Abstract: This study compared the structure and composition of the parasite communities in Callichthys callichthys and Megalechis thoracata of a tributary of the Amazon River system, northern Brazil. A total of 447 parasites was collected from 38 specimens of each host, and 44.7% and 36.8% of fish species respectively were found to be infected with 1 or more species of parasite. The similarity in parasite assemblages between hosts was high (61%) with both infected at similar levels by Genarchella genarchella, larvae of Eustrongylides sp., Rhabdochona sp. and plerocercoids of Proteocephalidae. However, the dominant parasites found in C. callichthys were metacercariae of Posthodiplostomum sp., which did not infect M. thoracata. In M. thoracata the dominant parasite was G. genarchella, and this host species was also infected by Gorytocephalus spectabilis which did not infect C. callichthys. The parasite communities were dominated by endoparasites, and species richness of parasites, Shannon diversity index and evenness were similar for both hosts. The results indicate that these fish species are intermediate hosts of the endohelminths found. Finally, the variation in the parasite community between sympatric hosts occurred probably due to the hosts’ distribution in the environment and the diet of each host species.

Resumen: Este estudio comparó la estructura y composición de las comunidades de parásitos de Callichthys callichthys y Megalechis thoracata en el afluente del río Amazonas, al norte de Brasil. Un total de 447 parásitos se recolectó de 38 ejemplares de cada hospedero; 44.7% y 36.8%, respectivamente, estuvieron infectados con 1 o más especies de parásito. La similitud en los ensambles de parásitos entre estas 2 especies de hospederos fue alta (61%) debido a que ambas presentaron niveles de infección similares de Genarchella genarchella, larvas de Eustrongylides sp., Rhabdochona sp. y plerocercoides de Proteocephalidae. Sin embargo, Posthodiplostomum sp. fue encontrado solamente en C. callichthys, mientras que Gorytocephalus spectabilis fue encontrada en M. thoracata. Sin embargo, los parásitos dominantes en C. callichthys fueron metacercarias de Posthodiplostomum sp., las cuales no se encontraron en M. thoracata. En M. thoracata el parásito dominante fue G. genarchella, este hospedero también estuvo infectado por Gorytocephalus spectabilis, que no se encontró en C. callichthys. La mayoría de las infracomunidades de parásitos presentaron un patrón de dispersión agregado. Las comunidades de parásitos estuvieron dominadas por endoparásitos; la riqueza de especies, el índice de diversidad de Shannon y la equidad fueron similares para ambas especies de hospederos. El tamaño corporal de C. callichthys y M. thoracata no fueron influenciadas por los bajos índices de parasitismo. Finalmente, la variación en la comunidad de parásitos entre estas 2 especies de hospederos simpátricos se debe probablemente a la distribución de los hospederos en el cuerpo de agua y a la dieta de los hospederos.

RESUMO Este estudo investigou a fauna de parasitos metazoários em Peckoltia braueri e Pterygoplichthys pardalis de um tributário do sistema do Rio Amazonas, no Amapá, norte do Brasil. Em P. braueri foram coletados 630 parasitos das espécies Unilatus unilatus, Nothogyrodactylus sp., Genarchella genarchella, Proteocephalus sp., Gorytocephalus elongorchis, Dolops longicauda e Hirudinea gen. sp., com dominância das espécies de monogenoideas. Em P. pardalis foram coletados 120 parasitos das espécies U. unilatus, Acanthostomum gnerii e Gorytocephalus elongorchis, sendo este acantocéfalo a espécie dominante. Os parasitos em ambos hospedeiros apresentaram dispersão agregada, elevada prevalência, baixa abundância, baixa diversidade de Shannon e baixa riqueza de espécies, com predominância de espécies de helmintos. Em P. braueri, o comprimento dos hospedeiros apresentou correlação positiva com a riqueza de espécies de parasitos e o índice de Shannon. Não houve diferença entre a condição corporal de peixes parasitados e não parasitados para os dois hospedeiros. Este foi o primeiro relato desses parasitos para P. braueri e P. pardalis.

ABSTRACT This study investigated the metazoan parasite fauna in Peckoltia braueri and Pterygoplichthys pardalis from a tributary of the Amazon River system, in northern Brazil. In P. braueri, 630 parasites were collected, belonging to Unilatus unilatus, Nothogyrodactylus sp., Genarchella genarchella, Proteocephalus sp., Gorytocephalus elongorchis, Dolops longicauda and Hirudinea gen. sp., with a dominance of monogenean species. In P. pardalis, 120 parasites were collected, belonging to U. unilatus, Acanthostomum gnerii and Gorytocephalus elongorchis, and this acanthocephalan was the dominant species. In both hosts, the parasites presented clumped distribution, high prevalence, low abundance, low Shannon diversity, and low species richness, with a predominance of helminth species. In P. braueri, host length was positively correlated with parasite species richness and Shannon index. There was no difference in the body condition of parasitized and non-parasitized fishes in either host. This was the first report of these parasites in P. braueri and P. pardalis.