Fishy Business

Henry C. Schultz III

This month, I cover an article on sex change in Centropyge ferrugata...

Yoichi Sakai, Kenji Karino, Tetsuo Kuwamura, Yasuhiro Nakashima and Yukiko Maruo. 2003. Sexually Dichromatic Protogynous Angelfish Centropyge ferrugata (Pomacanthidae) Males Can Change Back to Females. Zoological Science 20: 627-633.

Abstract:

Protogynous hermaphroditism, female-to-male sex change, is well known among reef fishes where large males monopolize harems of females. When the dominant male disappears from a harem, the largest female may change sex within a few weeks. Recently, from experiments with some protogynous haremic fishes in which two males' cohabitated, it was confirmed that sexual behavior and gonads were completely reversible according to individual social status. However, the ability to reverse secondary-developed sexual body coloration has never been examined in any protogynous fish. We conducted two male cohabitation experiments with the protogynous haremic angelfish, Centropyge ferrugata, which has conspicuous sexual dichromatism on the dorsal fin. Smaller males of C. ferrugata soon performed female-specific mating behaviors when they became subordinated after losing a contest. They then completed gonadal sex change to females 47 or 89 d (n=2) after beginning cohabitation. In the course of the reversed gonadal sex change, male-specific coloration on the dorsal fin changed to that of a female. Thus, the sex of C. ferrugata, including secondary developed sexually dichromatic characteristics, can be completely reversible in accord with their social status.

Comments:

In 1978 Moyer and Nakazono showed Centropyge interruptus to be a protogynous hermaphrodite. In its day this was an important discovery toward advancing our knowledge of marine angelfishes. Subsequently, Centropyge shepardi was shown also to be a protogynous hermaphrodite (Randall and Yasuda, 1979). All marine angelfish males are now believed to result from a female having undergone a female-to-male sex change.

The discovery of bi-directional sex change (Sakie et. al. 2003) is as important today as the Moyer and Nakazono discovery was in 1978. Considering the history of our knowledge of this genus, would it be fair to assume that all species of Centropyge are capable of bi-directional sex change? Only further research can definitively answer that question; however, some relevant observations may be gleaned from "experiments" conducted by astute aquarists. Our access to and willingness to keep multiple aquariums; our sometimes seemingly endless flow of "grants" that help fund our endeavors; and the passion with which we dedicate ourselves, and that makes hours of observation nothing short of a complete joy; all contribute to make serious hobbyists "observational researchers."

Be forewarned: the journey is not without risks. Eight male Centropyge ferrugata began the experiment, but only three survived and two reverted to females. The first pair's male was able to revert to female and produce eggs, which were fertilized by the male of the pair, 47 days after the start of the experiment. Additionally, the intense 400 - 500nm wavelength color pattern characteristic of the male C. ferrugata dorsal fin, which was present only two months before, was now absent. It is important to note that the male coloration was still present 32 days into the experiment, the day that nuzzling was first observed between the two subjects. Nuzzling is the third stage of Centropyge courtship. The second pair's male reverted from releasing sperm to having "considerably developed ovarian parts though it lacked vitellogenic oocytes or preovulated eggs in the gonad" after 89 days of cohabitation. Their conclusion was that the fish was "in the process of the gonadal sex change to become a functional female." It is important to note they ended the experiment themselves at roughly the same time the spawning season ended at Sesoko Island, the location where the males were first observed for six months, and where they were later captured for use in the experiment.

Such a series of observations can be attempted at home with any two Centropyge of the same species. Centropyge species exhibit sexual dichromatism and/or dimorphism along the rear edges of their soft dorsal fins, in the form of color changes, fin structure or both (Moyer, 1990). Documenting the sex-change process photographically from start to finish, especially concentrating on images of the dorsal fins, would be paramount to noting changes over the course of 30 to 90 days or more.

Following the research protocol used by Sakie et. al. (2003) would be the best course to follow. The article detailing the research should be read before starting, to ensure both similarity of research methods and comparability of results. Among other things, they used a 4' long aquarium divided in half by a 10mm mesh barrier. The barrier was fixed in place for 10 days to keep the territorial disputes non-destructive. The net was removed for 15 minutes on day 11, 20 minutes on day 12, and completely removed on day 13. The larger of the two fish attacked aggressively on day 11, but by day 12 the smaller of the two was displaying laterally in a show of conceding the battle. After this concession and the permanent removal of the mesh net the pair reportedly calmed and the male ceased its aggressive attacks. I expect that the smaller fish will become the female. If your chosen species of Centropyge is similar to C. ferrugata, you may begin to witness spawning courtship within the month and fertilized eggs within two months.

Addtional References:

Moyer, J.T. and A. Nakazono, 1978. Population structure, reproductive behavior, and protogynous hermaphroditism in the angelfish Centropyge interruptus at Miyake-jimi, Japan. Japan J. Ich

Moyer, J.T. 1981. Interspecific spawning of the pygmy angelfishes Centropyge shepardi and C. bispinosus at Guam. Micronesica 12(1-2): 119-124.

Moyer, J.T. 1990. Social and reproductive behavior of Chaetodontoplus mesoleucus (Pomacanthidae) at Bantayan Island, Phillipines, with notes on pomacanthid relationships. Jpn. J. Ichty. 25: 2-39.

Randall, J.E. & F. Yasuda. 1979. Centropyge shepardi, a new angelfish from the Mariana and Ogasawara Islands. Japan. J. Ichthyol. 26: 55-61.