Consumption of non-native rainbow smelt (<i>Osmerus mordax</i>) is associated with changes in the heart morphology of wild lake trout (<i>Salvelinus namaycush</i>)

The heart is an essential organ for survival and reproduction across all animals. In particular, salmonine fishes display vast variability in heart morphology across and even within populations, which often reflects their functional requirements for cardiac output and aerobic capacity. However, changes in heart morphology are not always adaptive, and other factors such as diet can influence heart morphology. A growing concern is the consumption of the thiamine (vitamin B 1 )-degrading enzyme thiaminase found in some prey species such as rainbow smelt ( Osmerus mordax (Mitchell, 1814)). Here, we investigate the association between rainbow smelt consumption and heart morphology in wild lake trout ( Salvelinus namaycush (Walbaum in Artedi, 1792)) found in the Sudbury Basin (Ontario, Canada). We found that rainbow smelt consumption is associated with increases in ventricular mass, reductions in ventricular fluid content, and alterations in the allometry of myocardia. We discuss the potential impacts of these changes in heart morphology for the conservation of the species.