The present study is part of an ongoing investigation into the characteristics of Myxozoan parasites of Brazilian freshwater fish and was carried out using morphology, histopathology and electron microscopy analysis. A new Myxosporea species (Henneguya pseudoplatystoma) is described causing an important reduction in gill function in the farmed pintado (a hybrid fish from a cross between Pseudoplatystoma corruscans and Pseudoplatystoma fasciatum), which is a commercially important South American catfish. From a total of 98 pintado juveniles from fish farms in the states of São Paulo and Mato Grosso do Sul (Brazil), 36 samples (36.7%) exhibited infection of the gill filaments. Infection was intense, with several plasmodia occurring on a same gill filament. The plasmodia were white and measured up to 0.5 mm in length; mature spores were ellipsoidal in the frontal view, measuring 33.2 ± 1.9 μm in total length, 10.4 ± 0.6 μm in body length, 3.4 ± 0.4 μm in width and 22.7 ± 1.7 μm in the caudal process. The polar capsules were elongated, measuring 3.3 ± 0.4 μm in length and 1.0 ± 0.1 μm in width and the polar filaments had six to seven turns. Histopathological analysis revealed the parasite in the connective tissue of the gill filaments and lamella. No inflammatory process was observed, but the development of the plasmodia reduced the area of functional epithelium. Ultrastructural analyses revealed a single plasmodial wall, which was in direct contact with the host cells and had numerous projections in direction of the host cells as well as extensive pinocytotic canals. A thick layer (2-6 μm) of fibrous material and numerous mitochondria were found in the ectoplasm. Generative cells and the earliest stage of sporogenesis were seen more internally. Advanced spore developmental stages and mature spores were found in the central portion of the plasmodia. © 2009 Elsevier B.V. All rights reserved.1661-25259Abdel-Ghaffar, F., Abdel-Baki, A., Bayoumy, E.M., Bashtar, A., Qurieshy, S., Morsey, K.S., Alghamdy, A., Mehlhorn, H., Light and electron microscopy study on Henneguya suprabranchiae Landsberg, 1987 (Myxozoa: Myxozporea) infecting Oreochromis niloticus, a new host record (2008) Parasitol. Res., 103, pp. 609-617Adriano, E.A., Arana, S., Cordeiro, N.S., Histopathology and ultrastructure of Henneguya caudalongula n. sp. infecting Prochilodus lineatus (Pisces: Prochilodontidade) cultivated in the state of São Paulo, Brazil (2005) Mem. Inst. Oswaldo Cruz, 100, pp. 177-181Adriano, E.A., Arana, S., Cordeiro, N.S., Histology, ultrastructure and prevalence of Henneguya piaractus (Myxosporea) infecting the gills of Piaractus mesopotamicus (Characidae) cultivated in Brazil (2005) Dis. Aquat. Org., 64, pp. 229-235Adriano, E.A., Arana, S., Cordeiro, N.S., An ultrastructural and histopathological study of Henneguya pellucida n. sp. (Myxosporea: Myxobolidae) infecting Piaractus mesopotamicus (Characidae) cultivated in Brazil (2005) Parasite, 12, pp. 221-227Adriano, E.A., Arana, S., Ceccarelli, P.C., Cordeiro, N.S., Light and scanning electron microscopy of Myxobolus porofilus n. sp. (Myxosporea: Myxobolidae) infecting the visceral cavity of Prochilodus lineatus (Pisces: CharaciformesProchilodontidae) cultivated in Brazil (2002) Folia Parasitol., 49, pp. 259-262Azevedo, C., Casal, G., Matos, P., Matos, E., A new species of Myxozoa, Henneguya rondoni n. sp. (Myxozoa), from the peripheral nervous system of the Amazonian fish, Gymnorhamphichthys rondoni (Teleostei) (2008) J. Eukaryot. Microbiol., 55, pp. 229-234Azevedo, C., Matos, E., Fine structure of Henneguya pilosa sp. n. (Myxozoa: Myxosporea), parasite of Serrasalmus altuvei (Characidae), in Brazil (2003) Folia Parasitol., 50, pp. 37-42Azevedo, C., Matos, E., Fine structure of the myxosporean, Henneguya curimata n. sp., parasite of the Amazonian fish, Curimata inormata (Teleostei, Curimatidae) (2002) J. Eukaryot. Microbiol., 49, pp. 197-200Barassa, B., Adriano, E.A., Arana, S., Cordeiro, N.S., Henneguya curvata n. sp. (Myxosporea: Myxobolidae) parasitising the gills of Serrasalmus spilopleura (Characidae: Serrasalminae), a South American freshwater fish (2003) Folia Parasitol., 50, pp. 151-153Bowser, P.R., Conroy, J.D., Histopathology of gill lesions in channel catfish associated with Henneguya (1985) J. Wild Dis., 21, pp. 177-179Campos, J.L., O cultivo do pintado, Pseudoplatystoma corruscans (Spix e Agassiz, 1829) (2005) Espécies nativas para piscicultura no Brasil, pp. 327-343. , Baldisserotto B., and Gomes L.C. (Eds), Editoraufsm, Santa MariaCasal, G., Matos, E., Azevedo, C., Light and electron microscopic study of the myxosporean, Henneguya friderici n. sp. from the Amazonian teleostean fish, Leporinus friderici (2003) Parasitology, 126, pp. 313-319Casal, G., Matos, E., Azevedo, C., Some ultrastructural spects of Henneguya striolata sp. nov. (Myxozoa: Myxosporea), a parasite of the Amazonian fish Serrasalmus striolatus (1997) Parasitol. Res., 83, pp. 93-95Current, W.L., Janovy Jr., J., Comparative study of ultrastructure of interlamellar and intralamellar types of Henneguya exilis Kudo from channel catfich (1978) J. Protozool., 25, pp. 56-65Duhamel, G.E., Kent, M.L., Dybdal, N.O., Hedrick, R.P., Henneguya exilis Kudo associated with granulomatous branchitis of channel catfish Ictalurus punctatus (Rafinesque) (1986) Vet. Pathol., 23, pp. 354-361Dykova, I., Lom, J., Hostopathological changes in fish gills infected with myxosporidian parasites of the genus Henneguya (1978) J. Fish Biol., 12, pp. 197-202Eiras, J.C., Takemoto, R.M., Pavanelli, G.C., Henneguya corruscans n. sp. (Myxozoa, Myxosporea, Myxobolidae), a parasite of Pseudoplatystoma corruscans (Osteichthyes, Pimelodidae) from the Paraná River, Brazil: a morphological and morphometric study (2009) Vet. Parasitol., 159, pp. 154-158Eiras, J.C., Takemoto, R.M., Pavanelli, G.C., Henneguya caudicula n. sp. (Myxozoa, Myxobolidae) a parasite of Leporinus lacustris (Osteichthyes, Anostomidae) from the High Paraná River, Brazil, with a revision of Henneguya spp. infecting South American fish (2008) Acta Protozool., 47, pp. 149-154Eiras, J.C., Synopsis of the species of the genus Henneguya Thelohan, 1892 (Myxozoa: Myxosporea: Myxobolidae) (2002) Syst. Parasitol., 52, pp. 43-54El-Mansy, A., Bashtar, A.R., Histopathological and ultrastructural studies of Henneguya suprabranchiae Landsberg, 1987 (MyxosporeaMyxobolidae) parasitizing the suprobranchial organ of the freshwater catfish Clarias gariepinus Burchell, 1822 in Egypt (2002) Parasitol. Res., 88, pp. 617-626Feijó, M.M., Arana, S., Ceccarelli, P.S., Adriano, E.A., Light and scanning electron microscopy of Henneguya arapaima n. sp. (Myxozoa: Myxobolidae) and histology of infected sites in pirarucu (Arapaima gigas: Pisces: Arapaimidae) from the Araguaia River, Brazil (2008) Vet. Parasitol., 157, pp. 59-64Feist, S.W., Longshaw, M., Phylum myxozoa (2006) Fish Diseases and Disorders, Vol. 1: Protozoan and Metazoan Infections. second ed., pp. 230-296. , Woo P.T.K. (Ed), CAB International, UKFroese, R., Pauly, D., 2009. FishBase. World Wide Web Electronic Publication. Version (03/2009). www.fishbase.org (Accessed on 25/02/2009)Ibama, (2008) Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renováveis Estatística da pesca 2006 Brasil: Grandes regiões e unidades da federação, , Ibama, Brasília, 174 ppKabsch, W., Vandekerckhove, J., Structure and function of actin (1992) Annu. Rev. Biophys. Biolmol. Struct., 21, pp. 49-76Kalavati, C., Narasimhamurti, C.C., Histopathological changes in the gills of Chamma punctatus Bl. Infected with Henneguya waltairensis (1985) Ach. Protistenkd., 129, pp. 199-202Kpatcha, T.K., Faye, N., Diebakate, C., Fall, M., Toguebaye, B.S., Nouvelles espèces d'Henneguya Thélohan, 1895 (Myxozoa, Myxosporea) parasites des poissons marins du Sénégal: Étude en microscopie photonique et électronique (1997) Ann. Sci. Nat. Zool., 18, pp. 81-91Lundberg, J.G., Littmann, M.W., Family Pimelodidae (long-whiskered catfishes) (2003) Check List of the Freshwater Fishes of South and Central America, pp. 432-446. , Reis R.E., Kullander S.O., and Ferraris Jr. C.J. (Eds), Edipucrs, Porto AlegreMar and Terra, (2009) A grife do Peixe, , http://www.mareterra.com.br/, Accessed on 25/02/2009Martins, M.L., Onaka, E.M., Henneguya garavelli n. sp. and Myxobolus peculiaris n. sp. (Myxozoa: Curimatidae) in the gills of Cyphocharax nogelli (Osteichthyes: Curimatidae) from Rio do Peixe reservoir, São José do Rio Pardo, São Paulo, Brazil (2006) Vet. Parasitol., 137, pp. 253-261Martins, M.L., Souza, V.N., Moraes, J.R., Moraes, F.R., Gill infection of Leporinus macrocephalus Garavello and Britski, 1988 (Osteichthyes: Anostomidae) by Henneguya leporinicola n. sp. (Myxozoa: Myxobolidae). Description, histopathology and treatment (1999) Rev. Bras. Biol., 59, pp. 527-534Martins, M.L., Souza, V.N., Moraes, J.R.E., Moraes, F.R., Costa, A.J., Pathology and behavioural effects associated with Henneguya sp. (Myxozoa: Myxobolidae) infections of captive pacu Piaractus mesopotamicus in Brazil (1997) J. World Aquat. Soc., 28, pp. 297-300Molnár, K., Székely, C., Mohamed, K., Shaharom-Harrison, F., Myxozoan pathogens in cultured Malaysian fishes. I. Myxozoan infections of the sutchi catfish Pangasius hypophthalmus in freshwater cage cultures (2006) Dis. Aquat. Org., 68, pp. 209-218Molnár, K., Székely, C., Mohamed, K., Shaharom-Harrison, F., Myxozoan pathogens in cultured Malaysian fishes. II. Myxozoan infections of redtail catfish Hemibagrus nemurus in freshwater cage cultures (2006) Dis. Aquat. Org., 68, pp. 219-226Molnár, K., Taxonomic problems, seasonality and histopathology of Henneguya creplini (Myxosporea) infection of the pikeperch Stizostedion lucioperca in Lake Balaton (1998) Folia Parasitol., 45, pp. 261-269Morris, D.J., Adams, A., Sacculogenesis and sporogony of Tetracapsuloides bryosalmonae (Myxozoa: Malacosporea) within the bryozoan host Fredericella sultana (Bryozoa: Phylactolaemata) (2007) Parasitol. Res., 100, pp. 983-992Noga, E.J., (2000) Fish Disease: Diagnosis and Treatment, , Blackwell Publishing Company, USA pp. 173-178Rocha, E., Matos, E., Azevedo, C., Henneguya amzonica n. sp. (Myxozoa, Myxobolidae), parasitizing the gills of Crenicichla lepidota Heckel, 1840 (Teleostei, Cichlidae) from Amazon River (1992) Eur. J. Prostistol., 28, pp. 273-278Schmahl, G., Mehlhorn, H., Taraschewski, H., Treatment of fish-parasites. 7. Effects of sym. triazinone (Toltrazuril) on developmental stages of Myxobolus sp. Bütschli, 1882 (Myxosporea, Myxozoa): a light and electron microscopic study (1989) Eur. J. Protistol., 25, pp. 26-32Work, T., Takata, G., Whipps, C., Kent, M., Henneguya akule n. sp. in the big eyed scad (Selar crumenophthalmus) from Hawaii (2008) J. Parasitol., 94, pp. 524-529Yokoyama, H., Kawakami, H., Yasuda, H., Tanaka, S., Henneguya lateolabracis sp. n. (Myxozoa: Myxosporea) the causative agent of cardiac henneguyosis in Chinese sea bass Lateolabrax sp. (2003) Fish. Sci., 69, pp. 1116-1120