Contrasts in the capacity and underlying mechanisms for compensatory growth in two pelagic marine fishes

Abstract

The widespread capacity for teleost fishes to engage in compensatory growth suggests there are costs or trade-offs that constrain normal growth to sub-maximal rates. Some potential trade-offs include behavioral conflicts between foraging and avoiding predators, and physiological aspects of energy allocation between synthesis of new tissue and functional demands of metabolism and maintenance. We examined the capacity for compensation and some potential underlying mechanisms in juveniles of 2 northern Pacific fish species, walleye pollock Theragra chalcogramma and sablefish Anoplopoma fimbria. Fish were deprived of food for 2 to 3 wk, then returned to ad libitum rations. Growth rates were subsequently compared to those for continually fed fish for up to 16 wk, and potential trade-offs in behavior (food consumption, routine swimming speeds, and response to a predator) and physiology (indexed by critical swimming speeds) were examined during 3 time periods: immediately after deprivation, after 4 wk of ad libitum rations, and after 9 wk. We distinguished between routine swimming speeds, which indicate volitional motor activity, and critical swimming speeds, which estimate physiological capacity by forcing fish to swim to exhaustion against an increasing current. Previously deprived walleye pollock exhibited a clear, sustained capacity for accelerated growth, allowing them to quickly catch up in size to continually fed fish. Sablefish, however, exhibited only a minor level of growth compensation. Underlying mechanisms of compensatory growth also differed between the 2 species. Previously deprived walleye pollock increased food consumption to levels 3 to 4x greater than those of control fish and reduced energy expenditure by lowering routine swimming speeds. Compensating sablefish did not differ from control fish in consumption rates or routine swimming, but had lower critical swimming speeds than control fish, suggesting a trade-off in energy allocation. Responses to a simulated predator threat did not differ between previously deprived and continually fed fish of either species. The experimental results are suggestive of different mechanisms, behaviorally based for walleye pollock and physiologically based for sablefish, associated with accelerated growth. The differences between the 2 species in integrated processes of growth, behavior, and physiology are likely to be a function of their contrasting life history strategies and different baseline growth rates.