Chronic exposure of rainbow trout (Oncorhynchus mykiss) to simulated climate warming and sublethal ammonia: a year-long study of their appetite, growth, and metabolism

This study was conducted to assess, over the thermal cycle of an entire year, the effects (on appetite, growth, and metabolism) of a chronic small temperature increase (+2°C) and sublethal ammonia (70 µmol ·L-1) on rainbow trout (Oncorhynchus mykiss). Juvenile rainbow trout ( approx 11 g initially) were exposed for 14 months to four treatments: the natural water temperature cycle of the inshore region of Lake Ontario, this cycle +2°C to simulate a global warming scenario, and these temperature cycles in the presence of an additional 70 µmol total ammonia ·L-1 (NH3 range: 0.005-0.013 mg ·L-1). The additional +2°C substantially increased appetite over winter, significantly elevating specific growth rates. These gains were lost, however, over summer due to suppression of appetite and growth at high temperature. Ammonia alone tended to elevate growth, but the combination of +2°C and ammonia resulted in a general decrease in the activity of enzymes involved in nitrogen metabolism (alanine aminotransferase, aspartate aminotransferase, glutamate dehydrogenase, and glutamine synthetase). These results document the dramatic influence of a +2°C warming scenario on the growth and feeding metabolism of juvenile rainbow trout. Moreover, the data indicate that a chronic small temperature increase, together with low-level ammonia pollution, substantially alters protein dynamics, and hence growth, in juvenile freshwater fishes; juvenile rainbow trout without thermal refuge will experience an increase in t a warmer, more polluted environment.