Compensatory growth, energy storage and behavior of juvenile Pacific halibut Hippoglossus stenolepis following thermally induced growth reduction

For fishes settling over wide areas, spatial temperature variation can have a significant impact on growth rates during the early juvenile period. Size variation within cohorts and across years will depend on the thermal sensitivity of growth rate, the ability to move to favorable growth environments, and the potential to compensate for periods of reduced growth. We examined the growth, behavior and energy storage responses of juvenile Pacific halibut Hippoglossus stenolepis exposed to a thermally induced reduction in growth. Halibut reared for 12 wk at 2 degrees C then acclimated to and grown at 10 degrees C (delayed treatment) were compared to fish reared continuously at 10 degrees C (controls). Growth rates at 2 degrees C were 25% of those at 10 degrees C, resulting in a 2.4-fold difference in mass after 12 wk. Following acclimation to 10 degrees C, specific growth rates of delayed fish were 20% higher than controls. Complete compensation would have required 35 wk, assuming maintenance of observed growth rate differences between treatments. Rapid growth during the compensation phase was probably due in part to a reduction in the allocation of energy to lipid storage: length-corrected lipid levels of delayed fish were 14% lower than levels among control fish. Behavioral observations indicated that growth compensating fish were more active than control fish; this is assumed to reflect increased foraging activity. However, when presented with food, growth-compensating halibut did not initiate feeding more rapidly than control fish. The predation and starvation risks associated with increased activity and decreased energy storage appear to represent trade-offs with rapid compensatory growth in juvenile halibut.