Fish metabolism under adverse conditions

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Research will address the impact of environmental challenges, especially low oxygen and temperature extremes, on the physiology and biochemistry of fish. The comparative / environment approach will be used in selecting animals that exhibit naturally occurring differences in blood glucose levels and resistance to freezing. 1) Glucose metabolism in hypoglycaemic and hypoxic fish. Extracellular glucose levels show considerable species variability. For instance, levels in sculpin, cunner, and Atlantic cod are typically about 0.5, 2.5 and 5 mM, respectively. Experiments will assess if extracellular glucose concentration is a primary determinant of glucose utilization but if glucose utilization is similar across species, just how this is achieved. Rates of glucose use will be determined and related to the amino acid sequences of membrane transporter proteins. Glucose transport mechanisms will also be studied in highly hypoxic resistant fish living in the high temperature Amazon River. The combination of low oxygen and high temperature places extreme demands on these species that may require novel biochemical strategies. 2) Glycerol uptake by rainbow smelt. Rainbow smelt is a small fish that feeds under the sea ice during winter. Freeze resistance is achieved to a large extent by the accumulation of high levels of glycerol (>200 mM). The chemical glycerol is similar to what is placed in car radiators in the winter. Glycerol accumulates in all tissues including red blood cells (RBCs). Unlike other tissues, RBCs are mobile, and during transit through the gills, should lose glycerol to the sea water. We believe that RBCs get recharged upon passage through the liver and that the uptake is dependent upon proteins known as aquaglyceroporins (AQGPs). The possibility that smelt RBCs have novel and unique AQGPs will be assessed. These experiments will reveal fundamental insights into metabolism that extend beyond the model systems. For instance, we may find that in species with low extracellular glucose, that the transporters have a higher affinity for glucose or that smelt RBCs have a previously uncharacterized AQGPs. These would be novel findings of biochemical adaptations to the environment.