Mem Inst Oswaldo Cruz, Rio de Janeiro, 98(6) September 2003
A New Species of Henneguya, a Gill Parasite of Astyanax altiparanae (Pisces: Characidae) from Brazil, with Comments on Histopathology and Seasonality
Departamento de Parasitologia
*Departamento de Histologia e Embriologia, Instituto de Biologia, Universidade Estadual de Campinas, Caixa Postal 6109, 13083-970 Campinas, SP, Brasil
A new species of Myxosporea,u00a0Henneguya chydadea, is described parasitizing the gills ofu00a0Astyanax altiparanae collected from a lake on Rio das Pedras farm near Campinas, state of São Paulo, Brazil. Of the fish examined, 88.3% had gills parasitized by myxosporeans. The prevalence of the parasite ranged from 80% in the spring and fall, 93% in the summer and 100% in the winter. The parasite induced the formation of white, oval-shaped cysts measuring 40-64 u00b5m x 64-80 u00b5m which deformed the gill lamellae, compressed the capillaries, and caused retraction of the neighboring lamellae. The mature spores were elongated and had two identical, parallel elongate polar capsules. Each capsule contained a polar filament with 9-10 turns. There was no mucous envelope or iodinophilous vacuole. Morphometric differences between this parasite and other species of the genusu00a0Henneguyau00a0indicated, that he parasite observed inu00a0A. altiparanaeu00a0is a new species. This is the first report of a myxosporeanu00a0parasitizingu00a0A. altiparanae.
The fish fauna of the neotropical region is the most diversified of the world, and represent about 24% of the global marine and freshwater fish species (Schaefer 1998). With the growth of aquiculture in several regions of the world since 1990 (Kentet al.2001), the study of fish pathologies has become increasingly important. Among agents responsible for diseases in fish are the myxo-sporeans, which cause serious damage to economically important fish species. There are approximately 1 350 species of myxosporeans distributed in 52 genera, most of which parasitize freshwater fish (Kent et al. 2001).
Among myxosporeans, the genus Henneguya Thélohan, 1892 is the most abundant in South America, with 29 known species. 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). These small size fish, popularly known as lambari in Brazil, occupy a fundamental position in the food chain of aquatic ecosystems, were they serve as food for several predators (Esteves 1996). In addition to their commercial value as a source of food in several regions, lambari are also much appreciated for sport fishing (Barbieri & Marins 1995).
The presence of myxosporeans in lambari has been reported, with eight species of Henneguya having been described so far (Cordeiro et al. 1983, Gióia et al.1986, Gióia & Cordeiro 1987), although none in A. altiparanae Garutti & Britski, 2000.
During a study of the myxosporean fauna in A. altiparanae collected near the city of Campinas, in the state of São Paulo, Brazil, we observed a new species of Henneguya parasitizing the gills of this species. In this paper, we describe this new species, and report the prevalence and histopathological modifications caused by this parasite.
MATERIALS AND METHODS
Ten juvenile and adult specimens of A. altiparanae were collected monthly from January to December, 2001 from a lake located on Rio das Pedras farm, close to the city of Campinas and examined for the presence of myxosporeans. The fish were transported alive to the laboratory where they were killed, measured and necropsied. Twenty spores from freshly prepared material obtained from different fish specimens were measured immediately (Lom & Arthur 1989) using a micrometer incorporated into a microscope. The spores were treated with Lugol solution to determine the presence of iodinophilous vacuoles in the sporoplasma, and with India ink to detect the presence of a mucous envelope (Lom & Vávra 1963). Rubbings containing free spores were fixed in methanol, stained with Giemsa solution (pH 7.2) and mounted in Cytosealä. For histopathological analysis, fragments of gill containing cysts obtained from the same specimens of A. altiparanae, were fixed in buffered 10% formalin for 24 h and included in paraffin. Sections 4 µm thick were stained with hematoxylin-eosin. For scanning electron microscopy (SEM), free spores were placed on a slide coated with poly-L-lysine then fixed in glu-taraldehyde, and washed with 1 M sodium cacodylate buffer before dehydration in an alcohol series. After critical point drying, the samples were coated with gold and examined with a JEOL JMS-5900LV electron microscope operated at 15 kV.
The chemical and physical properties of the lake water (pH, conductivity, dissolved solids, and oxygen) were determined monthly using a Corning Check Mate Model 90 meter.
Pearson's correlation coefficient was used to determine whether there was a correlation between the prevalence of the parasite and the properties of the water. A chi-square test was used to compare the seasonal prevalence of the parasite.
Of the 120 (117 adult and 3 juvenile) specimens of A. altiparanae examined, 106 (88.3%) had gills parasitized by myxosporeans. Of the fish parasitized, 97.2% were adult, and 2.8% were juveniles. The overall prevalence of the parasite in males and females was 77.8%, and 90.2%, respectively. The prevalence of the parasites ranged from 80% in the spring and fall, 93% in the summer, and 100% in the winter. This differences was not significant (c2 = 1.01; p = 0.05). In the spring, the prevalence of infected adult and juveniles was 79.3% (23/29) and 100% (1/1) respectively, whereas in the summer, the corresponding values were 92.8% (26/28) and 100% (2/2). In the fall and winter, the prevalence of infected adult was 80% (24/30) and 100% (30/30) respectively. No juveniles were collected in these two seasons. There was no significant correlation between the prevalence of parasites and the chemical and physical properties of the water, including pH (r = 0.25; p = 0.42), conductivity (r = 0.39; p = 0.19), dissolved oxygen (r = -0.11; p = 0.73), dissolved solids (r = 0.29; p = 0.34) and temperature (r = -0.35; p = 0.26). Based on the shape and dimensions of the spores, the myxosporean studied was identified as a new species of Henneguya.
Vegetative stage - White, oval-shaped and polysporic cysts measuring 40-64 µm x 64-80µm were encountered in the gill lamellae of A. altiparanae. When opened, spores in all stages of development were observed (Fig. 1A).
Spores (n = 20) - Mature spores elongated (total length 17.6-20 µm; spore length 8.8-11.2 µm; spore width 3.2-5.6 µm; thickness 3.6-4 µm; caudal appendix length 8-9.6 µm). Sporoplasma binucleate. Two polar capsules elongated and of equal size (length 3.2-4.4 µm, width 1.2- 1.6 µm). Polar filament with 9-10 coils, arranged perpendicular to the axis of the capsule. Spore wall smooth consisting of two symmetrical valves with a visible line of suture (Figs 2, 3). Scanning electron microscopy revealed two pores for the discharge of polar filaments situated at the anterior extremity of the spore on one side of the line of suture (Fig. 2B). Mucous envelope or iodinophilous vacuole not seen.
Type host - Astyanax altiparanae Garutti & Britski, 2000 (Characidae: Tetragonopterinae)
Site of infection - Gill lamella epithelium
Prevalence - 88.3% (106/120)
Locality - Rio das Pedras farm, municipality of Campinas, state of São Paulo, Brazil.
Type material - slides with stained spores of H. chydadea sp. n. (Syntipe) were deposited in the collection of the Museum of Natural History in the Institute of Biology, State University of Campinas (Unicamp) (accession numbers ZUEC 10 and 11).
Etymology - the specific name of the parasite is derived of the Latin word chydaeus (= common).
Histopathology - Histological analysis of the gills of A. altiparanae revealed that the H. chydadea cysts wereof the intralamellar-type located in the gill lamella epithelium. The initial development of the cysts occurred in several regions (basal, median and distal) of the gill lamella without compromising the gill structure (Fig. 1B, C). In more advanced stages, the cysts occupied the entire lamella and caused its deformation. As a result, the epithelial cells were compressed and their nucleus were situated to the free surface. Compression of the capillaries and retraction of the neighboring lamellae were also observed (Fig. 1D). No inflammatory reaction or hyperplasia was observed during development of the cysts.
The shape and dimensions of the cysts and spores of H. chydadea were compared with those of other species ofHenneguya reported for freshwater fish of South America and other parts of the world. Of the species described, onlyH. wenyoni Pinto, 1928, which parasitizes the gills of Tetragonopterus sp. (Pinto 1928), and H. santae Guimarães & Bergamini, 1934, which parasitizes the gills of Tetragonopterus santae (Gimarães & Bergamini 1934), shared some features with H. chydadea (Table). The spores of H. wenyoni resembled those of H. chydadea in body length and in the length and width of the polar capsules. However, the spores of H. wenyoni had a longer tail process and the body was wider.The morphology and body width of the spores of H. santae weresimilar to those of H. chydadea, but the tail process of H. santae was longer and the body and polar capsule lengths were shorter than in H. chydadea. In addition, the spores of H. wenyoni and H. santae had an iodinophilous vacuole and the polar capsules were of variable size, whereas in H. chydadea the iodinophilous vacuole was absent and the polar capsule dimensions were constant. The dimensions of the cysts in H. wenyoni (2 mm x 1 mm)and H. santae (1 mm x 0.70 mm) were greater than those of H. chydadea cysts(40-64 µm x 64-80 µm). Based on the morphometric differences, the parasite observed in A. altiparanae was considered to be a new species of Henneguya, and the first to be recorded in A. altiparanae.
No significant seasonal differences were found, therefore the number of mature H. chydadea cysts and spores in the gills of A. altiparanae was greatest during the winter, and gradually decreased thereafter, probably through rupture. These observations suggest that H. chydadea coud have a seasonalcycle of development in A. altiparanae, although further studies are needed to confirm this. The properties of the lake water had no effect on the prevalence of the parasite throughout the year.
A seasonal reproductive cycle has also been reported for other species of Henneguya. Molnár (1998) observed seasonality and synchronicity in the development of the cysts and spores of H. creplini, a parasite of the gills ofStizostendion lucioperca. The young cysts of H. creplini appeared in the gills of S. lucioperca in April and gradually grew to form spores in the winter. Rupture of the cysts to release the spores occurred in March of the following year. Cone (1994) reported that for H. doori, a parasite of Perca flavescens, cyst development and spore release occurred between September of one year and March of the following year. This author also observed that rupture of the cysts and the release of spores occurred following an increase in temperature.
The development of H. chydadea cysts in the epithelium of the gill lamellae of A. altiparanae resulted in deformation of the lamellae and compression of the capillaries. In more advanced stages, when the cysts occupied the entire length of a lamella, retraction of the neighboring lamellae was observed, with a reduction in the surface available for gas exchange. In the initial stages, cysts development occurred on one side of the gill lamella, with marked dilatation of the side infected. According to Molnár (2002), such cysts are classified as asymmetric.
In a similar histopathological study of the gills of S. lucioperca parasitized by H. creplini, which produce the same kind of cysts, as those described here, Molnár (1998) also reported hyperplasia and the formation of a thick layer of granular tissue.
In other works, Kalavati and Narasimhamurti (1985), who studied Channa punctatus infected by H. waltairensis,Martins and Souza (1997), who studied the gills of Piaractus mesopotamicus parasitized by Henneguya sp., and Martins et al.(1999b), who studied the gills of Leporinus macrocephalus infected by H. leporinocola, hemorrhage and/or inflammatory foci were observed, neither of which was seen here.
Although massive infection by H. chydadea was not observed, the histopathological alterations (deformation of the structures, compression of the capillaries and retraction of the neighboring lamellae) indicated that this parasite is potentially pathogenic, and that a high parasite load could compromise gill functions.
To the Laboratório de Microscopia Eletrônica, Laboratório Nacional de Luz Síncrotron, Campinas, Brazil, for use of the electron microscope. To Nilson Branco for help in the field work and Dr Stephen Hyslop for editing the English.
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