Fish Species at

Red Rainbowfish

Red Rainbowfish (Glossolepis incisus) information and care.

By Mike Wickham

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Aquarium Fish International Magazine
The rainbowfishes of Australia and Papua New Guinea have become some of the most treasured fish in the hobby. They are noted for their many colors, high levels of activity and hardiness as citizens of the aquarium.

Perhaps the granddaddy of all rainbowfishes is the red rainbowfish (Glossolepis incisus), also called the red Irian rainbow. Glosso is from the Greek for “tongue,” and lepis is Greek for “scale,” referring to teeth on the fish’s tongue. Incisus also comes from Greek, meaning “deeply cut.” This probably refers to the crease that develops on mature males, between the head and nuchal hump.

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Red Rainbowfish feed in schools, making it important to group them with other fish
Red rainbowfish (Glossolepis incisus) are schooling fish, so keep them in groups of six or more in a large enough aquarium. Photo by Tony Terceira.
The red rainbowfish is spectacular, growing to nearly 6 inches in length. Females and juveniles have streamlined bodies with a sort of olive overcast, but the scales catch the light, reflecting silver. Males are much more impressive. The entire body and fins become flushed with color varying from dark orange to deep red, depending on the specimen and diet. Mature males also develop a nuchal hump. As males grow, the whole body appears to widen vertically — they get “taller” — until the streamlined shape is gone. What emerges is a fish shaped more like a freshwater sunfish with a pointy nose.

In the Wild
Red rainbowfish come from Lake Sentani and surrounding streams in the Irian Jaya region of western Papua, on the island of Papua New Guinea. They prefer water with an alkaline pH from 7.2 to 7.8 and a bit on the hard side, with a temperature of 72 to 75 degrees Fahrenheit (22 to 24 degrees Celsius). However, the fish is hardy, and hobbyists should have no problems keeping it in most common aquarium conditions.

The Rainbowfish Aquarium
The red rainbowfish is a schooling species. The fish are happiest and best enjoyed in groups. I would not keep less than three (two females and a male), and groups of six or more would be better. Recalling that this fish grows to nearly 6 inches, a large aquarium is in order. I would not recommend keeping this fish in an aquarium of less than 29 gallons in size. Aquariums of 55 gallons or more are more in order to truly enjoy a group of red rainbows. A heavily planted 125-gallon aquarium with two dozen red rainbowfish would be truly impressive.

Natural aquariums that are heavily planted, and decorated with driftwood and a few large rocks are the best way to display the red rainbowfish. Such decor brings out their colors. The red of the fish and the greens of the aquatic plants are opposites on the color scale, accentuating the appearance of the fish. One of the best rainbowfish displays I ever saw added a powerhead at the front of the aquarium, with the output directed across the length of the front glass. The rainbows loved to play in this stream, and it had the added advantage of bringing them right up to the front glass for easy viewing. The effect could also be achieved by directing the output from a canister filter.

All the colors of the rainbow can be found in various rainbowfishes (hence the name), and some species show all the colors, depending on the angle of light hitting them. The red rainbowfish, of course, is primarily red. This fish looks good under any aquarium bulb but especially under bulbs that have a peak in the red part of the spectrum that really highlights red fish. The fish look more red and less orange. You may want to consider using such a bulb to bring out the best colors in your fish. In heavily planted aquariums, some hobbyists use full-spectrum lights at the back for the aquatic plants but use a red bulb at the front to accentuate the fish.

Rainbowfishes are omnivores, but their primary diet is insects, both those that fall into the water and those that are aquatic. Stomach contents show that a large part of the diet in the wild is ants. Many fish won’t eat ants, due to the high formic acid content, but rainbowfishes don’t mind. You may want to try some ants as a treat. Otherwise, all the usual recommendations apply. First, feed variety. Live, frozen, and freeze-dried foods are best, but red rainbowfish happily eat flakes. Color-enhancing flakes are a good basic choice.

A varied diet is important. Rainbowfish are hardy and disease-resistant, but one unusual thing I have seen in them is the development of goiters. It manifests when you see a small bit of tissue hanging out of one gill. Goiters are generally related to diet deficiencies, particularly of iodine. So it may be wise to add some algae flakes to the diet to help supplement. Algae, especially marine algae, are natural accumulators of iodine.

The red rainbow breeds readily. A common method is to set up a trio (two females and one male) in a 29-gallon or larger aquarium at 78 to 80 degrees Fahrenheit (25 to 26 degrees Celsius). As always, it is best to condition males and females separately. Absence makes the heart grow fonder upon reintroduction. Add some large clumps of Java moss to receive the eggs. Water should be hard and alkaline, as described earlier.

Red rainbowfish scatter adhesive eggs in the aquatic plants. A female will lay up to 50 of them per day. Breeding usually occurs in the morning. Males display for the females and then drive them into the aquatic plants, where the release of eggs and milt takes place. To prevent them from being eaten, remove the Java moss each day and check it for eggs. You can then break off the bits of moss with eggs attached and move it to a separate aquarium for hatching and rearing. Eggs are about 1 millimeter in diameter, and they hatch in six or seven days. Powdered egglayer food, infusoria or microworms can be offered as a first food.

I hope this information encourages you to try your hand at keeping rainbowfish in your home aquarium. A school of red rainbowfish can make a spectacular display. Happy fishkeeping!

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