Fish species of the lower Zeeschelde (Belgium) : a comparison with historical checklists.

In the 19th century approximately 40 fish species (excluding freshwater species) were recorded in the lower Zeeschelde between the Dutch/Belgian border and Antwerpen. In comparison with the 19th century and the first half of the 20th century the total number of fish species in the Beneden-Zeeschelde has decreased considerably. The present checklist (1991-1993) of fishes of the lower Zeeschelde (excluding freshwater species) contains only 26 species. The fish community is composed of marine species (13), catadromous species (3), estuarine residents (9) and one anadromous fish species. Besides, 6 freshwater fish species have presently been recorded. The distribution of diadromous fishes, estuarine residents and freshwater fishes is probably greatly affected by low oxygen levels in the lower Zeeschelde, whereas the disappearance of adventitious marine species is probably also the result of anthropogenic effects on a much wider geographic scale. A comparison was made with recent and historical checklists of fishes of the Westerschelde and the Oosterschelde (the Netherlands).