Trimma okinawae

Trimma okinawae (Aoyagi, 1949)

Common Names

Bia (Tagalog), Okinawa pygmy-goby (English), Okinawa rubble goby (English), Okinawa-benihaze (Japanese), Orange-red goby (English), Red-spotted dwarfgoby (English), 冲绳磨塘鳢, 冲绳磨鰕虎, 沖繩磨塘鱧, 沖繩磨鰕虎

Languages: English

Overview

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)

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Ecology

Habitat

Trimma okinawae inhabits cave ceilings, rock slopes, holes, and the underside of table corals (Sunobe & Nakazono, 1990, 1993).

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Distribution

Trimma okinawae is distributed from Kagoshima Prefecture to the Ryukyu Islands, Japan (Sunobe & Nakazono, 1990, 1993).

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Reproduction

Sequential hermaphroditism (i.e., an individual changing its sex during its lifetime) is characteristic of the life histories of a number of fish species. In most species, sex change appears to occur only once in an individual’s lifetime, either from female to male (protogyny = “first female”) or male to female (protandry = “first male”). Much of this sex change variation seems to be explained by the "size-advantage model" (Warner, 1988). The essential idea behind this model is that if reproductive success increases with size or age more rapidly for one sex than it does for the other, an individual that changes sex in the appropriate direction during its lifetime will have a greater lifetime reproductive success than one that does not change sex. In polygynous mating systems, male reproductive success is often more strongly size-dependent than is female reproductive success because large males are able to monopolize mating opportunities at the expense of smaller males. Such a circumstance favors an individual reproducing as a female when small, then changing sex to male when it is larger. In contrast, in situations in which large males cannot monopolize mating opportunities (as is the case with monogamy or random mating), female reproductive success can be more strongly size-dependent than male reproductive success. This circumstance favors an individual reproducing as a male when small, then changing sex to female when it is larger.

Trimma okinawae belongs to a subset of sex-changing fish species in which bidirectional sex change has been documented. Such a life history pattern might be predicted if the relative value of being male versus female changes more than once during a lifetime. (Manabe et al. 2007, Journal of Fish Biology, and references therein). In this species, individuals typically live in polygynous groups and there is a size-based dominance hierarchy within a group. The largest individual in a group is the male, and the smaller individuals are females, with larger males tending to have larger harems (Sunobe & Nakazono, 1990, 1993;  Manabe et al. 2007 JFB).  After the disappearance 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.  In this species, the largest female in a group can benefit from changing sex to male because she can then monopolize matings with several females. A very different situation may apply when a dominant male changes social group and he comes into social contact with a larger male. In this case, his reproductive success might drop to zero since larger males monopolize mating opportunities to the detriment of smaller males. Consequently, the reproductive success of the smaller male is lower than that of females of the same size. In this situation, reproducing as a female is likely to increase the reproductive value of the smaller male, favoring the transition from male to female. Therefore, the size-advantage model can explain the selective advantage of the bidirectional sex change that has been documented in T. okinawae. (Manabe et al. 2007, Journal of Fish Biology)

During its breeding season (June to September in Kagoshima), the females produce a new clutch every 4 to 5 days (Sunobe & Nakazono, 1990, 1993).

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Associations

Trimma okinawae feeds on planktonic copepods (Sunobe & Nakazono, 1990, 1993).

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Taxonomy

  • Eviota caesiura okinawae Aoyagi, 1949 (synonym)

References

Manabe, H., Ishimura M., Shinomiya A., & Sunobe T. (2007).  Field evidence for bi-directional sex change in the polygynous gobiid fish Trimma okinawae. Journal of Field Biology. 70, 600-609.
Manabe, H., Ishimura M., Shinomiya A., & Sunobe T. (2007).  Inter-group movement of females of the polygynous gobiid fish Trimma okinawae in relation to timing of protogynous sex change. Journal of Ethology. 25, 133-137.
Sunobe, T., & Nakazono A. (1990).  Polygynous mating system of Trimma okinawae (Pisces: Gobiidae) at Kagoshima, Japan with a note on sex change. Ethology. 84, 133-143.
Sunobe, T., & Nakazono A. (1993).  Sex change in both directions by alteration of social dominance in Trimma okinawae (Pisces: Gobiidae). Ethology. 94, 339-345.