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The Rhine may provide a classical example of faunistic changes due to Man-made stress. Formerly a salmonid river, it was transformed into a ship-canal. Steadily increasing pollution culminated in the 1960s and 1970s. An improvement of water quality in the 1980s was followed by an increase in abundance of several species and faunal diversity. Originally 47 species inhabited the Rhine; at present 40 indigenous and 15 introduced species live in the river, seven have vanished or have not been observed so far. Recent setbacks, like the Sandoz Accident in 1986 failed to eliminate any taxon. Protection of the indigenous fauna is t o be linked with conservation of remaining environmental diversity, ecotechnical improvements, and new strategies in fishery management, which do not merely support only economic species. KEY WORDS Rhine Fish community Predator-prey Pollution Cyprimids Conservation Human impact INTR 0 D UCTI 0 NThe Rhine River is one of the most anthropogenically stressed water courses in Europe. Its natural flow has been channelized for more than 100 years. The floodplain area, with the exception of some stretches, has almost completely lost its ecological function. In the 1960s and 1970s the river was on the brink of total deterioration because of all kinds of pollution. The results of investments in water purification plants on the Rhine itself and in its catchment area proved positive. The abundance and diversity of species has improved in the last 10 years. However, in November 1986 a heavy pollution wave-the Sandoz Accident-occurred in the course of fire-extinguishing activities at a burning storehouse containing insecticides and fungicides. This seemed to be detrimental to the fish fauna, at least in upper reaches (Upper Rhine) of the river. This paper examines fish occurrence two years after Sandoz. METHODS AND AREA UNDER EXAMINATIONThe principal method of taking fish samples was by electrofishing device. A 'DC' electrofishing gear (Fa. DECA) was deployed mounted on the research boat 'Rutilus'. The output of the gear varied between 5 A and 15 A and 230 V and 600 V according to the electrical conductivity of the water. In shallow tributaries and weeded shorelines of the backwaters, portable gear (DECA 3000) was used. The fishes were narcotized with an electrified anode, a metal dipnet of 42 cm diameter and a meshsize of 0.5 cm (bar). As a rule, the shoreline of every station was fished allowing samples to be taken to a maximum depth of 1.5 m. Fishing in 'open water' generally yielded only a very limited catch. As far as the general occurrence of species is concerned, information from artisanal and sport fishermen was taken into account, provided they could prove their catch. In the stagnating and deep waters of harbours, fish traps were also used.The fish catch was identified mostly in the field or preserved. The following parameters were recorded: standard length (mm or cm), individual weight (g), actual fishing time (min.), length of the fished stretch (m). Samples were taken from the city of Basel, S...

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The recently established large reservoirs Manantali on the river Bafing, tributary to the Senegal River and Selingue, located on the river Sankarani, tributary to the Niger River, have followed similar changes in limnology and fish populations as those established in West Africa 20 to 30 years ago. Basic water parameters, such as oxygen content, pH, electrical conductivity and temperature show seasonal variations largely determined by the changes in wet and dry seasons. Both waterbodies are monomictic, with water mixing taking place in January, the coldest period ofthe year. Pre-impoundment forest clearence ofthe future reservoir bottom in the shallow SelinguC reservoir was carried out only in the proximity of the dam site. In the deeper reservoir Manantali the savanna forest was cleared from an area of about 25 percent, and the tree gallery was cleared along the river. The initial filling of Manantali reservoir was followed by a nearly complete drainage of the reservoir. After refilling some months later, the dissolved oxygen content stayed reasonably high and therefore there was no fish mortality. Also no hydrogen sulphide or a large-scale spread of noxious aquatic plants developed. At present the fish fauna is dominated by cichlids and pelagic species, i.e. at SelinguC by clupeids, and at Manantali by cyprinids (Lepfocypris niloticus). In both reservoirs was the genus Citharinus considerably reduced. At Selinguk reservoir disappeared Proroprerus annectens. The fish yield estimate is 27 kg/ha/year for Manantali, and 40 kg/ha/year for Selingue. Both rerservoirs have recorded a slight increase in electrical conductivity. They both serve as a valuable water resource and fish supply for the Sahel region.