquaculture settings. The objective of this study was to investigate the impact of nutritional status on the pathogenesis and severity of MAS by comparing pathological findings.
In this study, we used a bath immersion model to simulate the natural route of infection and examined gross and histopathological changes in the stomach, spleen, intestines, and hepatopancreas over time. Channel catfish were divided into four treatment groups: fin-clipped and fed (FCF), not fin-clipped but fed (NCF), fin-clipped and unfed (FCN), not fin-clipped and unfed (NCN). A bacterial challenge using vAh (ALG-15-097) was administered, and fish (n=90) were sampled at 2-, 4-, and 8-hours post-challenge (HPC) for gross and histopathological examination. Key organs including the stomach, spleen, intestines, and hepatopancreas were analyzed for pathological changes. A semiquantitative grading system was used to assess lesion severity, and results were compared between treatment groups. Gross pathological findings revealed that fed groups exhibited more severe external lesions, such as bilateral exophthalmia and hemorrhages around the gills, mouth, and fins, compared to unfed groups. Internally, spleen enlargement and engorged gastric arteries were prominent in fed fish but not in unfed fish. Histopathological examination showed early onset of edema, lymphoplasmacytic infiltration, and epithelial erosions in the stomach and intestines at 2 HPC, progressing to severe hemorrhage and necrosis by 8 HPC. The spleen exhibited severe congestion, edema, and melanosis, particularly in unfed fish, which supports the spleen’s role as a primary immune organ during vAh infection. This study demonstrates that nutritional status significantly influences the distribution and severity of MAS-induced lesions in channel catfish. Fed fish showed more pronounced gastrointestinal lesions, suggesting that postprandial increases in blood flow to the stomach and intestines may facilitate bacterial proliferation. In contrast, unfed fish exhibited more severe splenic damage, indicating that nutrient deprivation may shift the immune response towards splenic sequestration of bacteria. These findings highlight the importance of nutritional status as a modulating factor in the pathogenesis of MAS and underscore the need for further research on the interactions between feeding, immune response, and disease severity in aquaculture settings.