AB 19:1-11 (2013)  -  DOI: https://doi.org/10.3354/ab00512

ABSTRACT: Interspecific interactions can affect the long-term viability of endangered fish species. The present study analyses the interactions in trophic ecology between the endangered Iberian toothcarp Aphanius iberus and the highly invasive eastern mosquitofish Gambusia holbrooki at a sympatric site where they have been verified to coexist for more than 10 yr. The existence of a habitat gradient in the system, mainly determined by salinity and accompanied by different proportions of the 2 fish species, made it possible to analyse dietary variation along that gradient. Overall results from gut content analysis showed a high degree of similarity in the spring diets of both species. However, the mosquitofish appeared to be a better competitor for food resources, as individuals of this exotic species presented a lower proportion of empty guts and their guts contained more food. Possibly associated with a certain degree of spatial segregation, a shift in the diet composition of the toothcarp and the mosquitofish was observed among sites with different salinities and relative abundances of both species. In general, in sectors of the channel with lower salinity levels and mosquitofish as the dominant species, toothcarp seemed to display more benthic feeding and, consequently, the diets of both species were less overlapped. Under such conditions, the toothcarp diminished feeding intensity and diet diversity. Thus, this native species could be subjected to a decrease in its population viability as a direct consequence of trophic relationship with the invasive fish.

KEY WORDS: Aphanius iberus · Gambusia holbrooki · Diet · Trophic ecology · Interaction