Summary :The characteristics of Myxobolus cuneus n. sp. and its relationship to the host Piaractus mesopotamicus are described based on light and electron microscopy and histological observations. Polysporic plasmodia measuring 20 µm to 2.1 mm in size were found in 63.3 % of the P. mesopotamicus examined. The parasite was found in the gall bladder, urinary bladder, gills, spleen, fins, head surface, liver and heart. Generative cells and disporoblastic pansporoblasts occurred along the periphery of the plasmodia, and mature spores were found in the internal region. The mature spores had a pear shaped body in frontal view, with a total length of 10.0 ± 0.6 µm and a width of 5.1 ± 0.3 µm (mean ± SD). The spore wall was smooth with sutural folds. The polar capsules were elongated, were pear shaped, and equal in size (length 5.7 ± 03 µm; width 1.7 ± 0.2 µm), with the anterior ends close to each other. The polar filaments were tightly coiled in 8-9 turns perpendicular to the axis of the capsule. The plasmodia were always found in connective tissue (wall of the arterioles of the gill filaments, serous capsule of the gall bladder, middle layer and subepithelial connective tissue of the urinary bladder, connective tissue between the rays of the fins, subcutaneous tissue of the head surface and fibrous capsule spleen). The parasite caused important damage in the gills, where development occurred in the wall of gill filament arterioles; a mild macrophage infiltrate was also observed. In advanced developmental stages, the plasmodia caused deformation of the arteriole structure, with a reduction and, in some cases, obstruction of the lumen. The parasite was found throughout the period studied and its prevalence was unaffected by host size, season or water properties. 'hôte, ni par l'environnement (saison, propriétés de l'eau). Résumé : MYXOBOLUS CUNEUS

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The histopathological and ultrastructural characteristics of Henneguya piaractus, a parasite of the gill lamellae of Piaractus mesopotamicus, are reported here. Histological analysis showed that the plasmodia were of the intralamellar type. The development of the plasmodia resulted in marked dilatation of the infected lamellae, with the neighbouring lamellae being displaced laterally. Discreet epithelial hyperplasia was observed, but there was no inflammatory reaction. Ultrastructural analysis showed that the plasmodium had a single thin wall that was in direct contact with the host cells. Pinocytic canals and points of phagocytosis were observed in the wall. The prevalence of the parasite varied according to host size, with the lowest prevalence occurring in hosts up to 10 cm long.

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Abstract. Myxobolus porofilus sp. n. is described infecting the visceral cavity of Prochilodus lineatus (Valenciennes, 1836) cultivated in São Paulo State, Brazil. The plasmodial form of the parasite is 3-5 mm in length and appeared compressed between the wall of the visceral cavity and the pyloric caecum, reposing on this organ. The spores are small (length 5.7 ± 0.3 µm, width 4.8 ± 0.2 µm; mean ± SD) and round to elliptical in frontal view. The valve surfaces are smooth and have sutural folds. The polar capsules are ovoid, small (length 1.6 ± 0

Prochilodus lineatus (Valenciennes, 1836) is a detritivorous teleost popularly known as curimba or curimbatá, is widely distributed in South American rivers and attains a relatively large size, with some specimens measuring 75 cm in length and weighing 8.2 kg (Godoy 1975). It has a high reproductive capacity, rapid growth, good acceptance on the market and is one of the most consumed fish species in Brazil. Its consumption has led to increased interest in its cultivation in fish farms throughout the country.Until recently, Myxobolus porofilus Adriano, Aranas, Ceccarelli et Cordeiro, 2002 was the only myxosporean species reported to parasitize P. lineatus. However, during a survey of myxosporean parasites of fish species cultivated in Brazil, we found a new species of Henneguya parasitizing the gills of P. lineatus. This species is described based on light microscopy, scanning electron microscopy, transmission electron microscopy, and on the histopathological effects produced in the host. MATERIALS AND METHODSFour-month old specimens of P. lineatus (curimbatá), Piaractus mesopotamicus (Holmberg, 1887) (pacu), Brycon cephalus (Günther, 1869) (matrinxã) and Leporinus macrocephalus Garavello et Britski, 1988 (piauçu) obtained from artificial reproduction programs were released in a pond at the Center for the Research and Management of Continental Fishing Resources (Cepta/Ibama) located in the municipality of Pirassununga, state of São Paulo, Brazil. Each month, five specimens of each fish species were examined for the presence of myxozoan parasites from March 2000 to February 2002. Immediately after collection, the fish were transported alive to the laboratory where they were killed by transection of the spinal cord, before being measured and necropsied. Of 120 curimbatá examined, 20 were 7-15 cm long, 78 were 15.1-25 cm long and 22 were 25.1-30.5 cm long.The parasite was identified according to Lom and Arthur (1989). Measurements from 40 fresh mature spores were obtained using a ocular micrometer and are givem in micrometres (mm) as the mean ± standard deviation (SD). Smears containing free spores were stained with a Giemsa solution and mounted in low-viscosity mounting medium (Cytoseal) as permanent preparations. For histological analysis, the gills were fixed in 10% buffered formalin for 24 h, embedded in paraffin, cut into sections 4 µm thick and stained with sirius red (Adriano et al. 2002), haematoxylin and eosin, and PAS. For scanning electron microscopy, free spores were deposited on a coverslip coated with poly-L-lysine and fixed for 2 h at room temperature with glutaraldehyde in 0.1 M sodium cacodylate buffer (pH 7.2). After washing in the same buffer, the preparations were dehydrated in ethanol, critical point dried by CO 2 , coated with metallic gold and examined in JEOL JSM 35 microscope operated at 15 kV. For transmission electron microscopy, fragments of gills containing plasmodia were fixed in 2.5% glutaraldeyde in cacodylate buffer (2 h), dehydrated in increasing concentrations of acetone and embe...

Summary :During a study of myxosporean parasites of cultivated freshwater fish, a new myxosporean species, Henneguya pellucida n. sp., was discovered. Of the 120 Piaractus mesopotamicus sampled, only 10 specimens (8.3 %) were infected. Yellow, round plasmodia measuring 0.5-3 mm were found in the serous membrane of the visceral cavity and in the tunica externa of the swim bladder. Sporogenesis was asynchronous, with the earliest developmental stages aligned prevailingly along the endoplasmic periphery and mature spores in the central zone. The mature spores were pear shaped (total length: 33.3 ± 1.5 µm, mean ± SD; width: 4.1 ± 0.4 µm; body length: 11.4 ± 0.3 µm; caudal process length: 24.1 ± 1.5 µm). The polar capsules were elongated (length: 4.0 ± 0.4 µm; width: 1.6 ± 0.2 µm). The development of the parasite in the swim bladder produced thickening of the tunica externa and a granulomatous reaction. There was no correlation between the prevalence of the parasite and the chemical and physical characteristics of the water. Infection was recorded only in juvenile specimens ranging in size from 9.5 to 20 cm. (longueur totale : 33,3 ± 1,5 µm, moyenne ± SD ; largeur : 4,1 ± 0,4 µm ; longueur du corps : 11,4 ± 0,3 µm ; longueur du processus caudal : 24 1 ± 1,5 µm Résumé

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