EFFECTS OF A SUMMER TEMPERATURE REGIME REPRESENTATIVE OF A GLOBAL WARMING SCENARIO ON GROWTH AND PROTEIN-SYNTHESIS IN HARDWATER-ACCLIMATED AND SOFTWATER-ACCLIMATED JUVENILE RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

1. Growth, appetite, gross conversion efficiency and protein turnover rates of liver, gills and white muscle were measured in juvenile rainb ow trout chronically exposed (90 days) to soft and hardwater at two te mperatures (ambient, ambient temp. +2 degrees C). The temperature regi me followed that of inshore Lake Ontario over the months of June-Septe mber 1993 as temperature rose from similar to 13 to 24 degrees C. 2. O ver the initial 60 days of exposure, the addition of 2 degrees C to th e ambient temperature increased growth, appetite, gross conversion eff iciency and protein turnover by an average of 16%. However, further ex posure during the period of peak ambient temperatures, led to an avera ge 20% reduction in growth, appetite, gross conversion efficiency and protein turnover. 3. Increased rates of gill protein turnover and argu ably lower rates of growth indicate that the cost of living for a trou t acclimated and maintained in synthetic softwater is higher than that of hardwater fish. In addition, lower appetite in softwater fish sugg est that life in softwater is itself a mild form of environmental stre ss.