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 (Cheilodactylidae) (10.9–29.2 cm SL), using a filter-feeding mode, was compared between two locations (Morode and Arakashi) in southern Japan. Although gill raker number and gill raker length at the two locations did not differ, gill raker spacing was narrower relative to overall fish size at Morode than at Arakashi, mainly because gill raker width was greater at Morode. The difference of gill raker spacing is unlikely to have a genetic or physiochemical explanation. Small invertebrates (≤1.0 mm) were dominant on the substrate at Morode but were less common at Arakashi. Such small animals were consumed by many fish at Morode but were rarely exploited at Arakashi. At Morode, the narrow gill raker spacing would be effective in retaining small prey, which should be an important energy resource in this population. The difference of interraker spacing at the two locations seems to be related to available prey size at each location.