Melanotaenia tatei

Melanotaenia splendida tatei [Finke River] - photo© Gunther Schmida

(Zietz, 1896)
Desert Rainbowfish

Species Summary
Melanotaenia splendida subsp. tatei was originally named Nematocentris tatei by Zietz in 1896. This species was named in honour of Ralph Tate (1840-1901), a geologist and botanist who was on the 1894 Horn Expedition when this species was first collected.

During 1894 several colonial governments and museums collaborated to mount a major scientific expedition to the MacDonnell Ranges in central Australia. The expedition was named after its major benefactor, wealthy South Australian pastoralist and miner, W.A. Horn. With seven scientists, the expedition undertook the most intense scientific examination of central Australia to that date. Five fish specimens were collected during that expedition: Nematalosa erebi, Mogurnda larapintae (Finke River) Neosilurus hyrtlii (Cooper Creek), Chlamydogobius eremius (Coward Springs) and Melanotaenia splendida subsp. tatei. Chlamydogobius eremius was first described from specimens collected on the Horn expedition. Several new species of Chlamydogobius from inland Australia were described in the mid-1990s. Mogurnda larapintae was originally described from specimens collected on the Horn Expedition as well, but only recently accepted as a distinct species. Ongoing work on the genus Mogurnda by South Australian Museum researchers, using genetic techniques, has recently shown that more unrecognised species exist.

Melanotaenia splendida tatei [Spawning Colour] - photo© Neil Armstrong

The different subspecies of Melanotaenia splendida are not easily identified in relation to each other as they display a great variation of colours and markings. Principal visual differences are body depth and colour pattern, which is variable depending on location and natural environment. At the same time, body form within each subspecies is variably and appears to be related to habitat conditions, which can sometimes make correct identification difficult. Populations of almost every river system they occupy have their own distinctive body colour and pattern. Geographic distribution is very helpful; if you know where they were collected you can generally make a confident identification. Consequently, specific names usually based on the locality where each is found are used by rainbowfish enthusiasts to identify each variety. Where populations need to be identified, they are often done by inclusion of a form or population identifier in brackets following the species name e.g. Melanotaenia splendida (Burdekin River).

Whether or not M. s. tatei are truly a distinct subspecies is a matter of on-going debate. Ever since Carolus Linnaeus founded the modern system of classifying species in the mid-l8th century, taxonomists have argued over just what exactly species and subspecies are. In general, fishes 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 splendida have been isolated from each other for perhaps thousands of years. They have gradually evolved physical adaptations that reflect their habitat. Some biologists classify M. s. splendida as a separate subspecies because they are visibly different. Others say they are genetically the same as other Melanotaenia splendida subspecies and differ only because of environmental circumstances. How the evolution of the splendida group's systematics will be in the future, remains a question mark.

M. s. tatei is a small, laterally compressed fish. They may reach a maximum size of 10 cm, but usually less than 8 cm SL. The eyes are large and positioned towards the top of the head, and the mouth is moderately large, oblique and upturned. There are two dorsal fins separated by a small gap, with the first short-based and the second long-based. There is a long-based anal fin and the tail is moderately forked. Two colour forms exist; in one form males have a purple body with yellow-green fins, with dark flecks and a dark border. The other form has a blue-green body with similar colouration on their fins. During spawning the belly of the male turns bright pink. Colour varies depending upon the mood of the fish, water conditions and diet. Females and juveniles have plain silvery bodies with clear fins. Males are usually more brightly coloured with pale stripes along the sides, larger, and much deeper bodied than females.

Cooper Creek [Dry Season Habitat] - photo© Allan Travers

Distribution & Habitat
M. s. tatei is widespread and abundant in the larger rivers of the Lake Eyre Basin and the Western Plateau of the Northern Territory. This species has only recently been identified from the Murray-Darling Basin, where it is recorded from the arid rivers in the north-western basin. It is found only in the Paroo and Warrego rivers, and hybrids with Murray-Darling rainbowfish have been identified in the lowermost Warrego River and the Darling River from around the Bogan River down to at least Menindee. Any rainbowfish captured in or near the Darling River need to be carefully examined, as confusion or hybridisation with Murray-Darling rainbowfish is likely.

They inhabit semi-permanent streams, springs, artesian bores (wells), and lagoons. During prolonged droughts the fish are confined to isolated pools. Their natural environment is subjected to seasonal variations with water temperatures ranging between 24° Celsius during the dry season and up to 33° Celsius in the wet season. The water is generally alkaline (pH 7.2~8.0); however, they are occasionally found in acidic conditions (pH 6.5~6.9). They are usually found around sub-surface vegetation, submerged logs, or branches.

Biology & Ecology
Little is known of their biology, but they have broad physiological tolerances. Strong sexual dimorphism is present in the species with males typically being larger and brighter in colouration. During spawning the ventral region of the male turns bright pink. Spawning typically takes place during the warmer months when temperatures are above 20°C, or whenever ample rain falls. Females produce between 100 and 200 small eggs (0.8~0.95 mm diameter), spawning a number of times daily for several days. Eggs adhere to water plants and hatching occurs after 6~7 days. The newly hatched larvae are around 4~5 mm long. Spawning more commonly occurs in the morning with eggs being scattered over vegetation or aquatic debris. They probably mature within a few months at around 30~50 mm. They are omnivorous and will consume algae, aquatic plants and various invertebrates.

Literature
Duguid, A., Barnetson, J., Clifford, B., Pavey, C., Albrecht, D., Risler, J. and McNellie, M. (2002). Wetlands in the arid Northern Territory. A report to Environment Australia on the inventory and significance of wetlands in the arid NT. Parks and Wildlife Commission of the Northern Territory.

Unmack, P. J. (1995). Desert fishes down under. Proceedings of the Desert Fishes Council 1994, 26: 71-95.

Unmack, P. J. (2001). Biogeography of Australian freshwater fishes, Journal of Biogeography, 28, 1053-1089.

Wager, R. & Unmack, P. J. (2000). Fishes of the Lake Eyre Catchment of Central Australia. Queensland Department of Primary Industries, Brisbane. 90pp.

Zietz, A. H. C. (1896). Pisces. Report on the work of the Horn Expedition to Central Australia. Part 2. Zoology. Horn Expedition: 176-180, Appendix, pp. 410-411, Pl. 16.