Differences in gill raker morphology between two local populations of a benthophagous filter-feeding fish, Goniistius zonatus (Cheilodactylidae)

Gill raker morphology of a benthophagous fish Goniistius zonatus (Cheilodac tylidae) (10.9-29.2 cm SL), using a filter-feeding mode, was compared betwe en two locations (Morode and Arakashi) in southern Japan. Although gill rak er number and gill raker length at the two locations did not differ, gill r aker spacing was narrower relative to overall fish size at Morode than at A rakashi, mainly because gill raker width was greater at Morode. The differe nce of gill raker spacing is unlikely to have a genetic or physiochemical e xplanation. Small invertebrates (less than or equal to1.0mm) were dominant on the substrate at Morode but were less common at Arakashi. Such small ani mals were consumed by many fish at Morode but were rarely exploited at Arak ashi. At Morode, the narrow gill raker spacing would be effective in retain ing small prey, which should be an important energy resource in this popula tion. The difference of interraker spacing at the two locations seems to be related to available prey size at each location.