Evaluation of parasitic contamination and effects on estimates of mitochondrial enzymatic activities in infected fish livers

Parasites can impair host performance including alterations to host metabolism. Since mitochondria are responsible for cellular energy production, it is likely that disruptions in cellular metabolism contribute to changes at the whole-organism level. However, studies investigating parasite-induced alteration do not take the presence of parasites in the target tissues into account. It is critical to assess the potential interference of parasite contamination in biochemical assays of host tissues to have confidence in the results measured from infected animals. Our objectives were to (1) develop and validate a protocol for extracting parasites from hepatic tissues of pumpkinseed sunfish ( Lepomis gibbosus Linnaeus, 1758) infected with cestodes ( Proteocephalus ambloplitis Leidy, 1887) and (2) to evaluate the extent to which parasite contamination impacts estimates of enzyme activities. We tested five treatments: uninfected lake, infected livers that were cleaned, infected livers with parasites (repopulated), uninfected livers from an infected lake and parasites alone. We compared the activity of metabolic enzymes among groups and assessed contamination through PCR tests. Enzyme activities of cleaned livers and repopulated livers were similar despite PCR tests revealing contamination in cleaned livers suggesting that studying the organs of heavily parasitized individuals is possible. Nevertheless, we recommend that our cleaning protocol is applied to infected organs.