Studies on stimulation of feeding behavior in yellowtail Seriola quinqueradiata

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The feeding-stimulatory effectiveness of a water extract of the jack mackerel Trachurus japonicus white muscle for the young yellowtail Seriola quinqueradiata was studied with the aid of gel chromatography, ion exchange chromatography and other analytical methods. The feeding-stimulatory effectiveness of test fractions of the extract was evaluated by applying them to the young yellowtail in starch pellets and counting the number of pellets eaten by the fish. (1) Gel fractions of the extracts on a column of Sephadex-15 The water extract of the muscle was ultrafiltrated through a filter membrane (UK-15, Advantic, M.W. cut off 10,000) and the ultrafiltrate was fractionated on a column of Sephadex G-15 from 0.05 M sodium chloride. The fractions obtained were divided into groups and pooled. Then the pooled eluate was freeze-dried and the residues were dissolved in sea water and applied to the fish. The results showed that effective compounds were included in fractions of molecular weight of several hundreds or lower. (2) Fractions of the extracts obtained by treating with DEAE-Sephadex and CM-Sephadex The ultrafiltrate of the muscle extract was treated with (a) DEAE-Sephadex A-25 anion exchanger, (b) CM-Sephadex C-25 cation exchanger or (c) both of the two ion exchangers in batch procedures. The results obtained showed that (a) reduced the stimulatory effectiveness of the extract. This suggests that some of the effective constituents are adsorbed to the DEAE-Sephadex;(b) had no apparent influence on the effectiveness of the extract; (c) resulted in a sever depression of the effectiveness, suggesting that constituents adsorbing to the cation exchanger also show a feeding- stimulatory effect in cooperation with constituents in the (c)-treated extract.