Hybridisation

Allen & Cross (1982) previously recorded only two hybrids between Chilatherina campsi and Melanotaenia affinis in their extensive examination of rainbowfish taxonomy covering all species known at that time. There have been some other reports of 'natural' rainbowfish hybrids being found in nature. However, hybridisation in nature is rare.

Zhu et al. (1994) and McGuigan et al. (2000) tentatively identified hybrids using mtDNA data for two Melanotaenia australis populations in the Northern Territory (Blackmore and South Alligator Rivers). Further evidence for hybridization was found in Lake Tinaroo between Melanotaenia eachamensis and Melanotaenia splendida (Zhu et al., 1998), and other populations were found containing a mix of mtDNA genotypes and morphologies (Pusey et al., 1997; Zhu et al., 1998; McGuigan, 2001). There is also some evidence that natural hybridisation has occurred between Melanotaenia splendida tatei / Melanotaenia fluviatilis; Melanotaenia duboulayi / Melanotaenia splendida splendida; Melanotaenia nigrans / Melanotaenia australis; Melanotaenia australis / Melanotaenia exquisita; and Melanotaenia exquisita / Melanotaenia splendida inornata. However, it remains unclear whether these mixes represent sympatry, ongoing hybridisation, or historical introgression.

The "Eachamensis" complex is north Queensland is really confusing, and even the "experts" cant seem to agree. One study reported that while Melanotaenia eachamensis and Melanotaenia splendida were shown to be genetically, meristically and morphologically distinct, many specimens in the study exhibited an intermediate set of characters suggesting that hybridisation between these species may be common place if intermediate body morphologies are indicative of hybrids. Further work on M. eachamensis and M. splendida has not been conclusive as far as I know. Maybe it is just a case of taxonomic or genetic confusion?

"Comet River" rainbowfish - photo© Gunther Schmida

Four rainbowfish populations were sampled from the Fitzroy River in Queensland. Two populations from the upper reaches of the Comet and Dawson river tributaries, and two populations from the lower portion of Fitzroy drainage from the upper Conner River and a lowland tributary of the Fitzroy River were sampled. Based on allozymes and mtDNA, the lower two populations were consistent with Melanotaenia splendida. The populations from the upper reaches were both consistent with Melanotaenia fluviatilis, with some Melanotaenia splendida alleles based on allozyme data, although they did have Melanotaenia duboulayi mtDNA. However this mtDNA type is common in Melanotaenia fluviatilis populations in the northern Murray-Darling catchment, the most likely source of these populations. Each of these populations represents extremes in terms of separation by river distance within this drainage. At some point(s) within this system both species likely came into contact. No information currently exists relative to where this contact is likely to be! ~ P.J. Unmack.

It has long been thought that streams straddling the Great Dividing Range, which extends down the east coast of Australia, have captured drainages on the opposite side. Captures of western flowing streams by those flowing east and vice versa have been variously debated over the last fifty years or more. For example, it has been suggested that the Barron and the Burdekin Rivers in northern Queensland captured previously western flowing streams. The Clarence River area of north-eastern New South Wales has also characteristics which suggest that drainage rearrangements may have occurred, although the precise nature and timing of these events is still uncertain. The Fitzroy/Dawson system is believed to have drained a coastal area spanning latitudes 20°S to 23°S. Presently, much of the coastal area near the mouth of the Fitzroy River is drained by short coastal streams, although the Fitzroy River drains a large inland area.

"Dawson River" rainbowfish - photo© Gunther Schmida

Rainfall in Australia is seasonal and also very variable, with floods in some years and drought in others. Ephemeral floodwaters allow dispersal of species and populations, both within and between river systems. Floodwaters from Queensland can end up in South Australia, covering a distance of 3000 kilometres. Although, for the most part, the different species of rainbowfishes can be distinguished from one another, there is the possibility that many species may only be examples of population variation within a single species.

There is much argument and discussion amongst biologists as to what a species actually is. The classic definition of a "species" is related organisms that share common characteristics and are capable of interbreeding. Some years ago a controlled breeding trial demonstrated that M. fluviatilis and M. duboulayi could interbreed and produce viable offspring. Therefore, both these species may just be different populations or varieties within a single species.

Because of this great variation in colours and body forms in many species of rainbowfishes, especially in Australia, all rainbowfishes should be bred within their own localised group. Regardless of their various colour patterns, they are capable and willing to breed together if permitted to do so. The serious hobbyist intent on maintaining pure lines must keep every variety in separate aquariums. Unless this is done, members of the different varieties will interbreed and complicate future breeding programs and identification. Also, females of many rainbowfish species are very similar and can easily be confused for one another.

I have kept rainbowfishes for more than 30 years and have always kept populations, even if they went by the same species name, separated for breeding. History has shown that this is the prudent thing to do. In the 1970s and 80s, many populations of rainbowfishes found their way into the aquarium hobby. As time went on and the various populations were more carefully studied, we learned that several of these populations were, in reality, separate species.

Many serious rainbowfish keepers will not bring new fish into their breeding program unless the breeder/collector has retained the location details. These hobbyists, for example, would not obtain a species with the name given only as Melanotaenia trifasciata, because the buyer does not know what he/she is getting. We may learn in the future that the different populations have some significant biological or genetic differences that may weaken the long-term viability and integrity of the species. Therefore, it is important to include a location name, such as Wonga Creek, Goyder River, etc. If the location name is lost, the fish should be distributed as an "aquarium strain".

Before being used for different rainbowfish species, spawning mops should always be boiled to destroy any eggs, which may still be attached to the mops. This procedure effectively precludes inadvertent hybridisation resulting from accidental carryover of eggs from the breeding set-up of one species to another, and demonstrates a significant advantage of using artificial spawning medium over live plants.

Most rainbowfish hybrids that hobbyists will come in contact with will just be unintended crossings. Although there are a number of 'commercial' hybrids available, they are usually sold and distributed under trade names such as 'Red Boesemani' etc. However, there are some unscrupulous people who are cross breeding rainbowfishes and selling them as true species. M. 'marcii', M. 'hammeri' and M. 'greetii' are such examples of commercial hybrids. These three hybrids were originally bred by a commercial aquarium dealer and breeder in the Netherlands. These hybrids, particularly 'marcii', often sold as the Marci Rainbowfish, have been widely distributed in Europe and North America. They are NOT valid species and should all be destroyed. However, on this point it's a matter for your own personal opinion.

Literature
Allen, G.R. and Cross, N.J. (1982) Rainbowfishes of Australia and Papua New Guinea, T.F.H. Publications, New Jersey.

Allen G. R. (1995). Rainbowfishes in Nature and in the Aquarium. (Tetra-Verlag: Germany.)

McGuigan, K.L., Zhu, D., Allen, G.R. and Moritz, C. (2000) Phylogenetic relationships and historical biogeography of melanotaeniid fishes in Australia and New Guinea. Marine and Freshwater Research 51(7): 713-723.

McGuigan, K.L. (2001) An addition to the rainbowfish (Melanotaeniidae) fauna of north Queensland. Memoirs of the Queensland Museum 46: 647-655.

Moritz, C., D. Zhu and S. Degnan. (1995) Evolutionary Distinctiveness and Conservation Status of the Lake Eacham Rainbowfish, Melanotaenia eachamensis. Final Report to the Wet Tropics Management Authority and Department of Environment and Heritage. University of Queensland, St Lucia, Queensland.

Pusey, B. J., J. Bird, M. J. Kennard and A.H. Arthington. (1997) Distribution of the Lake Eacham Rainbowfish in the Wet Tropics Region, North Queensland. Australian Journal of Zoology 45: 75-84.

Zhu, D., B.G.M. Jamieson, A. Hugall and C. Moritz (1994) Sequence evolution and phylogenetic signal in control-region and cytochrome b sequences of rainbowfishes (Melanotaeniidae) in Molecular Biology and Evolution 11: 672-683.

Zhu, D., S. Degnan and C. Moritz (1998) Evolutionary Distinctiveness and Status of the Endangered Lake Eacham Rainbowfish (Melanotaenia eachamensis). Conservation Biology 12 (1): 80-93.

© Copyright Adrian R. Tappin
Created July, 2003
Updated December, 2008