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

Life-cycles of Chaoborus anomalus and an undetermined sp. of Chaoborus were found to last 2 mos. Larval life comprised 4 instars of which 1st 2 were planktonic, and 3d and 4th were mud-dwelling by day and planktonic by night. Tanypus guttatipennis and Procladius umbrosus had life-cycles lasting 2 months. There were 2 populations of each spp. separated in time by 1 month. As result, emergences occurred at regular monthly intervals. Length of life-cycle of Chirono-mus sp. was possibly 2 months or certainly a multiple of 1 month. Since these 5 spp., and a number of others, emerged regularly about time of new moon, it is suggested that there may be a lunar influence. Large "lake-fly" swarms occurred during period when moon was waxing; peak of emergences was 2-3 days after new moon. Regular fluctuations in spp. of larvae which formed principal food of Mormyrus kannume were correlated with fluctuations of same spp. in mud.