Differences in body condition and hepatic cellular metabolism among distinct populations of cestode-infected pumpkinseed sunfish (Lepomis gibbosus)

Host populations can vary in the prevalence and intensity of their parasites, which may influence the impacts of infection on host physiology and health. Parasite-induced effects on hosts may be due to underlying changes in cellular energy metabolism, predominantly driven by the mitochondria. However, limited research has been conducted on understanding variation in host–parasite interactions across populations. We sampled three wild populations of pumpkinseed sunfish ( Lepomis gibbosus (Linnaeus, 1758)), two of which are infected by cestodes, to study correlations among infection intensity, host body condition, and key metabolic enzyme activities in liver tissue. In both infected populations, cestode infection was associated with reduced hepatic lipid metabolism and increased hepatic lactic fermentation. Interestingly, Lake Cromwell fish showed a decrease in body condition, electron transport system activity, and antioxidant activity with cestode intensity, whereas the contrary was observed for Lake Long fish. This suggests that Lake Long fish could be boosting their immune system and food intake to better tolerate infection, unlike Cromwell fish. This study not only highlights how different populations can vary in their response to parasite infections but also the importance of accounting for infection when studying animal physiology.