Effects of cage fish farms on functional diversity of wild fish communities in a Neotropical reservoir

Abstract

Caged fish farms provide continuous organic matter input to the aquatic environment. This available resource can be used, directly or indirectly, by the ichthyofauna around the cage, remodeling the community and making it functionally impoverished. The research aimed to test the hypothesis that cage fish farms located in a Neotropical reservoir cause functional simplification of the wild ichthyofauna. Samplings were carried out at three sites of cage fish farms and their respective three control sites, dividing them into three areas (one cage fish farm site and one control site each) located in the Chavantes Reservoir, Paranapanema River. A total of 9765 individuals were collected, divided into 31 taxa, from five orders and 15 families. To test the hypothesis, functional richness (FRic), evenness (FEve), redundancy (FRed), functional β diversity, and the community-weighted average of an attribute (CWM) were analyzed. The results showed that despite the high FRic value, the communities proved to be less uniform and more functionally redundant, in addition to having few functional substitutions. Functional attributes related to diet were more important for the difference in functional diversity between sites. Thus, although community simplification did not occur as we hypothesized, functional diversity was influenced by the changes that cage fish farms promote in the aquatic environment, especially in food availability. Our expectations were partially met; cage fish farms can favor specific functional attributes, such as a detritivorous/omnivorous diet, which benefit from the resources made available by these systems. Consequently, the ichthyofauna on a local scale may become functionally redundant, and functional disruption may occur in this ecosystem since, from a trophic point of view, few functional attributes are prevalent, such as omnivores and detritivores. However, from an economic point of view, fishing can be favored, considering the predominance of important species for fisheries.