Parasites of the fish Cichla piquiti (Cichlidae) in native and invaded Brazilian basins: release not from the enemy, but from its effects.

Abstract

The enemy release hypothesis is frequently used to explain the success of invaders, postulating that introduced species have escaped from their native enemies, including parasites. Here, we tested this hypothesis for the tucunaré (Cichla piquiti), a predatory cichlid, and its endoparasites. First, the parasites and their influence on the condition of the hosts in the native environment, the Tocantins River (TO), were compared to an environment where the fish was introduced, the Paraná River (PR). Then, comparisons of the abundances of Diplostomidae eye flukes and Contracaecum sp. larval nematodes were made between the introduced tucunaré and two predators native to the PR, Hoplias malabaricus and Raphiodon vulpinus. Nine species of endoparasites were recorded in total, five of which occurring in both localities. Total species richness did not differ between localities, and fish condition was negatively affected by the cestodes Sciadocephalus megalodiscus only in the TO. In the PR, abundance of Contracaecum sp. did not differ between natives and invaders; however, eye flukes were more abundant in the native fish H. malabaricus, which may represent an advantage to the invader if they were competing for prey. These results did not support the idea that the escape from parasites favoured the establishment of C. piquiti in the PR. Instead, the escape from the parasites' effects seems a better explanation, and further studies examining effects on host physiology and/or fitness in the native and introduced ranges are needed.