Aquarists often dream of the perfect fish - beautiful colours, disease resistant, fast growing, and easy to maintain in an aquarium. Hybridisation could make this dream come true. However, consider what could happen, though, if this dream fish got out of the aquarium and into the real world. Would it mix with native wild fish and create new hybrids, or would it die out because it couldn't compete in the natural environment? Hybridised fish can be very similar to wild fish and may survive, reproduce and influence natural selection.
There have been some reports of 'natural' rainbowfish hybrids being found in nature. Gerald Allen has found a couple of hybrids in the wild and several others have caught an occasionally hybrid. However, most of these natural hybrids are rare. There is some evidence that hybridisation between Melanotaenia splendida tatei / Melanotaenia fluviatilis, Melanotaenia duboulayi / Melanotaenia splendida splendida, Melanotaenia nigrans / Melanotaenia australis, and Melanotaenia exquisita / Melanotaenia splendida inornata have occurred.
The 'Eachamensis' complex is north Queensland is really confusing, and even the 'experts' cant seem to agree. There was an earlier suggestion following genetic research of hybridisation between Melanotaenia eachamensis / Melanotaenia splendida splendida, and Melanotaenia splendida australis / Melanotaenia exquisita.
One study reported that while Melanotaenia eachamensis and Melanotaenia s. 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. s. splendida has not been conclusive as far as I know, although more work is continuing on this issue. Maybe it is just a case of taxonomic confusion?
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 Melanotaenia fluviatilis and Melanotaenia 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, breeding 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'. However, there are some unscrupulous people who are cross breeding rainbowfishes and selling them as true species.
Melanotaenia marcii, Melanotaenia hammeri, and Melanotaenia 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 of personal opinion.
© Copyright Adrian R. Tappin
Created July, 2003.
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