METABOLIC ORGANIZATION OF A PRIMITIVE FISH, THE BOWFIN (AMIA-CALVA)

Key enzymes in several metabolic pathways in five tissues were measured in primitive osteichthyan, the bowfin (Amia calva), the only living representative of the group of extant fishes most closely allied to the teleosts. Aspects of the metabolism of Amia differ from those of most teleosts studied. These differences include detectable levels of beta-hydroxybutyrate dehydrogenase in all tissues, possibly a primitive metabolic feature of vertebrates, subsequently lost in most more advanced teleosts. Based on 3-hydroxyacyl CoA dehydrogenase and carnitine palmitoyltransferase activities, lipid metabolism in extrahepatic tissues of bowfin more closely resembles that of an elasmobranch rather than that of a teleost. The overall level of metabolism is lower than most teleosts as indicated by enzyme activities in red muscle and heart. Bowfin plasma nonesterified fatty acid concentrations are lower than most teleosts, but higher than those detected in any elasmobranch. These data suggest that the metabolic organization, especially lipid and ketone body metabolism, at least in part, reflects the evolutionary history of this group.