The rainbow fish of the Murray River, melanotaenia fluviatilis,it is one of many types of Australian rainbow fish. This group is primarily a group of tropical and subtropical fish, but the range of this fish extends into warm temperate areas and it is capable of withstanding fairly low water temperatures.
The Murray River rainbowfish is endemic to Australia. As its name suggests, it is located on the Murray River. It is also found in many, but not all, tributaries of the Murray and in various other river systems and lakes.
They can reach 4 inches (10 cm) in length, but most are smaller than this. Males tend to be larger than females.
Most of the articles on the internet about this fish suggest that a temperature between 22 and 26 degrees Celsius is ideal for this species. My experience suggests otherwise. Although it is a very versatile fish that will undoubtedly live healthy in an aquarium, being treated as if it were a tropical fish, the specimens with the best coloration are usually pond fish, subject to natural rises and falls in temperature with the different the seasons, as well as the different weather.
This fish is capable of taking on a wide range of conditions. Most places where it occurs naturally have a high pH and the water is quite hard. In an aquarium I suggest that the pH should be between 6.8 and 8. Excessively soft water is not ideal, but most tap water will have adequate hardness. As with all fish, chlorine or chloramine must be removed before it comes into contact with the fish.
This is an omnivorous fish. Like many of its relatives, it eats more plant material than most tropical fish. They will live on Tropical or Goldfish food, but this must be supplemented with plant matter. Duckweed (lemna species) is very easily eaten by this fish. They also like many kinds of vegetables. I cook vegetables hard enough to soften them. Zucchini is eaten just like cucumber, green peas and other vegetables. Like many fish, they also enjoy insect larvae such as mosquito larvae, small crustaceans such as daphnia, and small worms. Our River Murray Rainbow Fish gets frozen bloodworms once a week, as well as frozen brine shrimp once a week on a different day.