Ernesto Ron

Discrimination of Shark species by simple PCR of 5S rDNA repeats

Sharks are suffering from intensive exploitation by worldwide fisheries leading to a severe decline in several populations in the last decades. The lack of biological data on a species-specific basis, associated with a k-strategist life history make it difficult to correctly manage and conserve these animals. The aim of the present study was to develop a DNA-based procedure to discriminate shark species by means of a rapid, low cost and easily applicable PCR analysis based on 5S rDNA repeat units amplification, in order to contribute conservation management of these animals. The generated agarose electrophoresis band patterns allowed to unequivocally distinguish eight shark species. The data showed for the first time that a simple PCR is able to discriminate elasmobranch species. The described 5S rDNA PCR approach generated species-specific genetic markers that should find broad application in fishery management and trade of sharks and their subproducts.

Extensive polymorphism and chromosomal characteristics of ribosomal DNA in the characid fish Triportheus venezuelensis (Characiformes, Characidae)

The karyotype and chromosomal characteristics of the characid fish Triportheus venezuelensis were investigated using differential staining techniques (C-banding, Ag-NOR staining) and fluorescent in situ hybridization (FISH) with an 18S rDNA probe. The diploid chromosome number (2n = 52), karyotype composition and sex chromosome determination system of the ZZ/ZW type were the same as previously described in other species of the genus Triportheus. However, extensive variation regarding nucleolus organizer regions (NOR) different from other species was observed. 18S rDNA sequences were distributed on nine chromosome pairs, but the number of chromosomes with Ag-NORs was usually lower, reaching a maximum of four chromosomes. When sequential staining experiments were performed, it was demonstrated that: 1.) active NORs usually corresponded to segments with 18S rDNA genes identified in FISH experiments; 2.) several 18S rDNA sequences were not silver-stained, suggesting that they do not correspond to active NORs; and 3.) some chromosomes with silver-stained regions did not display any 18S rDNA signals. These findings characterize an extensive polymorphism associated with the NOR-bearing chromosomes of T. venezuelensis and emphasize the importance of combining traditional and molecular techniques in chromosome studies.

Cytogenetic characterization of hybrids offspring between Colossoma macropomum (Cuvier, 1818) and Piaractus brachypomus (Cuvier, 1817) from Caicara del Orinoco, Venezuela

Abstract Conventional karyotype and nucleolar organizer regions (NORs) of C. macropomum x P. brachypomus hybrids and parental species are reported. A modal diploid number of 54 chromosomes and a fundamental number (NF) of 108 were found for C. macropomum, P. brachypomus and their hybrids. P. brachypomus shows a pair of silver stained chromosomes, while cells with three and four Ag-NOR bearing chromosomes were observed in C. macropomum. The hybrids consistently presented cells with a single metacentric Ag-NOR bearing chromosome and cells with three Ag-NOR bearing chromosomes. The FISH technique was employed to localize 18S rDNA in the chromosomes of the parentals and the hybrids. In P. brachypomus the FITC signals appeared in the SM pair as when stained with silver salts. In C. macropomum the signals were evidenced in six chromosomes. In the hybrids, as expected, the FITC dots were observed in four chromosomes. All the techniques employed in the present work represent good tools to identify the parentals and distinguish them of the hybrids.

Cytogenetic characterization of the silverside fish Odontesthes regia (Humboldt, 1833) (Teleostei: Atheriniformes: Atherinopsidae) from Iquique, Chile

Este trabajo describe el cariotipo de Odonthestes regia, por medio de tincion Giemsa, bandeo C, para revelar la distribucion de la heterocromatina constitutiva, y por medio de tincion con nitrato de plata e hibridacion fluorescente in situ (FISH), para localizar genes ribosomales (rADN). El recuento modal cromosomico diploide en la especie fue de 2n = 48. El cariotipo esta compuesto por un par submetacentrico (par 1), 16 pares subtelocentricos (pares 2 al 17) y 7 pares acrocentricos (pares 18 al 24). Con excepcion del par 1, no fue posible clasificar con exactitud a los cromosomas homologos, ya que las diferencias en el tamano fueron muy pequenas entre pares adyacentes. La distribucion de la heterocromatina por bandeo C permitio aparear a la mayoria de los cromosomas de la serie subtelocentrica. La tincion con plata de preparaciones metafasicas permitio la identificacion de las regiones organizadoras del nucleolo (Ag-RON) en el par 1. Los experimentos FISH mostraron que las secuencias ADNr 18S estaban localizadas, como era de esperar, en el mismo par cromosomico identificado como los portadores de Ag-RON.