Cage fish farming as a driver of changes in the functional diversity and structure of ichthyofauna in a Neotropical reservoir

The Upper Parana River Basin has the highest number of impoundments in South America. These provide areas for cage fish farms, which can have environmental impacts related to the release of organic matter into aquatic ecosystems. Despite the importance of using functional diversity analysis, no study has performed this type of assessment for freshwater environments. The aim of the present study is to establish whether (1) cage fish farming has caused functional impoverishment of local ichthyofauna; (2) modifications in functional diversity are mainly related to the diet of the fishes; and (3) cage fish farming has caused taxonomic re-structuring of the local ichthyofauna. Two areas of the Ilha Solteira Reservoir were surveyed, a cage fish farm and a control area located 10 km upstream of the fish farm area, and their wild ichthyofaunas were compared. Functional diversity, taxonomic diversity, and multivariate analyses were carried out. Traditional taxonomic diversity indices did not detect significant differences between the fish communities in fish farm and control areas. However, a significantly lower functional diversity and homogenization of eating habits in the fish community from the fish farm area was observed, just as there were changes in the structure of the ichthyofauna, caused by different dispersions of species abundance between areas. The present study highlights the necessity of using different evaluation methods and multifaceted diversity approaches to evaluate the environmental impact of fish farming.