| Summary: | The distribution and apparent habitat preferences of the common mummichog (Fundulus heteroclitus) in southwestern Spain were examined during summer-fall 1996. This introduced species was more or less continuously distributed along the Atlantic coast of Spain, being more abundant in sites near the coastline (usually < 10 km inland), mainly in four extensive marshes. The species preferred marsh-related mesohabitats, such as salt lagoons, salt marsh fish ponds and marsh channels, both natural and man-modified. F. heteroclitus was mostly found at salinities > 25. It was the most frequently captured fish species, occurring at 81 of the 272 sites sampled; their frequency of occurrence was almost twice that of the second ranked species (Gambusia holbrooki). However in over 80 % of cases, F. heteroclitus was found alone or with only one sympatric fish species, which usually belonged to a group composed of Gobius niger, mugilids, Anguilla anguilla, Blennius sp., Lebias ibera, Pomatoschistus sp. and Dicentrarchus labrax. Finally, we discuss the origin and dispersal of mummichog in the Iberian peninsula and the potential effects of this species on native fish populations is discussed.
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