A survey of the Fish Fauna of Sudanese Irrigation Systems with Reference to the Use of Fishes in the Management of Ecological Problems (the Control of Aquatic Weeds, Malaria and Infective Schistosomiasis)

This paper reports on a fundamental study of the fish fauna already present within the irrigation canals. The fauna was investigated with a view to determining its use in the control of nuisance biota. Twenty-seven species of fish were collected, comprising 22 genera and 12 families. This fauna is closely allied to the fauna of the source water, the Blue Nile. Several Blue Nile species are absent and some of those collected are new recordings for the area. Each species of fish collected had neither a suitable feeding habit nor a wide enough distribution to have any significant effect on the levels of nuisance biota. This includes the mosquito fish. Gambusia affinis, which was specifically introduced for mosquito control. Improvement in the ecological conditions within the canals involves both the management of the already-existing fish stocks and the introduction and management of additional species. A reduction in the levels of aquatic weeds using phytophagous fishes should be a high priority with malacopliagous and larvivorous species also being introduced and their stocks managed. Species suitable for introduction, which are generally endemic to the Nile system, are suggested. The fish species diversity falls as the canals become smaller and the water within them subject to much greater variations in flow and quality. The lowest order canals (field canals) are probably unsuitable for permanent fish stocks. The nuisance biota within field canals can be controlled by simple improvements in crop-watering procedures. The widely distributed and diverse fauna found within minor canals suggests that problems due to fish-kills brought about by heavy pesticide and herbicide usage are not so severe as previously thought. The management of the ecological problems is a complex task due to the interrelationships of many factors.