C 1997 The Japan Mendel Society Cytologia 62: 171-176, 1997

Karyotypes of Five Tetragonopterinae Species (Pisces, ) from Argentina

A. J. Alberdi and A. S. Fenocchio Departamentode Genetica, Facultad de CienciasExactas, Quimicas y Naturales, UniversidadNacional de Misiones,Felix de Azara 1552,3300 Posadas, Misiones, Argentina AcceptedMarch 5, 1997

The Characidae family is one of the most specious within the Order and includes with different morphological and ethological patterns and food-habits (Britski et al. 1986). The subfamily Tetragonopterinae comprises many forms of small fishes commonly called "mojarras", which are usually breed as ornamental fishes. It is believed that this subfamily represent an artificial group because of the morphological diversity of its species and also of the very different karyotypic situations detected (Portela et al. 1988). Cytogenetic studies made in the Tetragonopterinae have shown a wide range of 2n values from 2n = 36 (Astyanax schubarti: Morelli et al. 1983) to 2n = 52 (Tetragonopterus chalceus, Piabina argentea, Bryconamericus stramineus: Portela et al. 1988). This variability is related to a large diversity of karyotypic formulae, place and size of nucleolus organizer regions (NORs), and also to the location and amount of constitutive heterochromatin (Morelli et al. 1983, Portela et al. 1988, Moreira Filho and Bertollo 1991). However, the fishes of this group share the presence of a larger 1st chromosome pair. This fact is an important cytotaxonomic character observed for the first time by Scheel (1972) and widespread in the Characidae (Morelli et al. 1983). In the present study, five species of the Tetragonopterinae from Argentina were cytogen- etically analyzed.

Materials and methods Karyotypic studies were performed on five species belonging to the Tetragonopterinae (Pisces, Characidae) collected in Parana, river (Posadas, Misiones, Argentina) and Aguapey river (Corrientes, Argentina). Astyanax schubarti (1 female from Parana river), A. bimacul- atus (25 males, 10 females and 4 undeterminated sex from Parana,-Aguapey rivers), Gymnoco- rhimbus ternetzi (1 male, 2 females and 1 undeterminated sex from Parana river), Moenkhausia sanctaefilomenae (1 male and 1 female from Aguapey river) and Tetragonopterus argenteus (1 female and 4 undeterminated sex from Parana river). Mitotic preparations were obtained from the kidney tissue by direct methods (Bertollo et al. 1978, Foresti et al. 1993) and short term culture (Fenocchio et al. 1991). Each of C and NOR-banding was carried out by the methods described by Summer (1972) and Howell and Black (1980), respectively. Chromosome morphology was determined on the basis of arm ratios as proposed by Levan et al. (1964): metacentrics (M), submetacentrics (SM), sub- telocentrics (ST) and acrocentrics (A).

Results The studied species showed the following chromosome numbers: 2n = 36 (Astyanax

Corresponding author: A. S. Fenocchio, e-mail: alberto@misiones. org. ar@genetica. unam. edu. ar 172 A. J. Alberdi and A. S. Fenocchio Cytologia 62

Table 1 . Number of analyzed cells and modal diploid number of each species

Table 2 . Karyotypes of the five Tetragonopterinae species

schubarti), 2n = 50 (Astyanax bimaculatus, Gymnocorhimbus ternetzi and Moenkhausia sanctae- filomenae) and 2n = 52 (Tetragonopterus argenteus) (Table 1). It was observed in all species that the 1st pair of M, is the largest chromosome of the karyotype. The size ratio between this first pair and the second one on the karyotype is smaller in T. argenteus than in the other species (Fig. 1). The two populations of A. bimaculatus showed a similar karyotype, with 10 M, 18 SM, 12 ST and 10 A chromosomes (Fig. 1a). C-banding was generally of poor quality. Pale stained regions were observed at centromeric and telomeric regions of several chromosome pairs, and more stained regions in short arms on a ST pair. The NORs were detected in telomeric regions and marks 1 to 6 chromosomes, preferently of ST-A. A dark block was found in the first pair of ST. A ST chromosome with a NOR in the telomeric region on both chromosome arms was also observed (Fig. 2c). A. schubarti shows 14 M, 14 SM, 6 ST and 2 A. These elements are bigger than those observed in other species of Astyanax (Fig. lb). Only one pair of NORs were detected, the marks are located at telomeric regions of a small A chromosome (Fig. 2e, f) . G. ternetzi had a karyotype composed of 14 M, 12 SM, 6 ST and 18 A (Fig. 1d). NORs were observed in the short arm of only one ST pair (Fig. 2d). M. sanctaefilomenae presents 48 M-SM and 2 ST-A (Fig. lc). In one specimen it was detected the presence of 1, 2 or even 3 supernumerary microchromosomes. T. argenteus showed 2n = 52 with 16 M-SM, 2 ST and 34 A (Fig. 1e). The C-banding has showed two patterns as an individual polymorphism. In one case it was observed large blocks that include the short arms of a pair of ST. In the other case this pattern was also observed but accompained by centromeric bands in A, and telomeric bands in short arm of ST (Fig. 2a) . The NORs were placed on the short arm of one pair of ST chromosomes (similar observations were performed by Portela et al. 1988 in T. chalceus) (Fig. 2b). In no species were observed chromosome differences between males and females. 1997 Karyotypes of Five Tetragonopterinae Species 173

a

b

C

d

e

Fig. 1. Karyotypes (Giemsa staining). a: Astyanax bimaculatus (Aguapey river) (2n=50), b: A. schubarti (2n=36), c: Moenkhausia sanctaefilomenae (2n=50), d: Gymnocorhimbus ternetzi (2 n=50) and e: Tetragonopterus argenteus (2n=52). 174 A. J. Alberdi and A. S. Fenocchio Cytologia 62

a b

c d

e f

Fig. 2. Tetragonopterus argenteus. a: C-banding, b: NOR banding, c: Astyanax bimaculatus (Aguapey river) and d: Gymnocorhimbus ternetzi (NOR banding), e and f: Astyanax schubarti (sequential staining e: Giemsa, f: NOR banding). The arrows indicate NOR chromosomes.

Discussion

This study reports new karyotypic data about a very specious group and represents the first cytogenetic approach to tetragonopterins from Argentina. The present study supports previous observations about Astyanax, describing and evidenc- ing differences between A. bimaculatus and A. schubarti in the diploid number , NOR patterns, and in the size of chromosomes. In A. bimaculatus from two different basins was not observed 1997 Karyotypes of Five Tetragonopterinae Species 175 cytogenetical differences. A. schubarti are characterized by similar karyotypic formulae to those described by Morelli et al. (1983). M sanctaefilomenae shows a similar karyotype (2n= 50) to that studied previously by Foresti et al. (1989). G. ternetzi, presents 2n = 50 with high number of A chromosomes and only one NOR pair (Scheel 1972, Krishnaja and Rege 1980). In these four species the 1st pair is very larger than the rest of chromosomes, as have been reported by Scheel (1972) for the Characidae family. The karyotype and NOR pattern of Tetragonopterus argenteus seems to be very similar to that of T. chalceus analyzed by Portela et al. (1988). This shows unexpressive size differences between the 1st chromosome pair and the rest of karyotype, indicating the probable loss of chromatin during evolution. The NORs are also C-positive as in the other - gonopterinae species (Moyses and Almeida Toledo 1995).

Summary Karyotypic studies on five species (Characidae, Tetragonopterinae) from Argentina were carried out. Mitotic preparations from the kidney tissues were made by direct and short term culture methods. C-banding and silver staining was performed by conventional techniques. Astyanax bimaculatus, Gymnocorhimbus ternetzi and Moenkhausia sanctaefilomenae showed 2n = 50 chromosomes, with different karyotypic formulaes. Tetragonopterus argenteus showed 52 chromosomes and Astyanax schubarti 2n = 36 chromosomes. One pair of NORs was detected in most of species except in A. bimaculatus which showed numerical variation (1-6 carrier chromosomes) and size heteromorphism. The present paper reports the first cytogenetic study on the Tetragonopterinae from Argentina.

Key words : Cytogenetics, Fishes, Characiformes, Characidae, Tetragonopterinae, Neotropi- cal region.

Acknowledgements We are grateful to Lics. Pastori, Lopez, Sanchez and Roncati for their valuable help and to MSc G.M. Duarte for help in the final correction of manuscript.

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