The Slender Rainbowfish was described by Allen in 1978 and its scientific name is Melanotaenia gracilis. The species was collected in 1975 by Hutchins, Curator of Fishes at the Western Australian Museum. Compared to most other Rainbowfish species, the adult male Slender Rainbowfish is noticeably slender and that is why its called “Slender Rainbowfish”. This fish is still comparatively unusual in the aquarium trade, especially outside Australia.   

Description
The Slender Rainbowfish can reach a length of 7 cm (almost 3 inches). It is olive coloured on the back and upper sides, while the lower part of the body has a pale purple shade. The body is divided by a distinct mid-lateral stripe. Sexing is easy, since the male fish has red margins on his dorsal and anal fins as well as red tips on the caudal-fin lobe.

Geographical distribution, habitat and conservation
The Slender Rainbowfish is only found in the Drysdale and King Edward River systems in Kimberly, a region located in the extreme northern part of Western Australia. The typical Slender Rainbow habitat is a rocky pool with clear water surrounded by eucalyptus, paperbark trees from the genus Melaleuca and palms from the genus Pandanus. The species is also quite common in large water courses, where the water flow decreases dramatically each dry season.

The species is still fairly abundant, but its natural range is very limited. It has been declared “Lower Risk: near threatened” by the IUCN Red List of Threatened Species.

Keeping Slender Rainbowfish in aquariums

Slender Rainbowfish Copyright www.jjphoto.dk

Try to mimic the natural environment for Melanotaenia gracilis when you decorate the aquarium. In the wild, large groups of Slender Rainbowfish congregate around submerged trees and you should therefore provide your fishes with similar sheltered spots in the aquarium, e.g. by including drift wood. Plants and rocks can also be used to create hiding spots. The recommended water temperature is 23-28 degrees C (73-82 degrees F). The water should be kept neutral or just a tad acidic, from pH 6.8 to 7.0. The Slender Rainbowfish is a peaceful species that can be kept in a species aquarium or together with other small and peaceful species in a community aquarium. Feed your Slender Rainbowfish algae based prepared food combined with meaty food, e.g. larvae and small crustaceans.  

Breeding Slender Rainbowfish
The Slender Rainbowfish is not difficult to spawn in the aquarium. If you keep your fish in a suitable environment and provide them with a varied and nutritious diet, they will often spawn without any additional coaxing. Water changes are very important. The Slender Rainbowfish will deposit its egg over bushy plants or spawning mops. Newly hatched Slender Rainbowfish fry can be fed infusoria until they are large enough to eat brine shrimp and powdered algae-based flake food.

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Other Australian Rainbowfishes

Cairns Rainbowfish
Threadfin Rainbowfish
Lake Eacham Rainbowfish
Exquisite Rainbowfish
Murray River Rainbowfish
Slender Rainbowfish
MacCulloch’s  Rainbowfish
Black-banded Rainbowfish
Pygmy Rainbowfish
Western Rainbowfish
Chequered Rainbowfish
Eastern Rainbowfish
Desert Rainbowfish
Banded Rainbowfish
Ornate Rainbowfish