Testing the enemy release hypothesis in the invasive fish Amatitlania nigrofasciata (Perciformes: Cichlidae) in Mexico

Abstract

The enemy release hypothesis (ERH) posits that invasive species are released from their natural enemies in their invasive range, which promotes their successful invasion. In this study, we tested the ERH in a population of the convict cichlid Amatitlania nigrofasciata, an invasive species in Mexico. The ERH predicts that the convict cichlid: (a) is not infected by specialist helminth parasites in the invasive range; (b) has lower infection parameter values, as measured through richness, prevalence, abundance and diversity of helminths, than a native species—the redside cichlid Cichlasoma istlanum; and (c) is not affected in its condition factor by the abundance of helminths it carries. The convict cichlid was infected by two (33%) specialist helminths relative to the six specialist helminths that infect the cichlid in its native range. The convict cichlid had lower helminth richness and diversity than the redside cichlid. However, the prevalence and abundance of the par- asite species varied between the host fish. While the prevalence and abundance of the nematode Rhabdochona kidderi was higher in the redside cichlid, the prevalence and abundance of the trematode Uvulifer sp. was higher in the convict cichlid. The condition factor in both host fish was not correlated with helminth abun- dance. Our results do not agree with the prediction that the convict cichlid is completely released from spe- cialist parasites, nor with the prediction that this invasive species has lower infection parameter values than the native redside cichlid. However, our results agree with the prediction that the abundance of parasite hel- minths do not affect the cichlid’s condition factor. More studies are necessary to determine the advantages that the convict cichlid could have in the invasive range when it is infected with a low richness and diversity of helminths.