Melanotaenia boesemani - Boeseman's Rainbowfish

Rainbowfish Problems? – Read This

Recently I heard some disturbing rumours flowing from Canberra, suggesting that Rainbowfish are too hard to keep because they are always sick with ulcers and die easily. However, I believe the answer to these problems is simple and in the following few paragraphs, I will put forward some ideas based on collecting and observing the wild fish and on conversations with rainbowfish enthusiasts in Brisbane and Melbourne.

Rainbowfish in the wild are foragers: they feed on Algae, higher plants, small crustaceans, aquatic insects, terrestrial insects, tadpoles and the occasional small fish. Algae are the one item of food that appears to be consumed the most. When a rainbowfish is taken from its creek, river, billabong or lake, the first thing to he noticed is that it excretes a long, dark green string of fibrous faeces. The fish has usually a streamlined shape and I think they get that way from having to work so hard to survive in their hostile environment.

Tropical areas have two main seasons; a wet and a dry. During the wet season, food is plentiful and this is when most reproduction occurs. The proteinaceous foods (crustaceans, insects, tadpoles, fish) are abundant. However, rainbowfish collected during the wet season still excrete the green fibrous faeces, after capture. When put into a well planted tank, the first thing they do (especially the larger ones) is consume your plants. Thus the inevitable conclusion is:-

Rainbowfish diet contains a large proportion of vegetable matter.

What happens if we feed a rainbowfish on an all-meat diet? I don’t know exactly but I have heard from a person who keeps beautiful and well proportioned rainbowfish in Queensland, that experiments are being conducted in relation to their diets. Rainbowfish that have been fed high protein diets are being dissected and they prove to have deposits of fat around their internal organs. Any animal that has too much fat in its system is stressed and the first lesson that we learn as aquarists is that stressed fish are more likely to be affected by disease organisms, which are present in all aquariums.

I therefore believe that the answer to poorly proportioned rainbowfish, ulcer disease and most of their other problems is in their diet, as well as in good clean water and uncrowded conditions.

Glossolepis incisus - Rode Regenboogvis
Glossolepis incisus – Rode Regenboogvis


If you don’t wish to take my word but are having troubles with deformed or diseased rainbowfish, then try the following experiment, which is easy to conduct. Take two equal-sized aquariums, set them up in exactly the same way and breed your favourite rainbowfish, keeping the same number of fry in each tank. Label one tank ‘Vegetarian’ and the other ‘Normal’ and keep a notebook to record differences between them. Feed the fish in the vegetarian tank with vegetarian flake food and frozen food mixture containing at least 50% vegetable matter but provide those in the normal tank with whatever foods you would normally use to obtain maximum growth. The growth rates in the two aquariums may well be different: in the vegetarian tank the fish may develop more slowly.

A suggestion for a frozen food containing plenty of vegetable matter would be cooked zucchini, boiled spinach or peas, or cooked pumpkin for one half of the mixture, the other half being prawns, cooked or frozen, and fish fillets. Stay away from beef heart and other land-animal products.

Insects form another important food for rainbowfish and freeze-dried or frozen mosquito larvae are usually available from the aquarium shop. Fruitflies are easy to culture and form a good alternative live food. Starter cultures of vestigial-wing fruitflies are available from Southern Biological Supplies in Melbourne and a recipe for a suitable culture medium is given in the book ‘Australian Native Fishes for Aquariums’, which should be in our library.

Rainbowfish will eat almost anything put in front of them, so it is up to us to make sure that they get the right foods to keep them in good health.

Author: Dave Wilson
First published in Tank Talk, Canberra and District Aquarium Society, Australia
Source: (no longer available)

Last Updated on 14 March 2020 by John

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