Response of rainbow trout (Oncorhynchus mykiss) to simulated climate warming and sublethal ammonia

Abstract

<p>The earth's temperature is predicted to increase roughly 1-5°C over the next 50 years, against a backdrop of increasing environmental pollution. This is expected to have a profound effect on fish, organisms whose life processes are intimately linked to their environmental temperature. The present investigation quantified, in the laboratory, the basic bioenergetic, physiological, and toxicological responses of juvenile rainbow trout (Oncorhynchus mykiss) to a naturally fluctuating water temperature cycle (characteristic of inshore Lake Ontario), and to this cycle +2°C (simulated warming scenario) in the presence or absence of 70μM total ammonia (a common environmental pollutant).</p> <p>This thesis provides concrete evidence that small temperature increase and low-level environmental pollution substantially alter the growth, feeding, physiology, and metabolism of juvenile rainbow trout, especially at the temperature extremes: positively during minimum winter temperatures (≈42% increase in growth rate and energy conversion efficiency), and negatively during summer maximum temperatures (≈38% decrease in growth rate and 11% decrease in conversion efficiency). Their responses to sublethal ammonia can be quite different based on seasonal temperature, but within the optimal temperature for growth (16-20°C), +70 μM ammonia appears to stimulate nitrogen retention and metabolism. Significant decreases during late summer in the activity of some of the enzymes involved in nitrogen metabolism indicated that protein systems of juvenile trout are potentially sensitive to the combination of chronic temperature increase in combination with sublethal ammonia pollution. An important factor influencing the responses of trout to a warmer, more polluted environment is nutritional status (i.e., 5-7 fold increase in oxygen consumption per unit protein growth). It is apparent from this investigation that juvenile trout in a better nutritional state will exhibit at least some adaptation to chronic temperature increase. However, this adaptation, either alone or in the face of sublethal ammonia pollution, may require a significant increase in the overall cost of living (10-17%).</p>