Melanotaenia fluviatilis

Australian Rainbowfish

Classification

Melanotaeniidae

Distribution

Australia, specifically Queensland and New South Wales.

Habitat

It inhabits slow-moving parts of rivers and still waters such as ponds, ditches and lakes. Its habitats are usually characterised by clear water, thick with aquatic vegetation. Many of these habitats are subject to seasonal changes in terms of water temperature and chemistry, making this an adaptable species.

Maximum Standard Length

4″ (10cm), although females are usually smaller.

Aquarium SizeTop ↑

36″ x 12″ x 12″ (90cm x 30cm x 30cm) – 85 litres.

Maintenance

This species, like most rainbows, looks most at home in a planted aquarium. Provide areas of dense vegetation, along with some open areas for swimming. Other decor is not particularly important. The choice of plants should reflect the slightly hard, alkaline conditions preferred by the fish. Filtration and tank maintenance should be very efficient to encourage the male fish to develop their spectacular colouration.

Water Conditions

Temperature: 68-77°F (20-25°C), although it can withstand much lower (see below).

pH: 6.5-8.0. Aim for somewhere around neutral and you should be ok.

Hardness: 8-20°H

Diet

Unfussy and will accept most dried, frozen and live foods. Regular feedings of the latter will help to ensure the fish exhibit their best colours.

Behaviour and CompatibilityTop ↑

Very peaceful but can disturb smaller or slow-moving fish with its rapid movements and relatively large size. Good tankmates include other similarly-sized rainbowfish, characins, danios, barbs, and catfish such as Corydoras.
Like many other rainbowfish it can be quite skittish and does far better when kept in a shoal of at least 6-8, preferably more. The males will also be encouraged to display their best colours in the company of conspecifics. Obviously a suitably-sized aquarium would be required for a very large group.

Sexual Dimorphism

Males are larger and more colourful than females. As with other members of the genus, males also develop a characteristic high back as they mature.

Reproduction

As with other members of the genus, this is not a difficult species to breed, being an egg scatterer. The fry, however, can prove somewhat tricky to raise.

The breeding aquarium should be at least 30″ long, and contain slightly hard, alkaline water with a pH of around 7.5 and a temperature of 72-75°F. A small air-powered filter will provide sufficient oxygenation and flow. The tank should be filled with fine-leaved plants such as java moss, or nylon spawning mops. No substrate is necessary.

The adult fish are best conditioned as a group in a separate aquarium with plenty of live and frozen foods. As the fish come into condition, the females will appear noticeably plumper, and males will display to each other almost constantly. Males also intensify in colour, developing orange throats and red caudal fins. When ready, select the fattest, best-coloured pair and introduce them to the spawning tank. A small raise in temperature can often induce spawning. The pair will spawn for a period of several weeks, laying batches of eggs each day. These are attached to surfaces by a small thread. Although the adults tend not to eat the spawn, it’s easier to raise the fry in a separate aquarium. We recommend checking the plants or mops regularly and removing any eggs you find to a raising tank containing water from the spawning tank.

The eggs hatch in 6-10 days, depending on temperature and the tiny fry initially require infusoria–type food. They will graduate to free swimming foods, such as brine shrimp nauplii, after a week or so. Sinking foods are unsuitable, as the fry tend to stay very close to the water surface.

NotesTop ↑

Also known as the Murray River or crimson-spotted rainbowfish, this species is not as common in the hobby as some of its relatives, but can still be found from time to time. It is easily confused with the very similar M. duboulayi, indeed these two were once grouped together as a single species. However, there are clear differences in patterning, fin ray counts and the way in which their eggs and fry develop.

The range of M. fluviatilis extends further south than any other rainbowfish, and as such the fish can withstand relatively cool temperatures (often down to 50-60°F). This is because these parts of Australia cool down during the winter months. However, we would not recommend that it be subjected to extreme conditions such as these in aquaria, as it will be considerably less active and will lose colour. There is also evidence that the fish begin to die off below 50°F.