Content of total and free amino acids in zooplanktonic food of fish larvae

The content of total and free amino acids in freshwater planktonic rotifers (Brachionus sp.), copepods (Eudiaptomus zachariasi) and groups of Daphnia pulex, Ceriodaphnia sp. and copepodites (Cyclops strenuus) of different sizes was determined. The amino acid content of Artemia salina nauplii on hatching and during fasting was also determined.

Amino acid content was lowest in rotifers and highest in stage III–IV copepodites. The major free amino acids in Cyclops strenuus dry matter were 1.43% arginine, 0.22% histidine, 0.20% alanine, 0.15% glutamic acid and 0.11% lysine. Free arginine content decreased in the daphnids as they increased in size. The content of all free amino acids in fasting Artemia nauplii was lower than in the freshwater zooplankters. The major free amino acids in nauplii were 0.55% proline, 0.41% alanine, 0.34% glycine and 0.37% serine. The content of most free amino acids in nauplii decreased during fasting. The significance of the results are discussed in relation to essential amino acid requirements of fish, and nutrition of fish larvae without fully developed gastrointestinal systems.