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 entir e year, the effects (on appetite, growth, and metabolism) of a chronic small temperature increase (+2 degrees C) and sublethal ammonia (70 m u mol.L-1) on rainbow trout (Oncorhynchus mykiss). Juvenile rainbow tr out (approximate to 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 degrees C to simulate a global warming scenario, and these temperature cycles in the presence of an addition al 70 mu mol total ammonia.L-1 (NH3 range: 0.005-0.013 mg.L-1). The ad ditional +2 degrees C substantially increased appetite over winter, si gnificantly elevating specific growth rates. These gains were lost, ho wever, over summer due to suppression of appetite and growth at high t emperature. Ammonia alone tended to elevate growth, but the combinatio n of +2 degrees C and ammonia resulted in a general decrease in the ac tivity of enzymes involved in nitrogen metabolism (alanine aminotransf erase, aspartate aminotransferase, glutamate dehydrogenase, and glutam ine synthetase). These results document the dramatic influence of a +2 degrees C warming scenario on the growth and feeding metabolism of ju venile rainbow trout. Moreover, the data indicate that a chronic small temperature increase, together with low-level ammonia pollution, subs tantially alters protein dynamics, and hence growth, in juvenile fresh water fishes; juvenile rainbow trout without thermal refuge will exper ience an increase in t a warmer, more polluted environment.