Sudden degeneration of eyes just before settlement in the larva of Odontamblyopus lacepedii, the endemic goby to Ariake Bay, Japan

Abstract

The eel goby, Odontamblyopus lacepedii, with vestigial eyes, is endemic to Ariake Bay, Japan and is associated with shallow, muddy bottoms of estuaries. Larval distributions related to the metamorphosis of the species were examined around the upper estuary of the bay, which consists of a heavily turbid, vertically mixed, and strong tidal current. In the present study, we identified the larvae immediately after hatching. Their eyes were still enlarged with growth during the pelagic period but suddenly started to degenerate and became vestigial just before settlement during a 2-mm increment in body length. During this period, the larvae were vertically distributed from the surface and middle layer to the near-bottom and bottom layers with relatively high turbidity, and their pelvic fins rapidly developed; it is assumed that they changed their mode of life to be similar to that of adults. From these results, it is elucidated that the transition from a pelagic to a benthic lifestyle in this species synchronize with the eyes degenerate and buried under the skin, i.e., morphological and ecological changes occur in synchronization.