Bering Sea | Fishes and Fish Habitats
Determination of thiaminase activity in Alaska forage fishes Presenter: Drew Porter , dporter13@alaska.edu, University of Alaska Fairbanks Kathrine Howard , kathrine.howard@adfg.gov, Alaska Department of Fish and Game Cody Pinger , cody.pinger@noaa.gov, NOAA Alaska Fisheries Science Center
In recent years, western Alaska Chinook salmon ( Oncorhynchus tshawytscha ) have undergone population declines and reduced productivity, which has led to closures of subsistence, commercial, and sport fisheries. Early life stage mortality caused by a deficiency of thiamine (vitamin B1) is hypothesized to be a driver of these issues. Thiamine is an enzyme cofactor essential for cell metabolism that must be obtained through diet. Thiamine deficiency in salmonids from the Laurentian Great Lakes, as well as California’s Central Valley, has been attributed to consumption of fish prey containing thiaminase, an enzyme that destroys thiamine. Though thiamine deficiency has been observed in western Alaska Chinook salmon, the cause is unknown. Accordingly, we applied a rapid spectrophotometric assay to assess total body thiaminase activity (measured as nanomoles of thiamine degraded per gram per minute [nmol T∙g-1∙m-1]) in purported forage fish prey of western Alaska Chinook salmon. Samples were collected in 2021 and 2022 from the Bering Sea and southeast Alaska. Thiaminase activity varied among and within species by location. Activity was greatest in rainbow smelt ( Osmerus mordax dentax ; n = 16) with a mean value of 37.3 ± 38.4 nmol T∙g-1∙m-1. Notably, Capelin ( Mallotus villosus ) from southeast Alaska (n = 13) had mean thiaminase activity levels of 23.0 ± 18.9 nmol T∙g-1∙m-1, while individuals from the Bering Sea (n = 8) had much lower activity levels of 1.2 ± 0.4 nmol T∙g-1∙m-1 , with 63% of individuals not exhibiting any detectable thiaminase activity. Further, 78% of Pacific sand lance ( Ammodytes hexapterus ) from both regions (n = 23) contained no detectable thiaminase activity, with remaining individuals displaying a mean thiaminase activity level of only 1.0 ± 0.5 nmol T∙g-1∙m-1. Our study will also include saffron cod ( Eleginus gracilis ), walleye pollock ( Gadus chalcogrammus ), Pacific cod ( Gadus macrocephalus ), Pacific herring ( Clupea pallasi ), three-spined stickleback ( Gasterosteus aculeatus ), longhead dab ( Limanda proboscidea ), and squid ( Gonatus sp. ). Individuals will also be analyzed for thiamine and lipid content to further investigate the quality of Chinook salmon prey. The determination of thiaminase activity levels in forage fishes from Alaska will further the understanding of a potential driver of thiamine deficiency in ecologically and culturally important western Alaska Chinook salmon populations.
Alaska Marine Science Symposium 2023 209
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