Growth and behavioral responses to elevated temperatures by juvenile sablefish Anoplopoma fimbria and the interactive role of food availability

Larval and age-0 sablefish Anoplopoma fimbria reside in neustonic waters of the North Pacific during spring and summer. We estimated the potential impacts of elevated surface temperatures on ecological processes of growth, conversion efficiency, and behavior in early juvenile sablefish. Growth experiments tested a wide range of temperatures from 6 to 24 degree C, with fish receiving ad libitum or low (3% body weight d super(-1)) rations. With unlimited food, growth increased rapidly as temperature increased to 14 degree C, then displayed a more gradual rise to 22 degree C. Growth rates at the warmer temperatures were among the highest recorded for teleosts, attaining a maximum of 3.3 mm d super(-1) in length and a specific growth in weight of 11.8%. A similar response to temperature was observed at low rations, although at lower overall growth rates. At 24 degree C, there was a severe decline in growth for both ration levels, and few fish survived the 3 wk experiments. Gross growth efficiency, measured at temperatures of 6 to 22 degree C, displayed an interactive effect of temperature with ration level consistent with bioenergetic relationship. Conversion peaked at 16 to 20 degree C for fish receiving ad libitum rations, and at 10 degree C for fish on restricted rations. Conversion rates of sablefish were comparable to those calculated for a diverse array of fish species, suggesting that the rapid growth rates are driven by high consumption rather than unusually efficient energy transfer. Experiments analyzing sablefish behavior in thermally stratified water columns demonstrated increasing movement into colder water as ration level decreased, in agreement with an energy conserving strategy.