Abstract
In order to investigate diel patterns of vertical distribution and feeding of Japanese Spanish mackerel Scomberomorus niphonius larvae, day and night depth-discrete samplings were conducted in Hiuchi-nada, the central waters of the Seto Inland Sea, in June 1996 and 1997.
Japanese Spanish mackerel larvae exhibited a developmental stage related diel pattern of vertical distribution. Yolk-sac larvae did not show marked vertical movements, but diel vertical movement became evident after yolk absorption. During the day most larvae were caught in middle and bottom tows. In contrast a high percentages of larvae were captured in the upper-layer tows at night. Volumes of swim bladder of the larvae collected at night were larger than those in day, indicating larval dispersion upward by inflation of their swim bladder after dusk.
The diet of Japanese Spanish mackerel larvae consisted exclusively of other fish larvae. Clupeiformes fish were the dominant prey, followed by Gobiidae larvae. Percentage of stomachs with food and stomach fullness was high in day and peaked at dusk, then decreased throughout night. Stomach-contents of Japanese Spanish mackerel larvae became more diverse from dusk to midnight, primarily due to occurrence of Callionymidae and chub mackerel Scomber japonicus larvae which did not appear in stomachs during the day. Though primarily a daylight feeder, feeding at dusk may be very important since prey may be less active and more efficiently captured.
