Comprehensive Description

Trimma okinawae is a small orange goby which reaches about 30 mm in length. It is distributed from Kagoshima Prefecture to the Ryukyu Islands, Japan, inhabiting cave ceilings, rock slopes, holes, and the underside of table corals, where it feeds on planktonic copepods. During its breeding season (June to September in Kagoshima), the females produce a new clutch every 4 to 5 days (Sunobe & Nakazono, 1990, 1993). These fish live mainly in polygynous groups and larger males tend to have larger harems (Sunobe & Nakazono, 1990; Manabe et al. 2007, Journal of Fish Biology). After the loss of a male, either the largest remaining female changes sex to male or a large female from another group immigrates and changes sex to male. Under some circumstances, males may become female as well, making T. okinawae one of a relatively small number of fish species known to undergo bidirectional sex change (see Reproduction, below). (Manabe et al. 2007, Journal of Fish Biology)