Changes in in vitro heart performance in rainbow trout, Salmo gairdneri Richardson, infected with Apatemon gracilis (Digenea).
In vitro, perfused, isolated heart preparations were used to determine the effects of a parasitic infection on the performance of the heart. Increase in preload in the uninfected hearts produced an increase in output flow and power, resulting mainly from increase in stroke volume and little change in heart rate. The heart rate of infected hearts (14.3 beats/min) was slightly, but not significantly, lower than in controls (17.8 beats/min). The cardiac output of infected hearts was 20-40% of that of the healthy hearts. This reduction will, in turn, lead to reduced oxygen transport to the tissues, and so to a reduction in metabolic scope. It is therefore probable that fish carrying this infection will have low food intakes, low growth rates and low activity levels.