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| Melanotaenia eachamensis [Lake Eacham] - photo© Gunther Schmida |
Allen and Cross, 1982
Lake Eacham Rainbowfish
Melanotaenia eachamensis were initially found only in Lake Eacham, a crater lake located on the Atherton Tablelands about 40 km south-west of Cairns in northern Queensland. The lake has a northeast-southwest length of around 1.5 km and 1 km wide. Water in the lake is supplied entirely from the catchment area within the crater rim. The water of the lake is neutral with a low level of dissolved salts, with water temperatures between 18-28° C. The lake is permanent and deep, and fluctuates seasonally with a maximum depth of 65.5 m during the wet season.
Melanotaenia eachamensis is a small rainbowfish species. They may reach a maximum size of 8 cm SL, but are usually less than 6 cm. They have a slender and compressed body with depth increasing with age. Males can be distinguished from females on the basis of differences in colouration and shape of the dorsal, anal and ventral fins. The original males collected from Lake Eacham had an overall bronze body colouration. The first dorsal fin was jet black while the second dorsal and anal fins had a maroon red colouration. Females were rather plain compared with the males and had smaller more rounded dorsal and anal fins.
Gerald Allen collected the Lake Eacham rainbowfish in 1978 and they were described as Melanotaenia eachamensis in 1982, although it was considered to be closely related to the widespread Melanotaenia splendida. Allen and Cross described the new species on the basis of differences in colour and body shape from surrounding populations of Melanotaenia splendida.
During "official" surveys of Lake Eacham in 1973 and 1974 the fish fauna consisted of only Melanotaenia eachamensis, Craterocephalus stercusmuscarum and Mogurnda adspersa. The rainbowfishes were abundant within the lake at that time, but during the 1980's, four native fish species (Amniataba percoides, Glossamia aprion, Nematalosa erebi and Toxotes chatareus) were translocated into the lake and it was noticed that the rainbowfish were no longer present.
Rainbowfish were first reported in Lake Eacham in 1965 by members of the Townsville Aquarium Society, but they were generally considered not to be as brightly coloured as other rainbowfishes from the coastal regions. They were never collected however, (well, not officially anyway), and there is no record of them having being maintained in the hobby in those early years. Allen and Cross's description of the Lake Eacham rainbowfish helped to stimulate interest in keeping the fish and fortunately a few specimens were collected for the aquarium hobby in 1982.
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| Melanotaenia eachamensis [Walkamin] - photo© Gunther Schmida |
In 1987, Barlow et al. surveyed the lake but failed to locate any rainbowfishes, though the four introduced species were plentiful, thus they were declared extinct in the wild (some remained in captivity). Following their reported extinction, in November 1989, three-thousand "Walkamin eachamensis" bred from captive stocks were released into Lake Eacham, but none could be located in surveys just three months later and throughout 1990.
In addition to the above translocations, Lates calcarifer were collected there in 1990-1991. Hephaestus fuliginosus and Melanotaenia splendida have also been translocated there and are still present. Ironically, Melanotaenia splendida are now present in large numbers and another species, believed to be an exotic has also been observed. All these fish species have been stocked into the lake unofficially, even though the lake is located in a National Park and part of the Wet Tropics World Heritage Area.
There are three volcanic lakes (Eacham, Barrine and Euramoo) that occur within close proximity of each other on the Atherton Tablelands. Lake Euramoo has a relatively small catchment area of about 4500 m² with no inflow or outflow channels. The lake has a water depth averaging around 20 metres in the northern end and 16 metres in the southern end, though there are seasonal fluctuations in water depth of between 2 and 3 metres. Lake Barrine is on average 67 metres deep. It is about 1 km in diameter, has a shoreline of almost 4.5 km and is the largest of the natural volcanic lakes in the area. The surrounding area of both Lake Eacham and Lake Barrine contain creeks that flow into Tinaroo Dam (Barron River) but are not associated with the lakes themselves. Both of these lakes are very close to the impoundment area of Tinaroo Dam into which Wright Creek and Congoo Creek flow. Lake Barrine has flood-flow connections to Toohey Creek, an upper tributary of the Mulgrave River.
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| Melanotaenia eachamensis [Dirran Creek] - photo© Gunther Schmida |
During 1988, other rainbowfishes of uncertain identity were found in Dirran Creek (North Johnstone River) and Lake Euramoo. Lake Barrine also contained rainbowfishes of uncertain identity, although these were listed as Melanotaenia splendida at the time. However, in a brief survey of Lake Barrine in 1991 numerous Glossamia aprion were found, but no rainbowfish. As Lake Barrine has a flood-flow connection to the upper Mulgrave River via Toohey Creek, the rainbowfish in Lake Barrine may have been the common Melanotaenia splendida or if the waterfalls in the upper Mulgrave and Toohey Creek prevented colonisation by Melanotaenia splendida, they may have been another form of rainbowfish. Rainbowfish from Lake Euramoo were analysed as part of the genetic studies of Lake Eacham rainbowfish during the 1990's (Zhu et al. 1998, McGuigan et al. 2000). However, no specimens from Lake Barrine were included in the study as the researchers could not locate any there. A number of predatory native fishes have also been translocated into Lake Barrine. Incidentally, translocated native predators are now found in Dirran Creek.
In 1983, I obtained wild-caught specimens of another rainbowfish of uncertain identity from Mobo Crater. Mobo Crater is located between Lake Euramoo and Lake Barrine. This fish was being distributed within the native fish hobby in Australia as Melanotaenia eachamensis (Mobo Crater) as late as 1999, but the original wild-caught fish looked nothing like the real Melanotaenia eachamensis. As far as I know no specimens from Mobo Crater were included in any of the above studies. This form however, now seems to have disappeared from the aquarium hobby?
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| Melanotaenia eachamensis [Lake Euramoo] - photo© Neil Armstrong |
Following on from there, Crowley and Ivantsoff (1991) conducted electrophoretic analyses of a number of the captive-bred Lake Eacham rainbows and reported that they could not distinguish electrophoretically between Melanotaenia eachamensis and Melanotaenia splendida. However, studies by Moritz et al. (1995) reported contrasting conclusions. DNA analyses of rainbow collections from catchments adjacent to Lake Eacham and captive bred specimens confirmed Melanotaenia eachamensis as a separate species distinguishable from Melanotaenia splendida from surrounding areas. Furthermore, rainbows from Lake Euramoo and Dirran Creek exhibited a 'pure' lineage with Melanotaenia eachamensis (Moritz et al., 1995).
Using an analysis of morphological and meristic characters, Pusey et al. (1997) believed Melanotaenia eachamensis to be even more widespread, occurring in many upland and several lowland tributaries and reaches of the North and South Johnstone Rivers; in upland tributaries of the Herbert River; upper Tully River and the upper Daintree River. Subsequent genetic work (Zhu et al. 1998, McGuigan 2000, McGuigan et al. 2000, Hurwood and Hughes 2001) suggested that at least some of these occurrences are not Melanotaenia eachamensis but either unusual variants of Melanotaenia splendida, Melanotaenia utcheensis or populations displaying alleles (one member of a pair or series of genes that occupy a specific position on a specific chromosome) of more than one species. Melanotaenia utcheensis were described as a new species in 2000, with populations known from Utchee, Fisher, Rankin and Short Creeks in the North and South Johnstone catchments (McGuigan 2000).
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| Melanotaenia sp. [Streets Creek, Kuranda] - photo© Neil Armstrong |
Zhu et al. (1998) also found populations that contained a mixture of alleles from Melanotaenia eachamensis and Melanotaenia splendida, in other locations such as an irrigation channel from Tinaroo Dam (Walkamin "eachamensis"), Streets Creek (Kuranda Reds), upper Barron, and other tributaries of the North and South Johnstone Rivers such as Williams Creek and Ithaca Creek. The finding of fish with Melanotaenia eachamensis alleles in irrigation channels of Tinaroo Dam would probably represent a translocation of these species to the upper Barron River catchment. The unusual distribution of Melanotaenia eachamensis alleles demonstrated by Zhu et al. (1998) may also suggest that it was translocated to other locations, and raises the possibility that even Lake Eacham may not have been their original habitat. It has been suggested that Melanotaenia utcheensis and Melanotaenia eachamensis were the original inhabitants of the region and Melanotaenia splendida may have invaded relatively recently. The species boundaries of all three species are not well defined and recent evidence suggests that at least some populations have hybridised in the streams of the Cairns-Atherton region.
In general, rainbowfishes evolve into different species and subspecies after becoming geographically isolated from others, adapting to their different environments, and changing over time through the process of natural selection. Geographic populations of Melanotaenia eachamensis have been isolated from each other for perhaps thousands of years. They have gradually evolved physical changes that reflect that adaptation. However, despite the research that has been undertaken to date, the specific status and distribution of Melanotaenia eachamensis still remains unclear.
Remarks
I obtained wild-caught specimens of Melanotaenia eachamensis in May 1982 and first spawned them in September of the same year. I maintained a small captive population until February 2000. However, in my opinion, these "genetic" look-alikes don't physically look like the original fish collected from Lake Eacham and maintained by myself for many years. While I would agree that the rainbowfish from Dirran Creek are very similar, the rest of the so-called "Melanotaenia eachamensis" look nothing like the original Lake Eacham fish.
I also have doubts about the validity of some of the "Melanotaenia eachamensis" being maintained in the Australian hobby today. The problem is that many of these "look-alikes" have and are being distributed and bred under the umbrella name "eachamensis" and present captive stocks do not look like the original fish. I suspect that there are very few (if any) genuine descendants of the original "Lake Eacham" rainbowfish still in existence. There may be some original stock in Europe and North America if they haven't been contaminated with the "look-alikes" as they have in the Australian hobby. Eggs were sent to North America and Europe in the 1980/1990's period where populations were established.
Whether or not these "look-alikes" are truly Melanotaenia eachamensis is a matter of on-going debate. Therefore, specific names based on the locality where each is found should be used by rainbowfish enthusiasts to identify each form. Where populations need to be identified, they should be sold and distributed by inclusion of a form or population identifier in brackets following the species name e.g. Melanotaenia eachamensis (Dirran Creek).
Literature
Allen, G.R. and Cross, N.J. (1982). Rainbowfishes of Australia and Papua New Guinea. Angus and Robertson, Sydney.
Allen, G.R. (1989). Lake Eacham rainbowfish rediscovered? Fishes of Sahul 5: 217-219.
Allen, G.R. (1995). Rainbowfishes: In Nature and in the Aquarium. Tetra-Verlag, Melle.
Barlow, C.G., Hogan, A.E. and Rogers, L.G. (1987). Implication of translocated fishes in the apparent extinction in the wild of the Lake Eacham rainbowfish, Melanotaenia eachamensis. Australian Journal of Marine and Freshwater Research 38: 897-902.
Burrows, D. W. (2004) Translocated Fishes in Streams of the Wet Tropics Region, North Queensland: Distribution and Potential Impact. Cooperative Research Centre for Tropical Rainforest Ecology and Management. Rainforest CRC, Cairns (83pp).
Crowley, L.E.L.M. and Ivantsoff, W. (1991). Genetic similarity among populations of rainbowfishes (Pisces: Melanotaeniidae) from Atherton Tableland, Northern Queensland. Ichthyological Exploration of Freshwaters 2, 129-137.
Hurwood, D.A. and Hughes, J.M. (2001). Historical interdrainage dispersal of eastern rainbowfish from the Atherton Tableland, north-eastern Australia. Journal of Fish Biology 58: 1125-1136.
McGuigan, K.L. (2000). An addition to the rainbowfish (Melanotaeniidae) fauna of north Queensland. Memoirs of the Queensland Museum 46: 647-655.
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: 713-723.
Moritz, C., Zhu, D. and Degnan, S. (1995). Evolutionary distinctiveness and conservation status of the Lake Eacham rainbowfish, Melanotaenia eachamensis. Final Report to Wet Tropics Management Authority, Department of Environment and Heritage. University of Queensland, St Lucia.
Pusey, B.J., Bird, J., Kennard, M.J. and Arthington, A.H. (1997). Distribution of the Lake Eacham rainbowfish in the Wet Tropics region, north Queensland. Australian Journal of Zoology 45: 75-84.
Pusey, B.J., Kennard, M.J. and Arthington, A.H. (2004). Freshwater Fishes of North-Eastern Australia. CSIRO Publishing, Victoria.
Russell, D.J. (1987). Aspects of the limnology of tropical lakes in Queensland - with notes on their suitability for recreational fisheries. Proceedings of the Royal Society of Queensland 98: 83-91.
Trenerry, M. and Werren, G. (1991). Fishes. Pages 104-107 In: Nix, H.A. and Switzer, M.A. (eds.). Rainforest Animals: Atlas of Vertebrates Endemic to Australia's Wet Tropics. Australian National Parks and Wildlife Service, Canberra. 112pp.
Zhu, D., Degnan, S. and Moritz, C. (1998). Evolutionary distinctiveness and status of the Lake Eacham rainbowfish (Melanotaenia eachamensis). Conservation Biology 12: 80-93.
© Copyright Adrian R. Tappin
Updated March, 2008.
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