Bathymetric demography, enzyme activity patterns, and bioenergetics of deep-living scorpaenid fishes (genera Sebastes and Sebastolobus):paradigms revisited

Abstract

Previous metabolic studies of scorpaenid fishes have measured interand intra-specific diffcrt,nccs in physiological and biochemical capacities in fishes llving at different depths. Small sample sizes and undocumented provenance of the samplesstudied have not allowed a full examination of the environmental b a s t 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 intera l n t r a s p e c i f ~ c hanges in metabolic capacity in 4 of them (Sebastes goodei, Sebastes diploproa, Sebastolobrrs alascanus and Sel~astolobus altivelis) representative of different environmental conditions. Weattempted to collect samples that spanned the tull depth and size ranges of each species. We examined changes in mefabolic capacity as it was affected by size, depth ot occurrence, and the existence of an oxygen minimum zone (OMZ) centered at 800 m. Lactate dehydrogenasc (LDH) was measured as an indicator of glycolytic capacity. Citrate synthase (CS), a Krebs cycle enzyme, was measured as an indicator 01 aerobic capacity, Midate dehydrogenase (MDH), an enzyme which helps maintain redox balance between the mltochondrion and cytosol, was also used as an indicator of aerobic capacity. When normal17ed 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-livlng S. goodei. However, no scaling occurred in S diploproa and S. alascanus, and negative scaling of glycolytic activity occurred in the deep-living S. altivehs. 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-watc!r specialist, S. altivelis, had the steepest slope. S. altivehs was the only species where similar-sized individuals could be compared over a wide depth range. There was no elvvdtion 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 ~ncreaslng depth. Contrary to the existing paradigm, S. alascanus and S. altivelis were not found to be shallowand deep-living congeners. Rather. S. altivelis is a permanent resident of deep water, whlle 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 hlgher 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.