ブリ若魚に対するマアジ筋肉エキスの摂餌刺激効果

Abstract

The feeding-stimulatory effectiveness of a jack mackerel Trachurus japonicus white muscle extract and a synthetic mixture based on a reported analysis of an extract of the jack mackerel white muscle for young yellowtails Seriola quinqueradiata was examined by applying them in starch pellets. Pellets of the natural extract and the synthetic mixture were each offered to the yellowtails separately. The effectiveness of the two stimulants were examined by counting the number of pellets swallowed within the first one min after application of 100 pieces to a group of 20 fish.The pellets containing the natural extract were completely swallowed, while only 40% of those containing the synthetic mixture were eaten within the test period. The acceptability of both kinds of pellets markedly decreased at one tenth dilution. The effectiveness of the synthetic mixture showed a tendency to increase with increasing concentration, but attained only a 60% of that of the natural extract at a concentration five times that of the original.The stimulatory effectiveness for the palatine taste receptors of the two kinds of stimulants was also studied by recording the electrical response from the taste nerve. The natural extract was found to be more effective than the synthetic mixture over a wide concentration range tested. The threshold for the two was around -5 and -2 log unit dilution respectively.From both behavioral and electrophysiological examinations, the above findings suggest that an unknown substance (s) missing in the synthetic mixture may participate in the high stimulatory effectiveness of the natural extract.