Lactate Metabolism in Fish

The activity of lactate dehydrogenase was measured in the livers of 36 species of fish. These species could be divided into two groups, those with liver activities of more than 1000 mU/mg protein and those with activities of less than 100 mU/ mg protein. The lactate and pyruvate of samples of blood, muscle and liver from cod, plaice, bass and mackerel were determined. Samples were taken from ‘rested’ and trawled fish and from fish allowed to recover for 3 h after trawling. The rate of removal of lactate from the white muscle after capture in the trawl was not related to high blood and liver activities of lactate dehydrogenase. There was no relationship between the activities of nine of the glycolytic enzymes in the white muscle of cod and plaice and the liver lactate dehydrogenase activity. Little blood lactate appears to be taken up by the liver. It is concluded that the liver of cod, plaice and bass has a negligible role in metabolizing blood lactate.