Trichodina magna Van As and Basson , 1989 ( Ciliophora : Peritrichia ) from cultured Nile tilapia in the state of Santa Catarina ,

Specimens of Trichodina magna Van As and Bassson, 1989 (Ciliophora: Peritrichia) from the Nile tilapia Oreochromis niloticus collected from October 2004 to June 2005 in fish ponds situated in three regions of Santa Catarina State, Brazil are described here. Wet smears of skin and gills were prepared in the field, air dried, impregnated with Klein’s dry silver method and Giemsa’s solution. From a total of 146 examined fish, 36 were parasitized on the skin, 14 in the gills and 33 on the skin and gills, simultaneously. The mean diameter of the body of the specimens of T. magna was 84.3 ± 12.6 μm, adhesive disc 60.7 ± 10.0 μm, denticulate ring, 38.3 ± 7.4 μm, consisting of 26 (23 to 29) denticles. The only distinguishable difference from the original description was the fact that the ray of the denticle is anteriorly directed and does not extend over the y + 1 axis.


Introduction
Trichodinids are commonly found parasitizing marine (Xu et al., 2001) and freshwater fishes (Arthur and Lom, 1984a).Lom (1958) reported on the specific characteristics that have been considered in trichodinids.Since the studies of Lom (1960Lom ( , 1970) ) in the surroundings of Prague, new species of Trichodina Ehrenberg, 1830 have been described in North America (Wellborn, 1967), Cuba and Russia (Arthur and Lom, 1984a, b), South Africa (Basson and Van As, 1991), Japan (Imai et al., 1991), India (Asmat and Haldar, 1998), Germany (Dobberstein and Palm, 2000), Egypt (Al-Rasheid et al., 2000), China and Korea (Xu et al., 2001).In pond-reared fishes, they have been found on catfish (Basson and Van As, 1991), on perch, and on roach (Halmetoja et al., 1992), in tilapia (Van As and Basson, 1992), in carp (Nikolic and Simonovic, 1998), in eel (Madsen et al. (2000), and in marine cultivated fishes in Korea (Xu et al., 2001).In Brazil, Vargas et al. (2000) and Tavares-Dias et al. (2001) have reported their presence in several cultured freshwater fishes.However, under inadequate conditions of handling, these ciliates may proliferate being responsible for diseases (Madsen et al., 2000;Martins et al., 2002).Nothing is known about trichodinid species from pond-reared fishes in Brazil.In this study, Trichodina magna Van As and Bassson, 1989, found on the skin and gills of tilapia, Oreochromis niloticus Linnaeus, 1758 collected in three regions in the State of Santa Catarina, Brazil, is described.

Material and Methods
Specimens of O. niloticus were collected in farms situated in the municipalities of Blumenau (26° 55' 10'' S and 49° 03' 58'' W) (n = 48), Joinville (26° 18' 16'' S and 48° 50' 44'' W) (n = 63), and Ituporanga (27° 24' 52'' S and 49° 36' 09'' W) (n = 35), Santa Catarina, Brazil, from October 2004 through June 2005.Wet smears of skin and gills were prepared in the field and examined under microscope.When parasites were present the smears were air dried and impregnated with Klein's dry silver method for observation of the adhesive disc as suggested by Lom (1958).Other smears were stained with Giemsa's solution to reveal the nuclear apparatus.The span of the denticle was measured from the tip of blade to the tip of ray as described by Arthur and Lom (1984a).The body diameter is the dimension of the adhesive disc plus the border membrane, and the diameter of the striated membrane is the distance from the outer border of the adhesive disc to the denticulate ring.Wet mounts from the specimens preserved in 5% formalin solution were studied for the observation of adoral ciliature.All measurements are in micrometers and follow the recommendations of Lom (1958) and Van As and Basson (1989).Arithmetic means ± standard deviation is followed, in parentheses, by the minimum and maximum values and number of specimens or structures measured.t-test was applied to compare the measurements (from the averages) of these specimens with the original description.

Results
From a total of 146 examined fish, 36 were parasitized on the skin, 14 in the gills and 33 on the skin and gills.The parasite was characterized as a large trichodinid with disc-shaped body; convex adoral surface with ciliature of about 370° ± 6.7 (360-384) measured in 17 specimens; central contractile vacuole; aboral side with slightly concave adhesive disc provided by 26.0 ± 1.2 (23-29, 55) denticles and central area of the adhesive disc provided with dark granules.The denticles are inserted into one another characterized by blade slightly falcate with a smooth anterior margin; central part very long and sharppointed in Giemsa-stained specimens, but slightly robust in silver-impregnated specimens reaching y + 1 axis; ray long and slender anteriorly directed but do not pass y + 1 axis, slightly curved tapering gradually along its length provided by a relatively long apophysis (Figure 1).
The apophysis morphology of the prominent ray of the denticle had a similar structure, although Van As and Basson did not give its measurements.The micronucleus was not detected corroborating the findings of Van As and Basson (1989).Another point that must be considered is that, in silver-impregnated specimens, the length of the apophysis of the ray may vary or may not even be detectable.Based on this information, commented by Vans As and Basson (1989), the apophysis measurements in Giemsa-stained specimens were performed in this study.The unique most distinguishable difference was the fact that the ray of denticle is anteriorly directed, extending over the y + 1 axis in the specimens of Van As and Basson (1989) (Figure 2) while in the present description the ray is situated between the y and y + 1 axes.In spite of the difference in position of the ray in relation to the axes and the lack of significant difference in morphology these specimens must be considered members of T. magna.This study shows the variability that can be seen in the different populations of trichodinid species, corroborating the observations of Van As and Basson (1989).Figuras -BJB oman), tamanho 8. s com 0.5 de Stroke.tes a "Dados gráficos" com 0.6 de Stroke.ver rosa do ventos na imagem original, substituir pela padrão da paleta symbol.e barras com 10% de preto quando houver texto e 50% quando não.ou figura devem estar todos em Inglês.estar dentro de caixas de texto com 2 mm de distância nas extremidades.u gráfico deve estar em "Sentence case".deverá ter 1 ponto de Stroke.sentam figuras ex: , devem estar no canto superior direito com 2 mm de midades da figura.and Basson (1989)

Figure 1 .
Figure 1.Photomicrographs of Trichodina magna from Oreochromis niloticus cultured in the State of Santa Catarina.Stained by Giemsa (a-b) and silver impregnated specimens (c-d).

Figure 2 .
Figure 2. Diagrammatic representation of the denticles of the present description a) and b) Trichodina magna Van Asand Basson (1989)