Ecological problems associated with irrigation canals in the Sudan with particular reference to the spread of Bilharziasis, Malaria and Aquatic weeds and the Ameliorative role of fishes

Abstract

Biological problems associated with irrigation canals in the Sudan are discussed. These problems are primarily the proliferation of aquatic weeds and the water‐borne vectors of the diseases bilharzia and malaria (i.e. snails and mosquito larvae, respectively). The differences in hydrobiological conditions between the natural source water and the water impounded within canals are fundamental to the understanding of the problems that arise. Ecological management of the canals involves reductions in the levels of weeds, snails and mosquito larvae in a cost‐effective yet environmentally acceptable way. Other concerns are at present secondary. Data on the importance of the resident biota is lacking. Biological control agents, and especially fishes, have a major role to play in management. Scope exists for species introductions. Such introductions should be carefully monitored and the effects on non‐target as well as target problems recorded, including relevant interactions with the resident biota. In particular, the interrelationships between the effects of any introduced phytophagous fishes and the levels of the vectors of diseases needs careful study. Problems with heavy usage of pesticides and herbicides in the irrigated areas are discussed. The control of aquatic weeds and the vectors of diseases and the heavy usage of chemicals in irrigated areas in the tropics should be subject to an integrated approach.