Corresponding author: Ana Claudia Swarça ( firstname.lastname@example.org )
Academic editor: Ekaterina Gornung
© 2017 Ana Claudia Swarça, Ana Lucia Dias, Alberto Sergio Fenocchio.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Swarça AC, Dias AL, Fenocchio AS (2017) Cytogenetic studies in the redtail catfish, Phractocephalus hemioliopterus (Bloch & Schneider, 1801) (Siluriformes, Pimelodidae) a giant fish from Amazon basin. Comparative Cytogenetics 11(1): 119-128. https://doi.org/10.3897/CompCytogen.v11i1.11152
The objective of this study was to cytogenetically analyze Phractocephalus hemioliopterus comparing the findings with other data to infer relationships among Pimelodidae species. The results revealed a diploid number of 2n = 56 and the karyotype composed of 16 metacentric, 20 submetacentric, 6 subtelocentric and 14 acrocentric chromosomes (FN = 98). The Ag-NORs, 18S rDNA and CMA3 signals were coincident in location occupying the short arm of an acrocentric chromosome pair (23th), in a secondary constriction. The 5S rDNA genes were localized near the centromere on the short arms of one submetacentric chromosome pair. C-bands were localized predominantly in the terminal regions of chromosomes, including the AgNORs and a small metacentric pair with a conspicuous positive band on interstitial region. This chromosome pair could be considered a species-specific cytogenetic marker.
Neotropical fish, Parrot catfish, karyotype, Ag-NORs, 18S rDNA, CMA3, C-banding
The genus Phractocephalus Agassiz, 1829 belongs to Pimelodidae family and contains three species, one extant, Phractocephalus hemioliopterus (Bloch & Schneider, 1801) and two extinct species recently described, P. nassi (Lundberg and Aguilera, 2003) and P. acreornatus (
The large catfish, P. hemioliopterus, has a wide distribution in the lowland, meandering rivers and lagoons of the Orinoco, Amazon and Essequibo (
From a systematic point of view, Pimelodidae remains as a controversial group, possessing some internal inconsistencies, represented by the “Pimelodus group”, “Calophysus group” and a basal branch including three genera Phractocephalus, Leiarius Bleeker, 1862 and Perrunichthys Schultz, 1944 (
Available cytogenetic data partially support this hypothesis because several chromosomal studies on Pimelodidae have revealed that the species of this family have a predominant diploid number of 56 (Table
Cytogenetic data on the family Pimelodidae. 2n = diploid number. Only published data were used.
|Bergiaria Eigenmann & Norris, 1901||56||
|Iheringichthys Eigenmann & Norris, 1900||56||
|Parapimelodus La Monte, 1933||56||
|Pimelodus Lacepède, 1803||Predominant 56||
|Calophysus Müller & Troschel, 1843||50||
|Pinirampus Bleeker 1858||50||
|Luciopimelodus Eigenmann & Eigenmann, 1888||50||
|Megalonema Eigenmann, 1912||54||
|Hemisorubim Bleeker, 1862||56||
|Pseudoplatystoma Bleeker, 1862||56||
|Zungaro Bleeker, 1858||56||
|Sorubim Cuvier, 1829||56||
|Brachyplatystoma Bleeker, 1862||56||
|Steindachneridion Eigenmann & Eigenmann, 1919||56||
|Phractocephalus Agassiz, 1829||56||Present data|
Six specimens of P. hemioliopterus from Amazon Basin/Brazil maintained in the fishing farm of the Universidade Estadual de Londrina were studied cytogenetically. The chromosome preparations were obtained from lymphocyte culture according to
The family Pimelodidae is composed of 109 valid species (Eschmeyer and Fong 2016), but only 27 species have been analyzed cytogenetically (
The diploid number (2n = 56) and karyotype constitution, 16m, 20sm, 6st, 14a (FN = 98) of P. hemioliopterus is reported for the first time (Fig.
Karyotype of Phractocephalus hemioliopterus. Conventional Giemsa staining. Scale bar: 5 µm.
As stated below, diploid number 56 with high fundamental number, NORs located at the terminal position on the short arm of an acrocentric chromosome pair (23th), coincident with positive C-bands (Fig.
The data obtained with CMA3 indicate that the Ag-NORs of P. hemioliopterus are rich in GC pairs (Fig.
Metaphases of Phractocephalus hemioliopterus a AgNO3 staining b CMA3 banding c FISH with 18S rDNA probe and d FISH with 5S rDNA probe. Arrows indicate the NOR-bearing chromosomes and arrowheads indicate the chromosome pair with 5S rDNA.
Heterochromatin distribution revealed by C-banding was evidenced on telomeric regions of some chromosomes, one pair with bitelomeric bands and in the secondary constriction on the short arm of NOR bearing pair (Fig.
Somatic metaphase of Phractocephalus hemioliopterus after C-banding. Arrowheads indicate the chromosome pair with interstitial heterochromatin; arrows indicate the NOR-bearing chromosome and asterisks indicate the chromosomes with heterochromatin blocks in both terminal regions.
Taking into consideration the findings described previously, the present work is the first to provide cytogenetic information about P. hemioliopterus
The cytogenetic description of P. hemioliopterus allowed the karyotypic characterization and the comparison of certain cytogenetic features shared in general with other Pimelodidae, however, some of these traits distinguish the “Sorubiminae group”, suggesting that this species could be integrated into the branch of the great catfishes.