Open Access

Dualistic reproductive behavior in the protogynous wrasseThalassoma bifasciatum and some observations on its day-night changeover

  • R. Reinboth1
Helgoländer wissenschaftliche Meeresuntersuchungen24:BF01609510


1.Thalassoma bifasciatum is a protogynous wrasse with (partial) sexual dimorphism and male dichromatism. Sex-inversion takes place without affecting the color pattern.

2. Males with female-like color dress indulge in group spawning; males with the bright color pattern perform pair spawning.

3. Among the brightly colored males exists a well-established hierarchy. Dominant males only have a particular spawning area in which they spawn daily at a certain time around noon. The spawning area is optically marked by conspicuous behavior of the bright male. Courtship activities towards individual partners are rather superficial.

4. The female has the leading role in pair spawning. In the extremely short spawning act a female may release, simultaneously, more than 2000 eggs.

5. Group spawning occurs in well-populated reef areas only. The basic pattern of group spawning has many similarities to pair spawning.

6. Day-night changeover ofT. bifasciatum is closely correlated to the time of sunset and sunrise.

7. The possible biological significance of the dualistic spawning behavior is discussed, and advantages as well as drawbacks of studies in the sea and in aquaria are considered.