Studies on palatability of artificial feed for cultured fish.

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The feeding stimulatory effects of the extracts of organisms on the yellowtail, Seriola quinqueradiata, and ayu, Plecoglossus altivelis, were studied by offering the extractive substances in satarch or in a purified diet. The stimulatory effects on the taste and olfactory receptors were also studied.Yellowtail:(1) A synthetic mixture of extractive constituents of the mantle muscle of squid prepared based on reported analyses was eaten by the fish as equally as the natural extract of squid muscle when offered in starch. (2) Omission tests on the constituents of the synthetic mixture were performed dividing them into five groups. The results suggested that amino acids and nucleotides effective for the taste receptors might largely be responsible for the feeding stimulant activity of the squid extract. (3) The responses from the olfactory bulb on application of the above 5 groups of constituents to the olfactory epithelium did not consist with the results of the feeding experiments, showi … More ng the high sensitivity of the olfactory receptors to amino acids which were non feeding stimulatory. However, the response threshold of the olfctory receptors for the synthetic mixture appeared to be by 3 log units lower than that of the taste receptors. (4) The synthetic mixure for the jack mackerel muscle extract prepared based on reported analyses was less effective in feeding stimulation than the natural extract, suggesting that some potent substance(s) were missing in the mixture.Ayu fish:(1) The sensitivity of the taste receptors of the ayu fish to extractive substances was studied by recording the taste nerve responses. The taste receptors of this fish, like those of many other fishes reported, responded well to amino acids. Among the most effective at 10^<-2>M were Arg, His,phosphoserine,etc. The threshold for Arg and His was 10^<-6>-10^<-5>M.They also responded well to nucleotides such as AMP,CMP,etc. (2) Attached algae collected in the river were analysed. Compositions of ninhydrin reactive substances (NRS) in algae extract differed considerably with the extracting methods used. Among the most abundant amino acids were Ala,Glu,Gly,Val,etc.(3) Feed consumptions for 10 days in duplicate test groups of ayu fish were compared with control groups. As the results, 1) addition of freeze-dried algae to a purified diet showed the highest comsumption, 2) addition of water extract from algae showed about 70% effectiveness of that of the algae,and 3) amino acids mixture simulating NRS's composition of the algae extract showed only a weak effectiveness. Less