Like parrotfishes, many wrasses utilize some of the most complex and unusual reproduction systems known to fishes. Males can be either primary (born male), or secondary (females that have undergone sex change). In some species there are no secondary males while in others all individuals are born female (monandric) and change sex when necessary. In the most complex systems, species are diandric – both primary and secondary males exist in the population. In these species, individuals proceed through three distinct phases, marked by color differences. In fact, the color differences are so pronounced that for over 200 years researchers regarded some phases as distinct species. Sexually immature juveniles represent the first phase. The second, known as the initial, phase (IP) can include sexually mature males or females, which are impossible to tell apart without internal examination or observation during spawning. IP males and females may group spawn in some species. The terminal phase (TP) includes only mature males, which display brilliant colors. TP males usually dominate reproductive activity through a harem-based social system. The death of a TP male serves as a social cue for an IP female to change sex and behavior. The morphology of IP males may also change in response to the death of a TP male. In some cases, IP males attempt to fertilize IP females by following a TP male and IP female pair during spawning. In this behavior, called “streaking,” IP males follow the pairs at peak spawning and release a large cloud of gametes in an attempt to overwhelm fertilization by the TP male. This is thought to increase the fecundity (ability to produce offspring) of IP males. IP males are well equipped to perform streaking as they have larger gonads and so are able to produce more gametes, while TP males have smaller testes and rely on aggression to deter other males. The larger volume of milt (gametes) produced by IP males is related to group spawning events with IP females, in which competition for fertilization is intense and more milt is needed.
Some specific examples of wrasse mating systems demonstrate the complexity and variation of the phase system described above. For instance, the cleaner wrasse, which is monandric (all individuals are born female), forms harems that are held together by male aggression towards subordinate females. With the death of the dominant male, subordinate females jockey for position and the newly dominant female adopts aggressive male behavior within a few hours. Each individual moves a step up in the dominance hierarchy and the last position is filled by a juvenile. If the newly dominant female is able to withstand attempts by neighboring males to take over the vacant harem, she will become a fully functional male within a two to four days. Some other harem-forming species are Cirrhilabrus temminckii, Cirrhilabrus jordani, Labroides bicolor, Hemipteronotus splendens, Pseudocheilinus hexataenia and Macropharyngodon moyeri. The Caribbean species Halichoeres garnoti is also monandric, but individuals do not exhibit territoriality or conspicuous dominance relationships, nor do they use aggressive actions to maintain sexual state. Instead, size or some size-related factor determines which individual will fill the male role. In Halichoeres garnoti males are larger than females and both sexes behave similarly. While these examples focus on the mating extremes of wrasses, most species fall between the systems of the cleaner wrasse and Halichoeres garnoti in terms of the influence of social control on sex reversal. Other hermaphroditic but non-harem-forming species include Halichoeres bivittatus and Halichoeres poeyi, Halichoeres maculipinna and possibly Thalassoma lunare. Finally, some species, such as Oxyjulis californica and Crenilabrus melops, do not follow the phase system at all as they are not hermaphroditic, and there are probably more non-hermaphroditic species yet to be found.
Mating System: polygynous ; polygynandrous (promiscuous)
In tropical wrasses spawning occurs year-round but some temperate species seem to restrict spawning to warmer parts of the year. Spawning typically occurs along the outer edge of patch reefs or along the outer edges of more extensive reef complexes. The correlation between spawning and lunar periodicity (the lunar cycle) is sketchy in some species and non-existent in most that have been investigated. Spawning in several species corresponds with outgoing tides, however, many species spawn at a particular time in the day, regardless of tidal patterns. This variation may be due to local conditions. For instance, in areas where tidal forces are weak, factors like time of day or light intensity may have more influence. However, evidence from different species on the same reef suggests that temporal (measured time) differences in spawning evolved to decrease the probability of hybridization with other species.
Wrasses may spawn in groups or pairs depending on the species or phase of individuals. Typically, group or aggregate spawning occurs between initial phase (IP) individuals, which are diandric (containing male and female IP individuals). However, in some species, such as Thalassoma cupido, Thalassoma lucasanum, and Halichoeres bivitattus, terminal phase (TP) males have been observed participating in group spawning. The size of the spawning groups ranges from a dozen to several hundred individuals. Males outnumber females, sometimes by as much as ten to one. Paired spawning is found in many, if not all, tropical wrasses and involves a TP male and IP female. In rare cases, IP individuals also spawn in pairs. Most species defend small territories only during spawning. Currently Anampses cuvieri is the only known species of tropical wrasse to produce demersal eggs (eggs laid on the bottom as opposed to being released in the water column). Demersal spawning of Anampses cuvieri was only observed in captivity and still needs to be confirmed, but work on other species of this genus seems to support this observation.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sequential hermaphrodite (Protogynous ); sexual ; fertilization (External ); oviparous
Some temperate wrasse species, such as the ballan wrasse and Anampses cuvieri, are demersal nest builders. The nests are usually made out of plant material and the male guards the eggs after they are deposited.
Parental Investment: male parental care
- Thresher, R. 1984. Reproduction in Reef Fishes. Neptune City, NJ: T.F.H. Publications.
- Wheeler, A. 1985. The World Encyclopedia of Fishes - second edition. London: Macdonald.
- Choat, H., D. Bellwood. 1998. Wrasses & Parrotfishes. Pp. 209-213 in W Eschmeyer, J Paxton, eds. Encyclopedia of fishes – second edition. San Diego, CA: Academic Press.