Effects of a summer temperature regime representative of a global warming scenario on growth and protein synthesis in hardwater- and softwater-acclimated juvenile rainbow trout (Oncorhynchus mykiss)

1. 1. Growth, appetite, gross conversion efficiency and protein turnover rates of liver, gills and white muscle were measured in juvenile rainbow trout chronically exposed (90 days) to soft and hardwater at two temperatures (ambient, ambient temp. +2°C). The temperature regime followed that of inshore Lake Ontario over the months of June-September 1993 as temperature rose from ∼13 to 24°C. 2. 2. Over the initial 60 days of exposure, the addition of 2°C to the ambient temperature increased growth, appetite, gross conversion efficiency and protein turnover by an average of 16%. However, further exposure during the period of peak ambient temperatures, led to an average 20% reduction in growth, appetite, gross conversion efficiency and protein turnover. 3. 3. Increased rates of gill protein turnover and arguably lower rates of growth indicate that the cost of living for a trout acclimated and maintained in synthetic softwater is higher than that of hardwater fish. In addition, lower appetite in softwater fish suggest that life in softwater is itself a mild form of environmental stress.