Identification of Feeding Stimulant in the Krill Extract for Jack Mackerel

Abstract

In order to obtain further information on the feeding stimulant for the jack mackerel Trachurus japonicus, a series of feeding test were conducted using the purified casein basal diets flavored with the synthetic extract containing major groups stimulating those of a krill extract. The feeding stimulant activity of test compounds was evaluated by a bioassay method.
The complete synthetic extract of krill possessed a remarkable feeding stimulant activity, although the activity was lower than that of the synthetic extract of jack mackerel reported pre-viously. Subdivision of the synthetic extract showed that the group of amino acids plus nucleotides was highly active, while the individual amino acids, nucleotides and other bases groups as well as the groups of amino acids plus other bases and nucleotides plus other bases were inherently in-active. Therefore, the feeding stimulant activity of synthetic extract of krill for the jack mackerel was considered to be due to the synergistic effect of amino acids plus nucleotides. Among 20 amino acids examined at a concentration of 5mmol/100g dry diet, only L-tryptophan was found to possess a feeding stimulant activity for the jack mackerel.