Chromosomal variability in the wild ornamental species of Symphysodon (Perciformes: Cichlidae) from Amazon

Débora R Mesquita,Eliana Feldberg,Jorge I R Porto

doi:10.1590/s1679-62252008000200005

Débora R Mesquita, Eliana Feldberg + Show 1 more

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https://doi.org/10.1590/s1679-62252008000200005

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Abstract

Cytogenetic studies were conducted on three discus species which inhabit the Amazon in Brazil: Symphysodon haraldi from Manacapuru, S. aequifasciatus from Tefé and S. discus from Barcelos. All individuals showed 2n=60 chromosomes, most of them biarmed. No sexual chromosomal heteromorphism was verified. However, different karyotypic formulae, owing to the presence of subtelocentric chromosomes, were verified for S. aequifasciatus and S. discus. One of the karyotypic formulae from S. aequifasciatus (cytotype 2) differs from the others, due to one of the homologues in the first chromosome pair being significantly larger than the other. A large variability was observed toward the nucleolar organizer regions (NOR) of S. haraldi and S. aequifasciatus. Although the number of silver-stained blocks varied from 2 to 5, confirming different NOR patterns, at least seven homologue pairs were involved with NORs. In S. discus only two marks were observed, however two chromosome pairs were involved, characterizing a multiple NOR system for the three species. The heterochromatic blocks were mainly located in the pericentromeric region of all chromosomes but, in some of them, they are also located in the proximal regions, both in the short and long arms. Moreover, in the cytotype 2 from S. aequifasciatus, an interstitial heterochromatic block was observed on the long arm of the largest homologue of the first pair. A direct comparison of karyotypes from more related genera (Heros, Uaru, Mesonauta and Pterophyllum), makes it clear that a succession of chromosomal rearrangements, mainly pericentric inversions, translocations and fissions/fusions occurred resulting in the present diploid number and intraspecific karyological variability found in Symphysodon.

Highlights

In Brazil, the Amazon basin is responsible for more than 90% of all ornamental fish exported to North American, European and Asian markets and the revenues generated by this trade is valued at approximately 3 million US$ annually (Chao, 2001)
Ready et al refer to the Blue and Brown discus as S. aequifasciatus, while Bleher et al recognize them as S. haraldi
Discus specimens were collected from natural habitat in the Amazon Basin and were identified according to diagnostic keys provided by Ready et al (2006), Bleher (2006) and Bleher et al (2007), and we opted to follow Bleher’s taxonomy, i.e., S. aequifasciatus (Green discus), S. haraldi (Brown/Blue discus) and S. discus (Heckel discus)

Summary

Introduction

In Brazil, the Amazon basin is responsible for more than 90% of all ornamental fish exported to North American, European and Asian markets and the revenues generated by this trade is valued at approximately 3 million US$ annually (Chao, 2001). The discus fish is characterized by a colourful and compressed disk-shaped body that captures the attention of aquarium hobbyists worldwide, making it one of the most demanded Amazonian fish in the ornamental fish trade (Goldstein, 1973; Silva & Kotlar, 1980; Axelrod, 1995). Symphysodon currently includes three species: S. discus Heckel, 1840 (Heckel Discus), S. aequifasciatus Pellegrin, 1904 (Blue or Brown Discus) and S. tarzoo Lyons, 1959 (Green Discus) (Ready et al, 2006) or S. discus, S. haraldi Schultz, 1960 and S. aequifasciatus (Bleher, 2006; Bleher et al, 2007). Ready et al refer to the Blue and Brown discus as S. aequifasciatus, while Bleher et al recognize them as S. haraldi

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