Identification of feeding stimulants for greater amberjack Seriola dumerili in muscle tissue of jack mackerel Trachurus japonicus

Greater amberjack is a popular aquaculture species, but its nutritional requirements remain poorly understood. The present study aimed to identify feeding stimulants for greater amberjack from a synthetic extract (SE) of jack mackerel muscle. A bioassay involving a semi-purified casein diet supplemented with feeding stimulant candidates was performed. The SE was composed of amino acids, nucleotides, and other compounds. Relative feed intake (RFI) in the SE treatment was similar to that in the natural extract treatment. The all-nucleotide treatment [inosine monophosphate (IMP), inosine, adenosine monophosphate (AMP), adenosine diphosphate (ADP), and adenosine triphosphate (ATP)] showed a comparable RFI to that of the SE treatment. Furthermore, the RFI did not decrease when amino acids and other compounds were omitted from the SE, but significantly decreased when nucleotides were removed from the SE. Exclusion of inosine, AMP, ADP, and ATP had no effect on the RFI. Among nucleotides, only IMP supplementation showed a comparable RFI to that in the SE and all-nucleotide treatments. Even without IMP, RFI increased with increasing concentrations of nucleotides and their combined application (especially inosine + ADP). These results indicate that the feeding stimulatory effect of jack mackerel muscle extract on greater amberjack depended mainly on IMP.