Trophic Relationships of Limnoperna Fortunei with Adult Fishes

Abstract

In South America, the inventory of species that feed on Limnoperna fortunei has increased steadily; in 2006, 18 fish species had been identified as predators of L. fortunei, whereas 7 years later, the list had grown to almost 50 species. In some areas, fishes that consume L. fortunei represent > 50 % of the species regularly present in commercial fisheries, including traditionally omnivorous, iliophagous, and ichthyophagous forms. Several economically important species have significantly changed their feeding habits since the mussel’s introduction, shifting from a diet based on plants and detritus to one dominated by adult mussels. Consumption of golden mussels is not restricted to fishes provided with teeth that can crush and grind the shells; many toothless species swallow whole specimens or nibble on the exposed siphons and mantle edges of the bivalve. Golden mussels can account for up to 100 % of the gut contents of some fish species, especially during the summer. Feeding of fishes on L. fortunei often involves the selective consumption of the smaller mussel size classes. Fish predation pressure on the mussel is likely high and it probably represents the most significant mechanism that modulates L. fortunei populations, but it is very unlikely to eradicate the mussel altogether. No comprehensive, large-scale studies are yet available on the effects of this new food supply on local fish stocks, but ancillary information suggests that these effects are likely very significant. Impacts are not restricted to species that consume the mollusc, but also affect species that benefit from this new food resource indirectly, including large ichthyophagous species feeding on molluscivorous forms, as well as on those that consume the organic matter-enriched sediments by the mussel’s feces and pseudofeces.