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Nimbochromis polystigma
by Paul Haese

The Nimbochromis polystigma is also traded as Haplochromis polystigma or just polystigma.


Habitat

Male Nimbochromis polystigmaIt is endemic to Lake Malawi and can be found in all reaches of the lake. There is some conjecture that two separate species inhabit the lake. Authors such as Ad Konnings disagree with this notion, and are of the belief that only one species are present throughout the lake.

Despite this, the polystigma can most commonly be found in and around areas of medium to dense aquatic vegetation. The reason being that this fish is a piscivore, meaning that its primary diet consists of other fish and in particular small, unwary fry. It will use this vegetation from which to launch its ambushes.


Behavior

In the Lake the polystigma often can be found hunting in packs, although single fish at times can be seen hunting on their own. Despite the latter, it seems that these fish display an organised habit in relation to acquisition of food.

Like all the Nimbochromis family, this fish can be seen at times lying quite still on its side, looking very dead. This is not a pleasant sight and can be quite disconcerting for the keeper of this quirky fish. The polystigma uses this behaviour as a hunting tactic, to attract smaller, witless fish. As the prey nears the "dead fish", the polystigma will quickly dart towards its prey and swallow it whole.

Female Nimbochromis polystigmaAside from its hunting habits, this fish cannot be deemed as an aggressive fish in the writer's experience. In fact it acts for the most part as a benevolent neighbour to those that are not edible.

Its comical nature becomes obvious at feeding time. Like its South American cousin the Oscar, it will jump for its food. Looking more like a miniature dolphin, attempting to reach the food first. Care should be taken when checking the "smell" of the tank. You should not get your nose too close or you will end up with a polystigma attached to it!


Description

This fish can be described as one of the heavyweights of the aquarium. It will grow (in the wild) to lengths of 23cm. In an aquarium it has been known to reach nearly 30cm or one foot. It is for this reason that this fish should not be left in a tank with inhabitants that are "mouth size"; it will devour all these fish within days if not hours.

Despite this, the polystigma is an underrated fish. Both juvenile males and females are adorned in a brown, leopard-like pattern that only changes in the case of males as they reach adulthood. Males will then display in what can be described as a magnificent mating dress. The drab spots are replaced by an intense green-blue throughout the body and the head is adorned with a wondrous green-gold, topped with iridescent golden lips (See photo). Male Nimbochromis polystigmaThe dorsal and anal fins are resplendent with golden yellow flashes or in some specimens red.

Males will commence adult colouration anywhere between nine and twelve months of age. Colouration should be complete within one year. This will depend upon whether there as other males present and which one is dominant. Females will maintain the basic colouration for the duration of their lives.

Theories regarding the colour pattern of the polystigma revolve around the central notion of camouflage. Firstly, the pattern can be seen quite distinctly in fry that are days old. The pattern can be said to act as a disruptive element to body shape and therefore act as a defensive mechanism against opportunistic predators. Secondly, the pattern as seen in adults acts in two capacities. Adults will employ the pattern to disguise their presence among the reeds and sedimentary rocks when hunting. The other is where the polystigma can use the pattern to appear as a rotting corpse. When acting in this manner, the lighter skin becomes quite pale and the spots appear as dark blemishes.


Recommendations

Given the potential for size this fish should not be kept in a tank less than 350 litres (100 gallons).

It should be kept with inhabitants of equal size.

Breeding rocks should be laid flat or an area set aside where a pit can be constructed by the amorous male.

Fry should not be left in the tank with the adult after two to three days.

Enjoy this fish as I have. □

 

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