We tend to think of male fish as being the brighter of the sexes, but this isn’t always the case. Uwe Werner looks at a species famed for its extravagant females.
Nanochromis transvestitus is as curious as it is gorgeous. It’s an African dwarf cichlid which I heartily recommend to any aquarists with experience in keeping similar species. There’s a reason I’m wary about suggesting them for all aquarists though: in spite of their small size (which doesn’t exceed 6cm) they can display a degree of aggression an order of magnitude greater than their small statures suggest. And, should you wish to breed them, you will need to provide soft and acidic water.
Breeding is something you definitely want to try. In their reproductive dress, the females are real beauties. Their cherry-red bellies form a striking contrast to their distinctly black and white striped fins, and unlike most cichlid courtships it’s the females that do the work of displaying to potential mates, as they twist their bodies in a fascinating dance to allure the males they want to spawn with.
Acidic lake homes
The type locality of Nanochromis transvestitus is Lake Mai-Ndombe, formerly called Lake Inongo or Lake Leopold II, which is situated in the Congo (previously Zaire) basin. In 1973, ichthyologists Donald Stewart and Tyson Roberts carried out an ichthyological survey on the southern shore of the lake, the shallow water of which drains into the Fimi River, formerly called the Lukenie, which in turn flows into the Kasai, the largest southern tributary of the Congo.
The water of the Mai-Ndombe itself is so black that if you submerge your hand in it, it becomes impossible to see at some 20-30cm depth. It stands to reason that such tannin-stained water is also very acidic, and N. transvestitus can be found living in locations with a pH of just 4.0.
The lake shore is composed of porous rock and uprooted trees that have fallen into the lake everywhere. In areas where rocks are absent, the bottom is covered by layers of hard-packed fine sediment and rotting vegetation. Freshwater sponges of the genus Spongilla with hard, sharp edges grow on the rocks and trees along the shore.
Stewart and Roberts noted that the most brightly coloured Nanochromis were found in dark, rocky areas, where they occurred in large numbers; they came across as highly territorial and seemed to form themselves into colonies.
Stomach examinations of individuals from their natural habitat have revealed that they eat benthic invertebrates, particularly Cladocera (water fleas), midge larvae, mites, and detritus as well as large quantities of pieces of sponges. Their teeth are quite appropriate for this: the teeth in the jaws are conical with brown tips and arranged in two rows, while the pharyngeal teeth (within the throat) have a large, slightly curved primary cusp and at least one smaller secondary cusp.