Spatial distribution of exotic fish species in the Guadiana river basin, with two new recordsThis work updates the spatial distribution of the exotic fish species in the Guadiana river basin. To this effect, 241 river stretches and 37 reservoirs and lakes were sampled, corresponding to 261 UTM 10 × 10 Km squares. A total of 12 exotic species were found, including two new species that had not been previously cited in the area, the channel cat-fish (Ictalurus punctatus) and the roach (Rutilus rutilus). These two species, related to lentic systems, had a very restricted distribution in the basin, probably as a consequence of its recent introduction. The expansion of the remaining exotic species was also confirmed. Some species as the pumpkinseed sunfish (Lepomis gibbosus), the mosquitofish (Gambusia holbrooki) or the largemouth bass (Micropterus salmoides) have become common components of the fish community, not only in reservoirs but also in lotic systems.

The interactions between bullhead (Cottus gobio), stone louch (Borbutulu bnrbatulu) and gudgeon (Gobio gobio) and subsequently their influence on the exclusion capacity of these species were examined in laboratory experiments. When a combination of gravel, sand and sand plus shelters substrate types were offered, the three species selected sheltered substrates. This preference was stronger when the three species wcre together rather than when in allopatry. None of the species showed any preference to coexist with another under sheltered positions. When only one specics occupied a sheltered position it was alone, without any other conspecific. Dispersal patterns differed bctween species but during this process there was no evidence of any species association. This study highlights a very limited interspecific interaction between bullhead, stone loach and gudgeon, and shows that intiaspccific exclusion in these species was much more important than the interspecific one.