A taxonomic survey of six nematode species (including three new taxa) from the genus Cucullanus Müller, 1777, parasites of marine fishes off the Brazilian coast, is provided. Nematodes were studied using light and scanning electron microscopy (SEM). Cucullanus gastrophysi n. sp. parasitic in Lophius gastrophysus Miranda Ribeiro differs from its congeners by the combination of the following features: shape and number of sclerotized structures in the oesophastome (a pair of lateral elongate structures and a single small reniform one), position of deirids and excretory pore (both anterior to oesophagus base), spicule length and spicule/body length ratio (0.97-1.29 mm and 6.5-10.5%, respectively), morphology and length of gubernaculum (V-shaped, 107-135 µm long). Cucullanus protrudens n. sp. from Pagrus pagrus (Linnaeus) has the cloacal lips broadly protruded, which differentiates it from several species of Cucullanus; other features, e.g., the length of spicules and gubernaculum (400-415 µm and 91-103 µm, respectively), arrangement of caudal papillae and position of excretory pore (slightly posterior to oesophagus-intestine junction) also characterize this species. Cucullanus pseudopercis n. sp. from Pseudopercis semifasciata (Cuvier) has deirids and excretory pore posterior to the oesophagus-intestine junction, which distinguishes the species from most of the congeners; furthermore, the arrangement of caudal papillae in combination with the length of spicules and gubernaculum (1.0-1.5 mm and 178-196 µm, respectively) separate this species from other taxa. Newly collected specimens of C. cirratus Müller, 1777 (type species of the genus) from Urophycis brasiliensis (Kaup), C. pedroi from Conger orbignianus Valenciennes (type host of the species) and C. genypteri Sardella, Navone & Timi, 1997 from Genypterus brasiliensis Regan, were studied as well. Comparisons between newly collected samples and the taxonomic data available for each respective species revealed features that were not previously mentioned (e.g. presence of unpaired cloacal papilla, detailed morphology of cloacal lips), as well as negligible differences in morphometry and caudal papillae arrangement. Observations on the type material of C. carioca suggested affinities with the genus Dichelyne Jägerskiöld, 1902; however, the poor preservation of these specimens does not allow further conclusions. Cucullanus rougetae is considered to be a species inquirenda.

One hundred specimens of Pagrus pagrus were necropsied for parasitological study between January and February 2012. These data were compared with data from 90 specimens that had been examined in the year 2000. The fish were collected from Cabo Frio (21-23 ° S, 41-45 ° W), in the state of Rio de Janeiro, Brazil. In the current study a total of 19 parasite species were collected. Sixteen of these were collected in the samples of both 2012 and 2000, thus totaling 25 parasite species in the two studies. All the results were similar to those of the previous study with regard to: dominance of anisakid nematode larvae; correlation between abundance of parasites and host body size; absence of correlations between the size of parasite infrapopulations and host sex; and scarcity of interspecific associations. The only difference between the studies was in the abundance values for Anisakidae, which could be correlated with the seasonal factor of the collection period, which was concentrated in the summer. This is also the period of the South Atlantic Central Water (SACW) phenomenon, during which there is greater host reproductive activity. Therefore, significant stability of the metazoan community structure of P. pagrus was shown.Keywords: Pagrus pagrus, parasites, community structure, marine fish, temporal stability. ResumoCem exemplares de Pagrus pagrus foram necropsiados entre janeiro e fevereiro de 2012 para estudos parasitológicos. Esses dados foram comparados com dados de 90 espécimes examinados no ano 2000. Os peixes foram coletados em Cabo Frio (21-23 ° S, 41-45 ° W), no Estado do Rio de Janeiro, Brasil. No presente estudo, foram coletados um total de 19 espécies de parasitos, 16 delas foram coletadas em comum nas amostras de 2012 e 2000, dando um total de 25 espécies de parasitos. Todos os resultados foram semelhantes aos do estudo anterior em: dominância das larvas de anisaquídeos; correlação entre a abundância de parasitos e comprimento total do corpo dos hospedeiros; ausência de correlações entre o tamanho das infrapopulações parasitárias e sexo do hospedeiro e a escassez de associações interespecíficas. A única diferença entre os estudos reside nos valores da abundância de nematóides anisaquídeos, o que poderia ser correlacionado com o fator sazonal do período de coleta que foi concentrada no verão, período que coincide com o fenômeno da Água Central do Atlântico Sul (ACAS), no qual o hospedeiro apresenta maior atividade reprodutiva. Portanto, uma significativa estabilidade da estrutura da comunidade de parasitos de P. pagrus foi evidenciada.Palavras-chave: Pagrus pagrus, parasitas, estrutura da comunidade, peixe marinho, estabilidade temporal.

Parasitic copepods of the family Lernaeidae are often found infesting freshwater fishes worldwide. They cause lernaeosis, a disease that can lead to serious pathogenic effects on their fish hosts. The most common lernaeid is the Lernaea cyprinacea, which has been widely introduced through importation of tropical fishes, e.g. cyprinids. In South America, it is one of the most common parasites both in wild and in farmed fish in the central region of Argentina. The silverside Odontesthes bonariensis is the most important fish of the sport fisheries of Argentina and one of the fish most affected by lernaeosis. Six specimens of copepods were collected from 30 specimens of O. bonariensis collected in a Pampean shallow lake (33°25'28"S 62°53'56"W) of Córdoba (Argentina). The 28S rRNA gene of L. cyprinacea was amplified by means of PCR to obtain the 28S rDNA sequence. The sequence obtained of this parasite from Argentina showed high genetic similarity with those from various geographical origins. The present study provided molecular characterization of L. cyprinacea in South America for the first time.

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Metazoan parasite assemblages of Pagrus pagrus inhabiting the southwestern Atlantic were analysed with the aim of identifying the existence of different stocks and to comparatively assess the value of different parasite guilds as indicators of zoogeographical regions. A total of 186 fish was examined. Samples were obtained from three Brazilian and one Argentine localities, distributed in three different biogeographic districts of the Argentine Zoogeographical Province. Pagrus pagrus harboured 26 metazoan parasite species distributed in three guilds, ectoparasites (10 species), long-lived larval endoparasites and short-lived gastrointestinal endoparasites (eight species each). Prevalence and abundance values of the former two guilds allowed analysing them comparatively to assess their value as biological indicators of both host population structure and zoogeography. Results of analyses on long-lived parasites evidenced the existence of three stocks, one in the regions of Rio de Janeiro and Sao Paulo, other in southern Brazil (Rio Grande do Sul) and a third in northern Argentina (Mar del Plata), responding to the differential environmental conditions characteristic of three zoogeographical ecoregions. Ectoparasite assemblages exhibited significant differences between all pairs of samples, including those considered as a single stock according to data on persistent parasites. Assemblages of long-lived larval parasites are considered as better indicators for stock assessment purposes than ectoparasites, whose population parameters were variable temporally and heterogeneous at small spatial scales. The distributional variability of persistent parasites of P. pagrus along large scales provides valuable information to help defining robust biogeographical patterns, applicable to stock identification and fishery management of this species.