A comparison of the nutritional condition of herring larvae as determined by two biochemical methods - tryptic enzyme activity and RNA/DNA ratio measurements

Abstract

Two biochemical methods for measuring larval fish condition – tryptic enzyme activity and RNA/DNA ratio measurement - were applied to laboratory-reared and wild-caught herring larvae. The comparison of both methods when applied to laboratory-reared herring larvae showed that tryptic enzyme activity and RNA/DNA ratio are linear and positively correlated under constant nutritional conditions. Wild-caught larvae were transferred to the laboratory and used to compare both indicators in relation to shortterm changes in food availability and long-term starvation periods (13 days). In the starvation experiments with the wild-caught larvae the lowest trypsin values were obtained after 3–4 days and a significant decrease in RNA/DNA ratios was obtained after 5–6 days. Prolongation of the starvation time did not result in a further significant change in either parameter. The results of the study demonstrate the usefulness of both methods in monitoring nutritional condition offish larvae in field samples.