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| Melanotaenia fluviatilis [Goldburn River] - photo© Günther Schmida |
(Castelnau, 1878)
Murray River Rainbowfish
Description
First described as Aristeus fluviatilis by Castelnau in 1878. They have been kept by aquarium hobbyists for many years and mistakenly referred to as Melanotaenia nigrans in aquarium literature. Until 1986 this species was considered the same as Melanotaenia duboulayi (both were known as Melanotaenia fluviatilis). Following a review of the rainbowfish group by Allen in 1980, they were renamed Melanotaenia splendida fluviatilis. However, a study of its early life-history stages by Crowley, et al., resulted in Melanotaenia splendida fluviatilis being separated into two species, Melanotaenia duboulayi from the eastern coastal drainage systems of northern New South Wales and southern Queensland, and Melanotaenia fluviatilis from the inland Murray-Darling River system.
Not easily distinguished from Melanotaenia duboulayi. Principal variations are body depth, fin counts, and colour pattern. In addition, there are clear differences in egg characteristics and larval development. Southern populations often have a broader head and blunter snout compared to fish from the northern part of the range. As with most rainbowfishes, the colour is variable depending on location and water conditions.
The basic colour is olive, brownish, or slightly turquoise on the back and upper side grading to white on the lower half. A thin reddish stripe is situated between each horizontal scale row, particularly in mature males. There is sometimes a blackish, mid-lateral stripe. Fins are clear to reddish, sometimes with faint spotting. Males may have blackish margins on the dorsal, anal, and anterior margin of the pelvic fins, especially during courtship and spawning. Prior to spawning the male's colour intensifies becoming emerald green, the throat orange and the tail fin red.
Distribution
This species occurs in the middle and lower sections of the Murray, Murrumbidgee and Macquarie Rivers, and in several other tributaries of the Darling River. Specimens collected from the Warrego, Paroo and upper Darling Rivers (and other streams between those tributaries) have been identified as Melanotaenia splendida tatei based on unpublished allozyme and mitochondrial DNA data. Melanotaenia fluviatilis are considered common and abundant in the Broken River and near Mildura in Victoria, around the Murray-Darling confluence, and in parts of the Goulburn River in Victoria. This species is also present in the middle to upper parts of the Gwydir River near Bingara, the Namoi River around the Peel River, Caroll Gap-Somerton on the Dumaresq River, and the Bogan River near Bogan Gate. It has also recently been recorded in low numbers near Gin Gin on the Macquarie River and Gongologon on the Bogan River. It is moderately common in some areas of its distribution range. However, Victorian and South Australian populations seem to be decreasing in number. This is not surprising, as the Murray River is the most used and abused river system in Australia.
This is the most southerly ranging rainbowfish in Australia and is the only species adapted to low winter temperature (normally around 10 to 15° Celsius). However, there is evidence that numbers are seriously reduced during winter periods, when water temperatures drop below 10° Celsius.
Habitat & Ecology
Occurs most frequently in relatively still, clear water, in water temperatures between 18-28° Celsius. Found in rivers, streams, billabongs, drainage ditches, reservoirs, overflows, swamps, and ponds with dense aquatic vegetation. Their natural environment is subjected to seasonal variations with water temperature, pH, and hardness levels varying considerably. They are usually found along grassy banks, or around sub-surface vegetation, submerged logs and branches.
A small species, slender and laterally compressed but depth increasing with age. Two dorsal fins, very close together, the first much smaller than the second. Mature males have a higher first dorsal fin, which overlaps the origin of the second dorsal fin when depressed. Females have smaller rounded dorsal and anal fins. May reach a maximum size of 10 cm, but usually less than 8 cm. Males are more brightly coloured, larger, and much deeper bodied than females.
Breeding takes place between October and January as water temperatures rise, with females producing between 100 and 150 eggs. Spawning occurs during the early morning or evening just before dark. Each female lays several eggs a day, which are summarily fertilised by the male. Eggs are held amongst the foliage of aquatic plants by several long, thin filaments originating at one point on the egg membrane. The water hardened eggs have a diameter of 1.3-1.8 mm, and hatch into larvae 2.5-3.1 mm in length 7 days after fertilisation at water temperatures between 25 and 29°C. Newly hatched larvae congregate near the water's surface within a few hours and begin feeding within 24 hours.
Melanotaenia fluviatilis is essentially carnivorous, feeding on both aquatic invertebrates associated with its weedy habitat and terrestrial arthropods which may fall onto or alight on the water's surface; however, it is also known to consume algae and fallen plant pollens.
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| Melanotaenia fluviatilis [Berry, South Australia] - photo© Günther Schmida |
Remarks
This species has never generated much interest among Australian aquarists, except for a few dedicated rainbowfish enthusiasts and is still relatively uncommon in the international hobby.
© Copyright Adrian R. Tappin
Updated January, 2007.
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