Observations on the Biology of Chaoborids and Chironomids in Lake Victoria and on the Feeding Habits of the Elephant-Snout Fish' (Mormyrus kannume Forsk.)

Abstract

During the course of work on the bottom fauna of Lake Victoria in relation to the feeding habits of fish, the opportunity was taken to make some observations on the biology of Chaoborus, the larvae of which, although relatively unimportant as fish food, are perhaps the most abundant mud-dwelling insects in the lake. Since practically no data are available on the effect of tropical lake conditions on the development of these insects, attention was paid mainly to the length of the lifecycle. In the mud with the Chaoborus were various species of chironomids, and of these, Tanypus, Procladius and Chironomus larvae were the most common. These larvae form an important part of the food of Mormyrus kannume Forsk. (the 'elephant-snout fish'), and it was necessary to know more about their biology. In the general features of their life-cycles they resemble Chaoborus, and for this reason they are being treated together. It is worthwhile also to discuss the relationship between the insect larvae and Mormyrus kannume, because a study of the food preferences of the fish throws some light on the biology of the insects, and, at the same time, features of the insect biology explain some apparent peculiarities of the fish diet.