Hoplias malabaricus (Bloch, 1794)

Blanco, Daniel Rodrigues, Lui, Roberto Laridondo, Bertollo, Luiz Antonio Carlos, Margarido, Vladimir Pavan & Filho, Orlando Moreira, 2010, Karyotypic diversity between allopatric populations of the group Hoplias malabaricus (Characiformes: Erythrinidae): evolutionary and biogeographic considerations, Neotropical Ichthyology 8 (2), pp. 361-368 : 362-364

Hoplias malabaricus from the São Francisco River basin

The specimens from this population had 2n = 42 chromosomes (22 m + 20 sm) and Fundamental Number ( FN) = 84 in both males and females, with no chromosome heteromorphism related to sex. C-banding revealed pericentromeric bands in the majority of chromosomes; some chromosomes also exhibited terminal and interstitial bands. Submetacentric pair 17 clearly stood out, with a large band in the terminal region of the long arm, which were co-localized with the Ag-NORs ( Fig. 1a, b, c ). Fluorescent in situ hybridization ( FISH) with the 5S rDNA probe revealed two chromosome pairs with interstitial sites: one small metacentric pair (n 10) with sites in the long arm and one large submetacentric pair (n 13) with sites in the short arm near the centromere ( Fig. 2a ). 18S rDNA sites were found in four chromosome pairs: two metacentric pairs (n 6 and 9) with sites located in the terminal region of both chromosome arms and two submetacentric pairs (n 16 and 17) with sites in the long arms in the region near the centromere and the terminal region, respectively ( Fig. 2b ). FISH with the 5 S Hind III satellite DNA probe identified nine chromosome pairs with sites in the centromeric region: three metacentric pairs (n 1, 5 and 6) and six submetacentric pairs (n 12, 13, 14, 18, 19 and 21) ( Fig. 2c ) .

Hoplias malabaricus from the Araguaia River basin

The specimens collected in São Miguel do Araguaia had 2n = 42 chromosomes (18 m + 24 sm) and FN = 84 in both males and females, with no chromosome heteromorphism related to sex. Heterochromatin was found distributed in the pericentromeric and terminal region in several chromosomes of the complement. Submetacentric pair 10 clearly stood out, with a large band in the pericentromeric region; pairs 14 and 20 had conspicuous bands in the terminal region of the long arm, which were co-localized with the Ag-NORs ( Fig. 1d, e, f ). FISH with the 5S rDNA probe revealed only one small metacentric pair (n 8) labeled in the interstitial region of the long arms ( Fig. 2d ). 18S rDNA sites were labeled in three pairs of submetacentric chromosomes: one large pair (n 10) in the region near the centromere and two smaller pairs (n 14 and 20) in the terminal region of the long arms. Moreover, only one of the homologues of pair 10 had an extra site, which was in the terminal region of the long arm ( Fig. 2e ). FISH with the 5 S Hind III satellite DNA probe identified eight chromosome pairs with sites in the centromeric region: two metacentric pairs (n 1 and 5) and six submetacentic pairs (n 10, 11, 12, 15, 16 and 21) ( Fig. 2f ) .

Hoplias malabaricus from the basin of the Xingu River

The specimens collected from the tributaries of the Sete de Setembro River had 2n = 42 chromosomes (20 m + 22 sm) and FN = 84 for both males and females, with no heteromorphic sex chromosome system. C-banding revealed pericentromeric bands in nearly all the chromosomes as well as small terminal bands on some pairs. Silver nitrate staining revealed three chromosome pairs (n 4, 9 and 15) withAg-NORs ( Fig. 1g, h, i ). FISH with the 5S rDNA probe revealed only one metacentric pair (n 8) labeled in the interstitial region of the long arms ( Fig. 2g ). 18S rDNA sites were labeled in the terminal region of the long arms in three pairs of chromosomes: two metacentric pairs (n 4 and 9) and one submetacentric pair (n 15) ( Fig. 2h ). FISH with the 5 S Hind III satellite DNA probe identified 10 chromosome pairs with sites in the centromeric region: four metacentric pairs (n 1, 5, 7 and 10) and six submetacentric pairs (n 11, 12, 13, 16, 17 and 19) ( Fig. 2i ) .

Figures

Fig. 1. Hoplias malabaricus karyotypes (karyomorph A) with conventional Giemsa staining (a, d, g) and C-banding (b, e, h) of the populations from the basins of the São Francisco (a, b), Araguaia (d, e) and Xingu (g, h) Rivers. Boxes display chromosomes with Ag-NORs in the populations from the São Francisco (c), Araguaia (f) and Xingu (i) Rivers. Scale bar = 5μm.

Fig. 2. Hoplias malabaricus karyotypes (karyomorph A) with fluorescent in situ hybridization (FISH) using 5S rDNA (a, d, g), 18S rDNA (b, e, h) and 5SHindIII satellite DNA (c, f, i) probes in the populations from the basins of the São Francisco (a, b, c), Araguaia (d, e, f) and Xingu (g, h, i) Rivers. Scale bar = 5μm.