Thunnus atlanticus is of great commercial importance in Brazil, but infections caused by helminth parasites can reduce its commercial value. In this paper, 15 species of Digenea and three of Monogenoidea were recovered from 61 specimens of T. atlanticus collected from the coastal zone of the State of Rio de Janeiro. Species of the family Didymozoidae were the dominant species, with highest prevalence and abundance values. The parasites showed the typical aggregated distribution pattern, except for Nasicola brasiliensis, which had an aleatory distribution pattern. Prevalence and abundance of Didymosulcus philobranchiarca, Didymocystis lamotheargumedoi and Didymosulcus wedli and prevalence of Koellikerioides internogastricus were positively correlated with the total length of the host. The abundance of Coeliotrema thynni was negatively correlated with total length of the host. New hosts re...

Four species of scombrid fishes (Perciformes) from the coastal zone of Rio de Janeiro, Brazil, wereexamined for helminth parasites. These are Thunnus albacares (Bonnaterre, 1788), Thunnus atlanticus(Lesson, 1831), Thunnus obesus (Lowe, 1839) and Euthynnus alletteratus (Rafinesque, 1810). Threespecies of the genus Koellikerioides Yamaguti, 1970: K. apicalis Yamaguti, 1970, K. externogastricusYamaguti, 1970 and K. intestinalis Yamaguti, 1970, were recorded from the gill raker, the outer musclelayer of the stomach wall and the inner surface of the small intestine, respectively. Originalmeasurements, parameters of infection and original figures are presented. K. apicalis and K. intestinalisshowed the typical aggregated distribution pattern. Statistical analysis showed that there was asignificant negative correlation between the total lengths of E. alletteratus and the prevalence of K.intesti...

A new species of Rhinoxenoides was described parasitizing the gill filaments of neotropical triportheid fishes. The new species was described from Triportheus angulatus (Spix & Agassiz, 1829) from the Juruá River, State of Acre, Brazil. Rhinoxenoides cruzeirensis n. sp. resembles Rhinoxenoides horacioschneideri Santos Neto, Costa, Soares & Domingues, 2018, mainly by presenting a coiled male copulatory organ (MCO) with clockwise rings; accessory piece with articulation process extending within the coils to the base of MCO; dorsal anchor with well-developed superficial root, and dorsal bar absent. However, it differs from this by number of the coils of the MCO; accessory piece formed by a straight piece that expands in the middle, where it folds over itself; ventral bar short and robust; dorsal anchor with a well-developed superficial root twice as long as the deep root, with a sm...

Parasites are important components of global biodiversity and among them, the Monogenoidea stands out, as parasites of fishes, commonly affecting the gills of their hosts. The aim of the present study was to analyze the presence of species of Urocleidoides parasitizing characiform fishes from the Tocantins River. During the study, specimens of Psectrogaster amazonica Eigenmann & Eigenmann and Caenotropus labyrinthicus (Kner) were collected from the urban zone of the municipality of Imperatriz, state of Maranhão. The gills of the fishes were removed and placed in vials containing hot water (65°C), and posteriorly, absolute ethanol was added to reach a concentration of 70%. A new species of Urocleidoides was described parasitizing both hosts. Urocleidoides psectrogasteri n. sp. can be distinguished by its congeners species principally by the morphology of the MCO.  Besides, the know...

Anacanthorus Mizelle & Price, 1965 is the most diverse genus of Dactylogyridae and is characterized by the absence of anchors and bars in the haptor. Members of Anacanthorus are found parasitizing until now only fishes belonging to order Characiformes. Specimens of Brycon pesu Müller & Troschel, 1845 and Caenotropus labyrinthicus (Kner, 1858) were collected from Tocantins River, Brazil and had their gills removed and individualized in bottles containing water heated to (~65ºC), to relax and release the parasites, and ethanol absolute was increased to reach the concentration of 70%. The parasites found were collected and mounted in Hoyer´s medium. A new species of Anacanthorus, A. itaueirasensis sp. nov., is described from Brycon pesu, presenting the characteristics of Anacanthorus species parasitic on bryconids, as morphology of the copulatory complex, composed of a tubular MC...