Comparative evaluation of the susceptibility of cultivated fishes to the natural infection with myxosporean parasites and tissue changes in the host

Abstract

The purpose of the study was to evaluate the susceptibility of 4 important cultivated fishes to sporozoan parasites. Fishes were collected bimonthly from a pond for a period of 1 year. Myxobolus colossomatis and Henneguya piaractus were found in the internal organs and gills, respectively. The combined incidence of parasitism by both myxozoa was 97.3% in pacu (Piaractus mesopotamicus), 33.3% in hybrid tambacu (Piaractus mesopotamicus x Colossoma macropomum), 5.6% in tambaqui (Colossoma macropomum) and 0% in carp (Cyprinus carpio). Pacu was the most susceptible fish and was parasitized 79.2% in the gills, 66.7% in the kidney and 50% in the spleen. Histopathological evaluation of the gills showed hemorrhages, inflammatory reaction with mononuclear cells and fibroblasts and hyperplasia of basal and goblet cells.Key words: Myxozoa, susceptibility, histopathology, cultivated fish. RESUMO

Myxosporidiosis in intensively-reared Piaractus mesopotamicus: Histopathological diagnosis by means of Ziehl-Neelsen staining

“…However, poor water quality due to excesses of particulate material and/or pollutants also causes subepithelial edema, and this edema protects the integrity of the sinusoid capillaries in that it keeps them further away from the aggressive agent. The consequence of the edema is similar to that of hyperplasia, as previously observed in Piaractus mesopotamicus (Martins et al 1997(Martins et al , 1999a and in Astyanax altiparanae (Barassa et al 2003). …”

“…This cell proliferation occurred in the gill-coating epithelium, between the secondary lamellae, and ϐilled the interlamellar space, thereby promoting fusion and impairing gas and ion exchanges (Martins et al 1997(Martins et al , 1999a. The edema may also have resulted from the presence of the plasmodia, particularly if the plasmodia were located in the lumina of vessels,which would cause blood ϐlow obstruction and increased hydrostatic pressure, and would promote emptying of ϐluid accumulations from the subepithelial space.…”

“…Chronic infection due to myxosporidians may give rise to severe lesions such as necrosis (Molnár & Kovács--Gayer 1985, Dycová & Lom 1988). According to Martins et al (1999a), the presence of Myxobolus sp. may cause damage depending on the host response capacity and/or the virulence of the parasite involved.…”

“…Among the myxosporidians that cause most harm to teleost ϐish reared in captivity in Brazil are the genera Henneguya and Myxobolus (Martins et al 1997, 2000, Martins et al 1999a,b, Moraes & Martins 2004, Schalch & Moraes 2005. Currently, these parasites are identiϐied under the microscope by means of Giemsa staining (Meyers et al 1977) and with Lugol's solution and May-Grünwald-Giemsa staining for observations on fresh specimens; while for histopathological examination, hematoxylin-eosin staining is used.…”

A new species of Henneguya, a gill parasite of Astyanax altiparanae (Pisces: Characidae) from Brazil, with comments on histopathology and seasonality

“…The importance of this genus as a pathogen of freshwater fish has been described by several authors (Dyková & Lom 1978, Kalavati & Narasimhamurti 1985, Lom & Dyková 1995, Martins & Souza 1997, Martins et al 1999a. Among freshwater fish, the genus Astyanax Baird & Girard, 1854 contains approximately 100 species and subspecies that are widely distributed throughout South and Central America (Garutti & Britski 1997).…”