A new fish species from Lake Victoria named in honor of the author of Darwin's Dreampond

In 1985, Leiden biologists made a survey in the Tanzanian part of the lake, with an old ferry as floating lab, to establish the status of the rapidly declining cichlids. During this expedition Tijs studied the egg spots on the anal fin of cichlids for their possible role in the rapid speciation of these fish. In the Emin Pasha Gulf, among a species nicknamed Haplochromis "argens," individuals were found with aberrant egg dummies and lacking red in the fins. Just the kind of example Tijs was looking for to test his theory of speciation by sexual selection. The aberrant individuals were provisionally named H. "dusky argens."

Both "species" play a part in Tijs' PhD thesis and in other studies. However, a taxonomic description was never made and whether H. "dusky argens" was a separate species or a colour morph remained unclear. In 1987, most cichlid species from the offshore waters of the lake had disappeared, and with them the urge of taxonomic descriptions.

Now, 25 years later, about a quarter of the cichlid species have recovered in the "Nile perch desert," some of them became even more abundant than in the past, but the former common H. "argens" is still extremely rare. The status of H. "dusky-argens" is unknown as it was only caught in the remote Emin Pasha Gulf, which is not sampled nowadays. Research on successfully resurgent species shows that they were able to adapt morphologically to the new environmental conditions. Their body shape, for instance, changed, so that burst swimming to escape predators improved. Preliminary results suggest that such a response is not found in H. "argens."

The above observations triggered the present taxonomic study as a baseline for further research. It shows that several taxonomic characters differ more between the co-occurring populations of H. "argens" and H. "dusky argens" in the Emin Pasha Gulf, than between populations from different locations. This suggests that they are indeed two species, which are morphologically driven apart at places where they co-occur. In case of H. "argens" the nickname was upgraded to the formal name, while H. "dusky-argens" is now named H. goldschmidti.