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Diplectanid monogeneans are gill parasites that can infect fish in huge numbers and thus become harmful, especially in maricultured fish. It is therefore useful to have taxonomic tools, such as keys, to identify species. The following diplectanid species from groupers of the Mediterranean Sea were studied: five species of Pseudorhabdosynochus Yamaguti, 1958, including P. riouxi (Oliver, 1986) Kritsky & Beverley-Burton, 1986 from the dusky grouper Mycteroperca marginata, P. enitsuji Neifar & Euzet, 2007, P. bouaini Neifar & Euzet, 2007, P. dolicocolpos Neifar & Euzet, 2007 and P. sinediscus Neifar & Euzet, 2007 from the goldblotch grouper M. costae, and Echinoplectanum echinophallus (Euzet & Oliver, 1965) Justine & Euzet, 2006 from the dusky grouper. New material was obtained from fish collected from off Tunisia and Libya and compared to the type-material and voucher specimens in museum collections. Identifications of fish were confirmed by barcoding of cytochrome c oxidase subunit I (COI) sequences. The sclerotized vagina was considered the most important structure for systematics. The three species P. riouxi, P. bouaini, and P. enitsuji share a common general structure of the sclerotized vagina with a conspicuous spherical secondary chamber. We thus propose the 'Pseudorhabdosynochus riouxi group' to accommodate them. Pseudorhabdosynochus dolicocolpos has an elongate vaginal structure that is completely different from all its congeneric species reported from the Mediterranean Sea, and Pseudorhabdosynochus sinediscus has a sclerotized vagina in which the secondary chamber is not visible, and a haptor without squamodiscs. A taxonomic key to diplectanid species on Mycteroperca spp. in the Mediterranean Sea is proposed; it includes ten species of Pseudorhabdosynochus and one species of Echinoplectanum.

Pseudorhabdosynochus suratthaniensis n. sp. is described from the gills of Cephalopholis argus ; P. cephalopholi n. sp., from the gills of C. sonnerati ; and P. samaesarnensis n. sp., from the gills of Epinephelus lanceolatus . These fish were all caught in the Gulf of Thailand. Pseudorhabdosynochus suratthaniensis n. sp. is distinguished from congeneric species by the structure of its sclerotized vagina, which has a wide sclerotized trumpet and a single large primary chamber, and by the number of rows of rodlets in each of its squamodiscs. Pseudorhabdosynochus cephalopholi n. sp. is also distinguished by the structure of its sclerotized vagina that, like the P. suratthaniensis n. sp., has a sclerotized trumpet, but it also has a long coiled or curved primary canal near its midlength, and a distal part with a primary chamber and a secondary chamber communicating with the primary chamber through a short secondary canal. In addition, P. cephalopholi n. sp. is distinguished by some sclerotized organs (ventral and dorsal hamuli, ventral bar, and quadriloculate organ) with different lengths, and by the number of rows of rodlets in each of its squamodiscs. Pseudorhabdosynochus samaesarnensis n. sp. is distinguished by its sclerotized vagina that has an anterior cup-shaped trumpet and a short straight or curved primary canal. For Thailand, these are the first species of Pseudorhabdosynochus described from species of Cephalopholis and the second species of Pseudorhabdosynochus described from Epinephelus . Pseudorhabdosynochus suratthaniensis n. sp. est décrit à partir des branchies de Cephalopholis argus , P. cephalopholi n. sp. des branchies de C. sonnerati , et P. samaesarnensis n. sp. des branchies d’ Epinephelus lanceolatus . Ces poissons ont tous été pêchés dans le golfe de Thaïlande. Pseudorhabdosynochus suratthaniensis n. sp. se distingue des espèces congénères par la structure de son vagin sclérifié, qui possède une large trompette sclérifiée et une seule grande chambre primaire, et par le nombre des rangées de bâtonnets dans chacun de ses squamodisques. Pseudorhabdosynochus cephalopholi n. sp. se distingue également par la structure de son vagin sclérifié qui, comme P. suratthaniensis n. sp., a une trompette sclérifiée, mais a également un long canal primaire enroulé ou incurvé près de sa mi-longueur et une partie distale avec une chambre primaire et une chambre secondaire communiquant avec la chambre primaire par un court canal secondaire. De plus, P. cephalopholi n. sp. se distingue par certains organes sclérifiés (hamuli ventraux et dorsaux, barre ventrale et organe quadriloculé) de longueurs différentes, et par le nombre des rangées de bâtonnets dans chacun de ses squamodisques. Pseudorhabdosynochus samaesarnensis n. sp. se distingue par son vagin sclérifié qui a une trompette antérieure en forme de coupe et un court canal primaire droit ou courbe. Pour la Thaïlande, il s’agit de la première espèce de Pseudorhabdosynochus décrite à partir d’espèces de Cephalopholis et de la deuxième espèce de Pseudorhabdosynochus décrite à partir d’ Epinephelus .

Pseudorhabdosynochus Yamaguti, 1958 is a species-rich diplectanid genus, mainly restricted to the gills of groupers (Epinephelidae) and especially abundant in warm seas. Species from the Mediterranean are not fully documented. Two new and two previously known species from the gills of Mycteroperca spp. (M. costae, M. rubra, and M. marginata) in the Mediterranean and Eastern Atlantic Ocean are described here from new material and slides kept in collections. Identifications of newly collected fish were ascertained by barcoding of cytochrome c oxidase subunit I (COI) sequences. Pseudorhabdosynochus beverleyburtonae (Oliver, 1984) Kritsky & Beverley-Burton, 1986 and P. sosia Neifar & Euzet 2007 are redescribed from type-specimens and new specimens collected off Tunisia and Libya from M. marginata and M. costae, respectively. Pseudorhabdosynochus oliveri n. sp., from M. marginata (type-host) off the Mediterranean coast of France (type-locality), is described from specimens found among voucher specimens of P. beverleyburtonae deposited by Guy Oliver in the collection of the Muséum National d'Histoire Naturelle, Paris. Pseudorhabdosynochus oliveri is distinguished by the shape of its sclerotised vagina; it was not found in the other localities investigated. Pseudorhabdosynochus hayet n. sp. is described from M. rubra (type host) off Senegal (type-locality) and Tunisia. Pseudorhabdosynochus hayet is morphologically similar to P. sosia (type-host: M. costae) but was distinguished by differences in measurements of the vagina and male copulatory organ, different host, and divergent COI sequences. The four species (P. beverleyburtonae, P. sosia, P. oliveri, and P. hayet) share common characteristics such as squamodiscs with 2 innermost circular rows of rodlets and a similar general structure of the sclerotised vagina; we propose to group them into a 'beverleyburtonae group' within Pseudorhabdosynochus.

A survey of the gill parasites of Epinephelus costae (Teleostei: Serranidae) was conducted between 2001 and 2005 in the Gulf of Gabès (Tunisia). Five new species of Diplectanidae (Monogenea) were collected, all belonging to Pseudorhabdosynochus Yamaguti, 1958: P. bouaini sp. n., P. dolicocolpos sp. n., P. enitsuji sp. n., P. sinediscus sp. n., and P. sosia sp. n. These five species differ from each other and from all described species of Pseudorhabdosynochus by the morphology and size of their sclerotized vagina. These diplectanids (except P. sinediscus) were also collected from the same host off Dakar in 1981 and 1989. The present paper includes the descriptions and taxonomic considerations of each of these species in addition to an amended diagnosis of Pseudorhabdosynochus. A key to the five new species parasitizing E. costae is provided. These five species are the first diplectanids described from E. costae.

Pseudorhabdosynochus jeanloui n. sp. (Monogenoidea, Diplectanidae) is described from specimens collected from the gills of the Pacific creolefish, Paranthias colonus (Perciformes, Serranidae) from a fish market in Chorrillos, Lima, Peru. The new species is differentiated from other members of the genus by the structure of its sclerotized vagina, which has two spherical chambers of similar diameter. This is the first Pseudorhabdosynochus species described from the Pacific coast of America, the third species of the genus reported from South America and the first described from a member of Paranthias. Pseudorhabdosynochus jeanloui n. sp. (Monogenoidea, Diplectanidae) est décrit de spécimens collectés sur les branchies de la badèche du Pacifique, Paranthias colonus (Perciformes, Serranidae) d’un marché aux poissons de Chorrillos à Lima au Pérou. La nouvelle espèce se différencie des autres membres du genre par la structure de son vagin sclérifié, qui a deux chambres sphériques de diamètre similaire. Ceci est la première espèce de Pseudorhabdosynochus décrits de la côte Pacifique de l’Amérique, la troisième espèce du genre rapportée d’Amérique du Sud, et la première décrite d’une espèce de Paranthias.

Pseudorhabdosynochus kasetsartensis n. sp. is described from the gills of the cloudy grouper Epinephelus erythrurus (Valenciennes) caught in the lower Gulf of Thailand. The new species is distinguished from other species assigned to the genus by the structure of its sclerotised vagina which has a wide and prominent sclerotised trumpet, long, thin, coiled or curved primary canal, short secondary canal, and primary and secondary chambers that are blind extremities of the primary and secondary canals, respectively. This is the first species of Pseudorhabdosynochus Yamaguti, 1958 described from E. erythrurus and the first record of a species of Pseudorhabdosynochus in Thailand.

Cantang grouper (Epinephelus fuscoguttatus lanceolatus) is a type of marine fish resulted from the engineering of grouper hybridization between female tiger grouper (Epinephelus fuscoguttatus) and male kertang grouper (Epinephelus lanceolatus). The aim of this research was to know the occurrence of trematodes infested in Cantang grouper fish (E. fuscoguttatus lanceolatus) at floating net cages, Lamong Bay, Surabaya, Indonesia. The results showed that 100 samples taken from three floating net units, the total prevalence of ectoparasites in Cantang grouper was 38%. There were 4% infested with Benedenia epinepheli, 3% were infested with Neobenedenia girellae and 26% infested with Pseudorhabdosynochus epinepheli. While infestation of 5% was mixed of Benedenia epinepheli and Pseudorhabdosynochus epinepheli.

Seventeen of twenty-three species of groupers collected from the western Atlantic Ocean and adjacent waters were infected with 19 identified species (13 new) of Pseudorhabdosynochus Yamaguti, 1958 (Dactylogyridea, Diplectanidae); specimens of the Spanish flag Gonioplectrus hispanus, coney Cephalopholis fulva, marbled grouper Dermatolepis inermis, mutton hamlet Alphestes afer, and misty grouper Hyporthodus mystacinus were not infected; the yellowmouth grouper Mycteroperca interstitialis and yellowfin grouper Mycteroperca venenosa were infected with unidentified species of Pseudorhabdosynochus; the Atlantic creolefish Paranthias furcifer was infected with an unidentified species of Diplectanidae that could not be accommodated in Pseudorhabdosynochus. The following species of Pseudorhabdosynochus are described or redescribed based entirely or in part on new collections: Pseudorhabdosynochus americanus (Price, 1937) Kritsky & Beverley-Burton, 1986 from Atlantic goliath grouper Epinephelus itajara; Pseudorhabdosynochus yucatanensis Vidal-Martínez, Aguirre-Macedo & Mendoza-Franco, 1997 and Pseudorhabdosynochus justinella n. sp. from red grouper Epinephelus morio; Pseudorhabdosynochus kritskyi Dyer, Williams & Bunkley-Williams, 1995 from gag Mycteroperca microlepis; Pseudorhabdosynochus capurroi Vidal-Martínez & Mendoza-Franco, 1998 from black grouper Mycteroperca bonaci; Pseudorhabdosynochus hyphessometochus n. sp. from Mycteroperca interstitialis; Pseudorhabdosynochus sulamericanus Santos, Buchmann & Gibson, 2000 from snowy grouper Hyporthodus niveatus and Warsaw grouper Hyporthodus nigritus (new host record); Pseudorhabdosynochus firmicoleatus n. sp. from yellowedge grouper Hyporthodus flavolimbatus and snowy grouper H. niveatus; Pseudorhabdosynochus mcmichaeli n. sp., Pseudorhabdosynochus contubernalis n. sp., and Pseudorhabdosynochus vascellum n. sp. from scamp Mycteroperca phenax; Pseudorhabdosynochus meganmarieae n. sp. from graysby Cephalopholis cruentata; Pseudorhabdosynochus beverleyburtonae (Oliver, 1984) Kritsky & Beverley-Burton, 1986 from dusky grouper Mycteroperca marginata; Pseudorhabdosynochus mizellei n. sp. from red hind Epinephelus guttatus; Pseudorhabdosynochus williamsi n. sp. from rock hind Epinephelus adscensionis; Pseudorhabdosynochus bunkleywilliamsae n. sp. from Nassau grouper Epinephelus striatus; Pseudorhabdosynochus mycteropercae n. sp. from tiger grouper Mycteroperca tigris; and Pseudorhabdosynochus tumeovagina n. sp. from speckled hind Epinephelus drummondhayi. Pseudorhabdosynochus woodi n. sp. from red hind Epinephelus guttatus is described based on specimens from the US National Parasite Collection (USNPC). Drawings of the haptoral and copulatory sclerites of the type specimens in the USNPC of Pseudorhabdosynochus monaensis Dyer, Williams & Bunkley-Williams, 1994 from rock hind Epinephelus adscensionis are presented. Finally, a note confirming Pseudorhabdosynochus epinepheli Yamaguti, 1958 rather than its senior synonym Pseudorhabdosynochus epinepheli (Yamaguti, 1938) Kritsky & Beverley-Burton, 1986 as the type species of Pseudorhabdosynochus is provided. Dix-sept des 23 espèces de mérous prélevées dans les eaux de l’océan Atlantique Ouest et adjacentes sont infectées avec 19 espèces identifiées (13 nouvelles) de Pseudorhabdosynochus Yamaguti, 1958 (Dactylogyridea, Diplectanidae) ; les spécimens de Gonioplectrus hispanus, Cephalopholis fulva, Dermatolepis inermis, Alphestes afer et Hyporthodus mystacinus n’étaient pas infectés ; Mycteroperca interstitialis et Mycteroperca venenosa étaient infectés par des espèces non identifiées de Pseudorhabdosynochus ; Paranthias furcifer était infecté par une espèce non identifiée de Diplectanidae qui ne correspond pas à Pseudorhabdosynochus. Les espèces suivantes de Pseudorhabdosynochus sont décrites ou redécrites, sur la base de nouvelles collections en tout ou pour partie : Pseudorhabdosynochus americanus (Price, 1937) Kritsky & Beverley-Burton, 1986, d’Epinephelus itajara ; Pseudorhabdosynochus yucatanensis Vidal-Martínez, Aguirre-Macedo & Mendoza-Franco, 1997 et Pseudorhabdosynochus justinella n. sp., d’Epinephelus morio ; Pseudorhabdosynochus kritskyi Dyer, Williams & Bunkley-Williams, 1995, de Mycteroperca microlepis ; Pseudorhabdosynochus capurroi Vidal-Martínez & Mendoza-Franco, 1998, de Mycteroperca bonaci ; Pseudorhabdosynochus hyphessometochus n. sp. de Mycteroperca interstitialis ; Pseudorhabdosynochus sulamericanus Santos, Buchmann & Gibson, 2000, d’Hyporthodus niveatus et Hyporthodus nigritus (nouvelle mention d’hôte) ; Pseudorhabdosynochus firmicoleatus n. sp., d’Hyporthodus flavolimbatus et H. niveatus ; Pseudorhabdosynochus mcmichaeli n. sp., Pseudorhabdosynochus contubernalis n. sp. et Pseudorhabdosynochus vascellum n. sp., de Mycteroperca phenax ; Pseudorhabdosynochus meganmarieae n. sp., de Cephalopholis cruentata ; Pseudorhabdosynochus beverleyburtonae (Oliver, 1984) Kritsky & Beverley-Burton, 1986, de Mycteroperca marginata ; Pseudorhabdosynochus mizellei n. sp., d’Epinephelus guttatus ; Pseudorhabdosynochus williamsi n. sp., d’Epinephelus adscensionis ; Pseudorhabdosynochus bunkleywilliamsae n. sp., d’Epinephelus striatus ; Pseudorhabdosynochus mycteropercae n. sp., de Mycteroperca tigris ; Pseudorhabdosynochus tumeovagina n. sp., d’Epinephelus drummondhayi. Pseudorhabdosynochus woodi n. sp., d’Epinephelus guttatus, est décrit à partir de spécimens de la collection nationale de parasites des États-Unis (USNPC). Des dessins des sclérites haptoraux et copulatoires des spécimens types de l’USNPC de Pseudorhabdosynochus monaensis Dyer, Williams & Bunkley-Williams, 1994, d’Epinephelus adscensionis, sont présentés. Enfin, une note confirmant Pseudorhabdosynochus epinepheli Yamaguti, 1958 plutôt que son synonyme Pseudorhabdosynochus epinepheli (Yamaguti, 1938) Kritsky & Beverley-Burton, 1986 comme espèce-type de Pseudorhabdosynochus est fournie.

This study aimed at identifying and quantifying the parasites of wild and cultured dusky grouper Epinephelus marginatus. During a year and thereby all four seasons, 20 wild and 20 cultured groupers were examined for the presence of parasites, except in the last season, in which 19 wild and 20 cultured fish were examined, totalling 159 groupers analysed from Ubatuba, southeastern Brazil. Prevalence, mean intensity of infection, mean abundance and mean relative dominance were calculated. Five species of parasites were identified in fish from both origins: Pseudorhabdosynochus beverleyburtonae (Monogenea), Neobenedenia melleni (Monogenea), Pseudempleurosoma sp. (Monogenea), Helicometrina nimia (Digenea) and larvae of Contracaecum sp. (Nematoda). The prevalence of ectoparasites, in most cases, was higher than endoparasites. The most abundant parasite was the monogenea Pseudorhabdosynochus beverleyburtonae in both wild and cultured fish, along all seasons. Neobenedenia melleni was observed in wild and cultured fish in all seasons, with a gradual increase in the number of parasites from the coldest to the hottest seasons, with the highest prevalence and mean intensity in the summer. Helicometrina nimia was found in all seasons in both wild and cultured fish, except for summer, where its presence was detected only in wild fish. Pseudempleurosoma sp. and larvae of Contracaecum sp. showed low prevalence occurring in wild and cultured fish in the autumn and spring, respectively. This study revealed high intensities of potentially pathogenic parasites that could favour disease outbreaks in culture conditions. Este estudo teve como objetivo identificar e quantificar os parasitos da garoupa verdadeira Epinephelus marginatus selvagem e cultivada. Durante um ano, nas quatro estações, 20 garoupas selvagens e 20 cultivadas foram examinadas quanto à presença de parasitos, exceto na última estação, em que foram examinados 19 peixes selvagens e 20 cultivados, totalizando 159 peixes examinados em Ubatuba, Sudeste do Brasil. A prevalência, intensidade média de infecção, abundância média and dominância média relativa foram calculados. Cinco espécies de parasitos foram identificadas nos peixes de ambas as origens: Pseudorhabdosynochus beverleyburtonae (Monogenea), Neobenedenia melleni (Monogenea), Pseudempleurosoma sp. (Monogenea), Helicometrina nimia (Digenea) e larvas de Contracaecum sp. (Nematoda). A prevalência de ectoparasitos foi, na maioria das vezes, maior do que a de endoparasitos. O parasito mais abundante foi o monogenea Pseudorhabdosynochus beverleyburtonae em ambos os peixes selvagens e cultivados, durante todas as estações. Neobenedenia melleni foi observado e, peixes selvagens e cultivados em todas as estações, com aumento gradativo no número de parasitos das estações mais frias para as mais quentes, com as maiores prevalências e intensidades médias no verão. Helicometrina nimia foi encontrado em todas as estações em ambos os peixes selvagens e cultivados, exceto no verão, em que foi observada sua presença apenas em peixes selvagens. Pseudempleurosoma sp. e larvas de Contracaecum sp. apresentaram baixas prevalências, ocorrendo em peixes selvagens e cultivados no outono e na primavera, respectivamente. Este estudo revelou altas intensidades de parasitos potencialmente patogênicos que podem favorecer surtos de doenças em situações de cultivo.

In this paper, seasonal samples of wild versus cultured groupers, Epinephelus spp., from Daya Bay, South China Sea were examined to survey the seasonality of two important species, Pseudorhabdosynochus coioidesis and P. serrani (Monogenea: Diplectanidae), and to analyze the interspecific relationships between these two parasites. Between April 2008 and January 2009, P. coioidesis and P. serrani were found to be parasitic only on E. coioides Hamilton during summer and winter in the natural waters of Daya Bay, exhibiting a high degree of host specificity, whereas they co-occurred and persisted on several species of hosts, such as E. coioides, E. bruneus Block and E. awoara Temminck & Schlegel, in an experimental polyculture pond during several seasons. E. coioides is the main host for both of these two monogenean species. The overall prevalences and mean intensities of these two parasites on polycultured Epinephelus spp. showed the same pattern of seasonal fluctuations, with the maximum values during autumn, except for the overall prevalence of P. serrani, which reached its maximum values during summer and winter and the minimum values during spring and autumn. Prevalence and mean intensity were found to be related to host size. In the wild, medium-sized fishes harboured higher infections, whereas under cultured conditions the small-sized and large-sized fishes were more heavily infected. Simultaneous infections of P. coioidesis and P. serrani were common, and there was a significant positive interspecific correlation between these two parasites.