MEPS 155:173-188 (1997)  -  doi:10.3354/meps155173

Previous metabolic studies of scorpaenid fishes have measured inter- and intra-specific differences in physiological and biochemical capacities in fishes living at different depths. Small sample sizes and undocumented provenance of the samples studied have not allowed a full examination of the environmental basis for metabolic adaptation. The objective of this study was to determine the bathymetric demography of 22 scorpaenid fishes of the genera Sebastes and Sebastolobus, and to examine inter- and intra-specific changes in metabolic capacity in 4 of them (Sebastes goodei, Sebastes diploproa, Sebastolobus alascanus and Sebastolobus altivelis) representative of different environmental conditions. We attempted to collect samples that spanned the full depth and size ranges of each species. We examined changes in metabolic capacity as it was affected by size, depth of occurrence, and the existence of an oxygen minimum zone (OMZ) centered at 800 m. Lactate dehydrogenase (LDH) was measured as an indicator of glycolytic capacity. Citrate synthase (CS), a Krebs cycle enzyme, was measured as an indicator of aerobic capacity. Malate dehydrogenase (MDH), an enzyme which helps maintain redox balance between the mitochondrion and cytosol, was also used as an indicator of aerobic capacity. When normalized to a common size, S. goodei, S. diploproa, S. alascanus and S. altivelis displayed an inter-specific pattern of declining metabolic activity with depth of occurrence. Intra-specific size scaling of glycolytic capacity (LDH) was positive in the shallow-living S. goodei. However, no scaling occurred in S. diploproa and S. alascanus, and negative scaling of glycolytic activity occurred in the deep-living S. altivelis. MDH did not scale in S. goodei and S. diploproa but was negative in the 2 deeper-living Sebastolobus species. CS activity scaled negatively in S. goodei, S. alascanus, and S. altivelis, but the deep-water specialist, S. altivelis, had the steepest slope. S. altivelis was the only species where similar-sized individuals could be compared over a wide depth range. There was no elevation of LDH, or increase in anaerobic poise, in response to the hypoxia of the OMZ. Rather, all 3 enzyme activities were highest at 600 m and generally declined with increasing depth. Contrary to the existing paradigm, S. alascanus and S. altivelis were not found to be shallow- and deep-living congeners. Rather, S. altivelis is a permanent resident of deep water, while S. alascanus settles in shallow water then migrates to deep water with the onset of sexual maturity. When living in deep water, the supposed shallow water species, S. alascanus, maintains higher activities of all enzymes and grows an order of magnitude larger (>5000 vs <500 g). In deep-water slope habitats expected patterns of allometric scaling of white muscle enzyme activities appear to be altered by the limitations of food and oxygen availability, a pattern previously observed in flatfishes.

Metabolic adaptation · Deep-sea fishes · Oxygen minimum zone · Feeding rates · Lactate dehydrogenase · Citrate synthase · Malate dehydrogenase