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| Melanotaenia inornata [Flat Rock Creek] - photo© Günther Schmida |
(Castelnau, 1875)
Chequered Rainbowfish
Description
Melanotaenia s. inornata display a great natural assortment of colours. Populations of almost every river system have their own distinctive body colour and pattern. Consequently, specific names usually based on the locality where each is found are used by aquarium enthusiasts to identify each variety. Generally the body colour is olivaceous to yellowish with white breast. Scales on side of body with purplish sheen. Mid-lateral stripe deep yellowish anteriorly, and bluish-green or brownish-green on caudal peduncle. Other body stripes yellow or red. An orange or yellow spot on opercula. Dorsal, caudal and anal fins red and yellow chequered or orange-yellow with bright red spots on their membranes, with faint black edge. Not easily distinguished from Melanotaenia splendida splendida. Principal differences are body depth, fin counts, and colour pattern, which is variable depending on location and water conditions.
Distribution
They inhabit the river systems of the Northern Territory and Queensland, which flow into the Arafura Sea and Gulf of Carpentaria - from Darwin to Cape York Peninsula, extending down the east coast to around the Lockhart and Stewart Rivers. They are frequently found in company with Melanotaenia nigrans and Melanotaenia trifasciata.
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| Melanotaenia inornata [Moline Rockhole] - photo© Günther Schmida |
Habitat & Ecology
Melanotaenia s. inornata are tropical fish, and occur in almost every kind of freshwater habitat, from slow-moving streams, wetland swamps, lagoons and clear flowing rivers. They are generally found in waters with moderately thick vegetation. A temperature range of 23-40° Celsius (mean = 30.6°C); pH 4.6 to 8.3 (mean = 6.1); Conductivity 2 to 220 µS/cm and Dissolved Oxygen levels from 0.9 to 8.2 mg/L (mean = 5.8) on the surface, has been recorded in their natural environment. This wide range of water conditions matches the wide distribution of the species.
Melanotaenia s. inornata reach a maximum size of 15 cm, but usually less than 12 cm, with a body depth of 6-8 cm. they are sexually dimorphic, with males having longer and more brightly coloured fins, especially during the breeding season. Length at first maturity is estimated to be 25 mm for females and 33 mm for males.
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| Melanotaenia inornata [Darwin] - photo© Günther Schmida |
Melanotaenia s. inornata are reported to migrate upstream at the onset of the breeding season, which corresponds to the start of creek flow after the dry season. They appear to breed throughout the river system and lay a small number of relatively large eggs at a time; these are attached to aquatic vegetation by fine threads from the egg membrane. They spawn for an extended period during the early-wet seasons, and their gonads are developing for the next year's spawning by the late-wet-early-dry season. Juveniles are found throughout the year, which may suggest that this species spawns throughout the year. However, although juveniles are present throughout the year, this species mainly spawns at the onset of the wet season.
Under aquarium conditions, large females (> 50 mm TL) produce more than 100 eggs per day at the peak of their spawning. Smaller females (28-35 mm TL), which were only just sexually mature shed fewer eggs, 20-30 per day and do not spawn each day. Hatching occurs after 6-7 days. Two females were once observed to lay more than 1700 eggs within a single one-week spawning period. With a water temperature of 26°C Melanotaenia s. inornata can attain a total length of 20 mm in 86 days.
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| Melanotaenia inornata [Aligator River] - photo© Günther Schmida |
The main components of their diet are algae, aquatic insects, terrestrial insects and microcrustaceans. The algal component consists mainly of green filamentous species. A variety of aquatic insects are eaten; the main identifiable species being chironomid larvae and pupae, and coleopterans. The main terrestrial insects were formicids (ants) and the main microcrustaceans were cladocerans. Traces of hydrophytes, oligochaetes, gastropods, arachnids, macrocrustaceans, teleosts, terrestrial plants, detritus and inorganic material were also found in the stomachs. In the pools and riffles that enter the floodplain in the Wet season they feed mainly on non-aquatic insect forms such as winged diptera and ants. M. splendida inornata can therefore be classified as a meiophagous omnivore feeding opportunistically throughout the waterbodies.
Remarks
It should be noted that survival rates for Melanotaenia s. inornata sharply declined when the water temperature was raised. Such increases in temperature are common in waterbodies of northern Australia during the late dry season. Epizootic Ulcerative Syndrome or 'red spot' disease has been identified in Melanotaenia splendida inornata from a number of river systems in the Northern Territory. This condition is frequently fatal to juvenile fish. Mycobacteriosis is a disease of concern in captive populations of Melanotaenia splendida inornata. It causes a chronic wasting condition with continuous low, to moderate,
level mortality within the affected population, and can result in significant loss to fish culturists. The disease is considered
non-treatable once established in the fish host.
© Copyright Adrian R. Tappin
Updated January, 2007.
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