First Record of Trichodina compacta Van As and Basson, 1989 (Protozoa: Ciliophora) from Cultured Nile Tilapia in theState of Santa Catarina, Brazil

MATERIALS AND METHODS

The fish utilized in this experiment were collected in farms situated in the cities of Blumenau (26°55’10’’S, 49°03’58’’W) (n = 48), Joinville (26°18’16’’S, 48°50’44’’W) (n = 63) and Ituporanga (27°24’52’’S, 49°36’09’’W) (n = 35), Santa Catarina, Brazil for a period of October 2004 to June 2005. Wet smears of the 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 impregnation method for adhesive disc observation as suggested by Lom (1958). Other smears were stained with Giemsa’s solution to reveal the nuclear apparatus. The span of denticle is measured from the tip of blade to the tip of ray (Arthur and Lom, 1984b). The body diameter is the dimension of adhesive disc plus border membrane and the striated membrane is the distance from the outer border of the adhesive disc to 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 followed the recommendations of Lom (1958), Van As and Basson (1989). Arithmetic means±standard deviation followed by minimum and maximum values and the number of specimens and structures measured are in parentheses. To compare the measurements of our material with those until then described the t-test was applied.

RESULTS

Trichodina compacta Van As and Basson, 1989
Synonyms: Trichodina truncata Ghiraldelli, 2005
Host: Oreochromis niloticus Linnaeus, 1758
New localities: Cities of Blumenau, Joinville and Ituporanga, SC, Brazil

From a total of 146 examined fish, 36 were parasitized by trichodinids on the skin, 14 in the gills and 33 on the skin and gills. Characterized as a small trichodinid with disc-shaped body 50.8±8.0 (31-71, 54) in diameter; convex adoral surface with ciliature of about 373°±6.4 (370-384) measured in 10 fresh-mounted specimens; contractile vacuole central. Its body is surrounded by thin border membrane 5.6±2.2 (2-8, 34) wide; width of striated membrane 6.8±1.9 (2-14, 43). Aboral side with adhesive disc concave 32.8±4.7 (19-40, 54) in diameter. Central area of the adhesive disc well defined and clear, delimited by a central circle 8.5±1.1 (6-10, 23) in diameter containing darker spots, in which the edges of rays of denticles are frequently supported. Denticulate ring diameter 21.9±3.1 (16-32, 51) provided by 17±0.9 (15-19, 54) denticles (Fig. 1).

The denticles are characterized by blade truncate not completely filling the sector between y and y+1 axes, with an apophysis in the anterior margin. Central part long and sharp-pointed in Giemsa-stained specimens, but shorter, robust and tip bluntly in silver-impregnated specimens not passing the half way between y and y+1 axes (Fig. 2).

Fig. 1:	Diagrammatic representation of the denticles of Trichodina compacta from Oreochromis niloticus cultured in the State of Santa Catarina, Brazil (a), Israel (b) and South Africa (c) redrawn from Van As and Basson (1989)

Fig. 2:	Photomicrographs of Trichodina compacta Van As and Basson, 1989 from Oreochromis niloticus cultured in the State of Santa Catarina. Silver impregnated (A) and stained by Giemsa (B) specimens. Scale-bars = 20 μm

The connection of the central part of denticle is little distinguishable from blade or ray. Ray short and stout anteriorly directed but do not pass y+1 axes, slightly curved, point of ray rounded. The anterior apophysis of the prominent ray was clearly visible only in Giemsa stained specimens while apophysis of blade is easily visible in silver-impregnated ones. Radial pins per denticle 7.0±0.7 (6-8, 42); length of denticles 9.8±2.5 (6-19, 67), length of blade 3.5±1.2 (1-6, 67), width of central part 1.9±0.9 (1-3, 67), length of ray 5.9±0.9 (3-7, 67), length of ray apophysis 0.9±0.3 (0.6-1.3, 12); denticle span 13.7±2.5 (9-19, 67). Macronucleus horseshoe-shaped 30.0±2.9 (25-38, 21) in diameter, 7.0±1.1 (6-9, 21) thickness, length between the terminations of macronucleus 10.7±2.4 (7-16, 21). Micronucleus not detected. The specimens are in the collection of author.

DISCUSSION

This research studied again Trichodina truncata Ghiraldelli, 2005 especially on its denticle morphology and position in relation to y and y+1 axes. The original description showed the following characteristics in comparison to other species. The material collected at three different localities in the State of Santa Catarina was similar to T. nigra luciopercae Lom, 1970; to T. heterodentata; to T. compacta and to T. acuta Lom, 1961 (Duncan, 1977; Imai et al., 1991) in its diameter of body and denticulate ring. From T. nigra luciopercae, T. heterodentata and T. acuta our specimens showed smaller number of denticles. From T. canton differs in having shorter adhesive disc diameter, denticulate ring, denticle dimensions, low number of denticles and by absence of central circle. The number of denticles is an important differential diagnosis and was similar to T. microspina Van As and Basson, 1992; T. kalimbeza and T. minuta, but did differ in the morphology of denticles and other measurements. According to Van As and Basson (1989) the number of denticles may present a slight variation between the species and is also related to the evolution of the parasites in its life cycle. During the binary fission trichodinids show reduced to half the number of denticles, but present the formation of peripheral new denticulate ring. This fact was not observed in our material concluding that the specimens were in its advanced stage of development. Present material showed the largest measurements and different morphology of denticle when compared to T. giurusi Mitra and Haldar, 2005 and T. molae Mitra and Haldar, 2005 from freshwater Indian fishes. In spite of the similar measurements of the body, denticulate ring and ray of T. notopteridae Mitra and Haldar, 2004 the present description showed different number of denticles and blade morphology, as well as the fish host and locality.

There was a very similar measurements of the denticles blade length when compared to T. jadranica Haider, 1964 (Arthur and Lom, 1984a), T. microspina, T. minuta and T. compacta; and in denticle length compared to T. domerguei (Lom, 1960). Apophysis in the anterior margin near base of blade was also observed in T. heterodentata, T. acuta and T. compacta. The most similar specimen was T. compacta originally described by Vans As and Basson (1989) in Oreochromis andersoni, O. mossambicus, Tilapia rendalli rendalli, T. rendalli swerstrae, T. sparrmanii in South Africa; O. aureus and the hybrid O. aureus x O. niloticus in Israel. Present material showed similar dimensions of body diameter, border membrane width, denticulate ring diameter and blade length (Table 1). On the other hand, it differs from T. compacta in having smaller adhesive disc diameter; smaller number of denticles and pins per denticle, but larger denticle length and ray. Important characteristic was the fact that the central circle into denticulate ring was smaller than in T. compacta.

Table 1:	Comparative measurements of Trichodina compacta from Santa Catarina, Brazil and the descriptions of Van As and Basson (1989) from South Africa (a) and Israel (b)
LTDistance between terminations of macronucleus. Different letters indicate significant difference between the specimens Values in parenthesis shows variation amplitude

Present specimens showed blade truncate not completely filling the sector between y and y+1 while T. compacta from Israel the blade is broad filling that sector and in specimens from South Africa the blade passes the y+1 axis (Fig. 1). The central part of denticle in T. compacta described by Van As and Basson (1989) is slightly sharp pointed while our material is robust. In the original description of T. compacta the posterior tip of central part extends to halfway to y-1 axis such as in the present specimens. In spite of the shortest denticulate ring, adhesive disc, slightly lower number of denticles, largest measurements of denticle length and ray and a very similar denticle shape (Fig. 1) when compared to the original description of T. compacta, we suggest that the present material it does not a new species. The considerable variation within the population of trichodinids on cultured tilapia was discussed by Van As and Basson (1989) and can be well adapted to the present description.

Although the number of denticles was different the specimens belongs to another population of T. compacta in Brazil based on its denticle morphology. This study re-evaluate previously described T. truncata by Ghiraldelli (2005) in tilapia based on denticle morphology and its position in relation to y and y+1 axes. Trichodina truncata fall within the characteristics of T. compacta, being a new record in the Brazilian cultured tilapia. The authors emphasize the importance of the Brazilian trichodinid identification as being an opportunistic and sometimes pathogenic parasite. In spite of a great number of trichodinid species over the World this work present significant contribution to the knowledge of the Brazilian trichodinid species.

ACKNOWLEDGMENTS

To CAPES and CNPq for granting a Master Science and Research scholarship, respectively to the first, second and third authors. To Roberto Hoppe (Fundação 25 de Julho), Sérgio Tamassia (Epagri), Pesque-pague Erimar, Pesque-pague Fernandão, Pesque-pague Divisa, Nilotica Aquacultura, Amilton Luiz, Aurima Knaul, Jair Curti Vegge, João Carlos Desordi, Valério Burini for fish donation. To Gastão Reis and Heloisa Laterça for correction of the manuscript translation.