What is an OB morph?

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Some African cichlids are available as OB morphs. Professor George Turner explains what they are.

OB morphs are naturally occurring colour forms of certain African cichlids. They are found in several lakes, including Victoria, Kivu and occasionally Tanganyika.

However most OB fish in the trade are from Lake Malawi where they occur in the Pseudotropheus zebra group  (sometimes called Maylandia or Metriaclima), Tropheops, Labeotropheus and the fin biter Genyochromis.

In the wild, 99% of OBs are females.

This is an example of a natural colour polymorphism, where the OB and the ‘normal’ — sometimes called the BB form — are found together in the same population of fish.

This is almost certainly something to do with appearance, because OB forms are always found in shallow clearwater habitats. Mate choice, competition and predation are all possible factors.

The blotchy pattern seems to be a disruption to the process of distributing the dark melanin pigment.

Instead of being evenly spread over the body, the melanin cells are concentrated in dense dark blotches, leaving the underlying yellow or orange colour to show through in gaps between.

Fish with very few blotches are sometimes called O-morphs.

OB fish are perfectly natural and healthy and will readily interbreed with each other and with the normal form of the same species.

This article was first published in the December 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.