Paratrichodina africana ( Ciliophora : Trichodinidae ) of wild and cultured Nile tilapia in the Northern Brazil Paratrichodina africana ( Ciliophora : Trichodinidae ) de tilápia do Nilo selvagem e cultivada no Norte do Brasil

The present work morphologically characterizes Paratrichodina africana from the gills of wild and farmed Nile tilapia from Northern Brazil (eastern Amazonia). Ninety fish were captured for parasitological analysis in Macapá, State of Amapá, from a wetland area bathed by the Amazon River commonly called ‘Ressaca do Zerão’ (n = 52), as well as from a local fish farm (n = 38). Wet smears of the skin and gills of the captured fish were air dried at room temperature and impregnated with silver nitrate by Klein’s method for posterior examination of the adhesive disc structures. Total prevalence of parasitism was 16.6% (23% in fish from wetland and 7.8% in farmed fish). Characterized as a small-sized trichodinid, it presented the following measures: 33.2 ± 4.7 μm body diameter, 17.5 ± 2.1 μm adhesive disc, 10.0 ± 0.9 μm denticulate ring, and 22.6 ± 2.0 denticles. Paratrichodina africana reported in this study strongly resembles those described for other localities, but it differs by presenting greater body length. This is the fourth report of P. africana parasitizing a host fish.


Introduction
Trichodinid ciliates are one of the most common fish ectoparasites in the aquatic environment (BASSON; VAN AS, 2006).Besides, this ciliated protozoan is able to cause considerable damage to farmed tilapia Oreochromis niloticus Linnaeus, 1758 in Brazil (GHIRALDELLI et al., 2006a), especially under inadequate handling conditions (MADSEN et al., 2000;MORAES;MARTINS, 2004).Braccini et al. (2008) observed the presence of trichodinids in tilapia kept in cages in the Corvo and Guairacá Rivers, Paraná state, and suggested that the amount of parasites is directly related to environmental quality.Evans et al. (2007) infected two groups of channel catfish (Ictalurus punctatus) fingerlings, parasitized and non-parasitized by Trichodina sp., with Streptococcus iniae and Streptococcus agalactiae.The mortality rate was significantly higher in fish that were coinfected.In addition, the studies by Martins et al. (2011) demonstrated reduction in vaccine performance in tilapia parasitized by Trichodina.
This study morphologically characterizes Paratrichodina africana Kazubski & El-Tantawy, 1986 from wild and farmed Nile tilapia in eastern Amazonia.Prevalence and a list of comparative measures are also provided.

Materials and Methods
Ninety specimens of non sex-reversed Nile tilapia O. niloticus of 8.6-29.0cm total length (17.8 ± 5.4) and 12.0-396.0g (126.7 ± 92.2) were collected in Macapá, State of Amapá between December 2009 and November 2010 from two distinct areas: a wetland area bathed by the Amazon River commonly called 'Ressaca do Zerão' (00° 00' 09.8" N and 051° 05' 25.2" W) (n = 52) and a local fish farm (00° 02 ' 31.4" S and 051° 07' 34.4" W) (n = 38).The fish were transferred alive to the Laboratory of Aquaculture and Fisheries at 'Embrapa Amapá' for parasite examination Wet smears of the skin and gills of the captured fish were air dried at room temperature and impregnated with silver nitrate by Klein's method for posterior examination of the adhesive disc structures and denticles under optical microscopy, as suggested by Lom (1958).All measures (in micrometers) were taken in camera lucida.The span of the denticle was measured from the tip of the blade to the tip of the ray, as described by Arthur and Lom (1984).Arithmetic means ± standard deviation is followed, in parentheses, by the minimum and maximum values, and the number of structures measured.Denticles description follows the recommendations by Van As and Basson (1989).Specimens were deposited in the National Institute of Amazonian Research (INPA), Manaus, AM, Brazil.

Results
Description based on 40 specimens: characterized as a small sized trichodinid (Table 1, Figure 1a).Adoral ciliary spiral 260°.Shape of blade resembles an equilateral triangle with vertex angle directed towards to the adhesive disc center.Distal surface of blade rounded.Tangent point situated just below distal point of distal surface.Anterior surface usually with rounded tips without touching y-axes (Figure 2).Posterior surface of blade deeply curved.Blade connection thin and long.Distinct central part, with a spine-like processus in its tip, which extends halfway towards y-1 axis (Figure 2).Ray slightly shorter than blade, straight, narrow, finger-shaped and distinctly concave at base of posterior surface.Ray apophysis absent.Wide border membrane surrounding the adhesive disc, measuring about 2.24 µm in width.Horse-shoe shaped macronucleus 17.0 µm in diameter and 2.6 µm in width (Figure 1b).Micronucleus not viewed.

Remarks
Paratrichodina africana was first described in Nile tilapia by Kazubski and El-Tantawy (1986).The authors allocated the species to the genus Paratrichodina due to the presence of two important features: the straight blade, in line with the radius of the adhesive disc and the absence of incision at the base of the blade, where the central part of the neighbouring denticle could enter.Later, the species was reported in Oreochromis mossambicus in West Bengal, India by Mitra and Bandyopadhyay (2006) and in O. niloticus in Northern Brazil by Pantoja et al. (2012).
Paratrichodina Lom, 1963 comprises approximately 14 species, all characterized by small body dimensions and occurrence in the gills of the host (except for Paratrichodina phoxini, P. alburni, and P. degiustii -all endoparasites of the urinary tract).Paratrichodina incisa, the genus type, shows great similarity with P. africana in respect to some morphological features (Table 2).However, it differs from the latter by presenting a smaller and less rounded spine-like processus continuous with the central part.In addition, the distal surface of the blade of P. incisa is clearly straight, whereas it tends to be rounded in P. africana.Paratrichodina lizae also  presents biometrical data similar to the present species (Table 2).However, as reported by Mitra and Bandyopadhyay (2006), the species contains one to eight non-impregnable round particles in the central part of the adhesive disc, which are absolutely absent in P. africana.Lom (1963) reported "If there is an anterior projection near the base of the blade, it does not communicate with a notch in the blade of the preceding denticle".Later, Gaze and Wootten (1999) illustrated the distinct interlocking mechanism of the denticles of P. incisa and better elucidated the positioning of the anterior projection, describing it as a well-defined structure continuous with the central part.
Gaze and Wootten (1999) suggested the absence of ray apophysis in P. incisa as an additional discriminating feature of the genus.Our observations support this idea since it was also not recorded in the specimens of P. africana herein observed.
Paratrichodina africana reported in this study fall within the ranges for P. africana presented in the original description by Kazubski and El-Tantawy (1986) with respect to measures of body diameter, number of denticles, denticulate ring, size of adoral spiral, and wide border membrane.The subsequent report provided by Mitra and Bandyopadhyay (2006) also presents similar measures of the denticulate ring, number of denticles, pins per denticle, and some dimensions of denticle components, but it differs in body diameter (Table 1).Additionally, all other Paratrichodina species biometrically differed from the present studied specimens, as presented in Table 2.

Conclusion
This is the fourth register of P. africana parasitizing a fish host and the first report of the genus in eastern Amazonia.By the fact that tilapia is one of the most popular and cultured freshwater fish, fish farmers must be careful with the water quality and feeding rate in ponds and especially in cages when the fish stocking density are higher than normal predisposing the fish for parasitism.

Figure 2 .
Figure 2. Diagrammatic representation of the denticles of Paratrichodina africana from Oreochromis niloticus in the State of Amapá, North of Brazil.

africana Present study Paratrichodina africana Kazubski and El-Tantawy, 1986 Paratrichodina africana Kazubski and El-Tantawy, 1986 in Mitra and Bandyopadhyay, 2006
The averages ± standard deviation are followed by minimum and maximum values and the number of structures or specimens measured in parenthesis.D Diameter, L Length, W Width.