The aim of this study was to compare the parasite communities in two sympatric host populations, Trachelyopterus coriaceus and Trachelyopterus galeatus, which were caught in tributary of the Amazon River in Brazil. All the specimens of T. galeatus and T. coriaceus were infected by one or more parasites, such as Ichthyophthirius multifiliis, Tripartiella tetramerii, Trichodina nobilis, Cosmetocleithrum striatuli, Contracaecum sp., Cystidicoloides sp., Dadaytremoides parauchenipteri and Gorytocephalus spectabilis. Seven species were common to both host fish, and there were 1-5 parasite species per host. In both hosts, trichodinids were dominant. Aggregate dispersion of ectoparasites and endoparasites was observed, with greater aggregation among endoparasites. Only the ectoparasites species showed differences in intensity and/or abundance. However, the parasite communities of the two hosts were taxonomically similar (99%) and characterized by high prevalence and high abundance of ectoparasites, but with low diversity, prevalence and abundance of endoparasites. Trachelyopterus galeatus, the host with the larger body size, presented greater variation of Brillouin diversity and evenness, while T. coriaceus had higher Berger-Parker dominance values and total numbers of parasites. This first study on these parasites of T. galeatus and T. coriaceus showed that the life mode, size of the hosts and the availability of infective forms of the parasites were the main factors that influenced the parasite communities structure.Keywords: Amazon, auchenipterid, diversity, infection, parasites. ResumoO objetivo deste estudo foi comparar as comunidades, prevalência, intensidade, abundância e interações parasito-hospedeiro em duas populações de hospedeiros simpatricos, Trachelyopterus coriaceus e Trachelyopterus galeatus de um tributário do sistema do Rio Amazonas, no Brasil. Todos os espécimes de T. galeatus e T. coriaceus estavam infectados por um ou mais parasitos, tais como Ichthyophthirius multifiliis, Tripartiella tetramerii, Trichodina nobilis, Cosmetocleithrum striatuli, Contracaecum sp., Cystidicoloides sp., Dadaytremoides parauchenipteri e Gorytocephalus spectabilis. Sete espécies de parasitos foram comuns para ambos os peixes hospedeiros e houve de 1-5 espécies de parasitos por hospedeiro. Em ambos os hospedeiros houve dominância de espécies de tricodinídeos. A dispersão dos ectoparasitos e endoparasitos foi agregada, mas a maior agregação foi de endoparasitos. Somente espécies de ectoparasitos mostraram diferenças na intensidade e/ou abundância. Entretanto, as comunidades parasitárias dos dois hospedeiros foram taxonomicamente semelhante (99%) e caracterizada por alta prevalência e abundância de ectoparasitos, mas com baixa diversidade, prevalência e abundância de endoparasitos. Trachelyopterus galeatus, com maior tamanho corporal, apresentou maior variação da diversidade Brillouin e uniformidade, enquanto T. coriaceus teve maiores valores de dominância de Berger-Parker e número total de parasitos. Este primeiro ...

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The present study describes, for the first time, histopathological alterations in the gills of Macrobrachium amazonicum caused by infestation of Probopyrus bithynis (Isopoda: Bopyridae). In every case (100%), the infestation by P. bithynis was by a single pair of parasites (male and female) and occurred in the right or left side of the branchial chamber; the gill structures were visibly compressed due to the presence of parasites. The gills of M. amazonicum parasitized by P. bithynis exhibited a chronic inflammatory response, with the presence of edema, greater quantities of hemocytes, necrosis, epithelial cell hyperplasia, rupture of the pillar cells at the ends of the gill lamellae, desquamation of the cuticle, lamellar fusion and rupture of the lamellar epithelium. Tissue lesions were found in the histological sections of the gills of the parasitized M. amazonicum. Structural alterations in the branchial chamber of the hosts caused by the presence of P. bithynis can lead to physiological changes that can impair host respiratory performance. Finally, histopathological alterations in the branchial chamber of hosts suggest that P. bithynis feed directly on the gill tissues of this shrimp.

This study investigated the acute toxicity (LC50‐24 hr) effects of the essential oil of Cymbopogon citratus for adult Argulus sp. and Dolops discoidalis, before and during oviposition. In vitro acute toxicity (LC50‐24 hr) was tested using 20, 40, 60, 80, 100, 120, 140 and 160 μg/L of C. citratus essential oil, and two control groups (one with cultivation tank water and one with cultivation tank water + alcohol) were used. Specimens of Argulus sp. and D. discoidalis submitted to acute toxicity were evaluated using histological procedures. The major chemical compounds of C. citratus essential oil were geranial (47.5%), neral (35.6%) and myrcene (6.7%). The LC50‐24 hr for Argulus sp. adults was 67.97 μg/L, while for D. discoidalis it was 59.55 µg/L. In the oviposition of both species of argulids, maximum mortality began with treatments of 140 μg/L, while the LC50‐24 hr for Argulus sp. and D. discoidalis was 83.98 μg/L and 82.48 μg/L, respectively. In both argulid species exposed to C. citratus essential oil, morphological alterations were observed only in the eyes, and they occurred in the ommatidium and rhabdomeres and were dependent on the concentration of C. citratus essential oil and the parasite species.