Aspects of the Energy Metabolism of Lake Sturgeon,Acipenser fulvescens, with Special Emphasis on Lipid and Ketone Body Metabolism

Abstract

Key enzymes in several metabolic pathways in five tissues were measured in a primitive osteichthyan, the lake sturgeon (Acipenser fulvescens). Levels of nonesterified fatty acids (NEFAs) were measured in the plasma as an indicator of fatty acid mobilization and differential utilization of individual NEFAs as substrates for lipid oxidation. The metabolism of lake sturgeon differs from that of most teleosts studied; it has detectable levels of beta-hydroxy-butyrate dehydrogenase in all tissues, possibly a primitive metabolic feature of vertebrates, subsequently lost in the teleosts. Based on HOAD and CPT activities lipid oxidation in extrahepatic tissues of sturgeon is intermediate between elasmobranch and teleost models. Sturgeon plasma NEFA concentrations are clearly higher than those detected in any elasmobranch, indicating that the acipenserid chondrosteans may be among the first jawed fish to mobilize and transport NEFAs. Oleic acid (18:1,n9) which amounts to 45% of total NEFA content of the plasma may be a preferred substrate of carnitine dependent oxidation. High levels of long chain fatty acid in the plasma may represent a high turnover of eicosanoid precursors. The low levels of LDH in the anoxia tolerant sturgeon may indicate that alternative anaerobic end products, perhaps ethanol, are used to survive under anoxic conditions.