Cytogenetic analysis of Epinephelus marginatus (Pisces : Serranidae), withthe chromosome localization of the 18S and 5S rRNA genes and of the (TTAGGG)(n) telomeric sequence

A cytogenetic analysis was carried out on specimens of Epinephelus marginat us (Lowe, 1834) from three localities in the Mediterranean Sea, to deepen k nowledge of the chromosome complement of the species and identify any possi ble population-specific cytogenetic markers. All specimens had a 2n = 48 ac rocentric karyotype with two Ag-, chromomycin A(3)- and C-positive NORs (nu cleolar organizer regions) in the subcentromeric region of the smallest chr omosome pair. The constitutive heterochromatin was distributed centromerica lly. Except for NORs, neither eu- nor heterochromatin show fluorescence aft er fluorochrome staining, i.e, there is no localized increase of AT- or GC- rich DNA. In all populations, the (TTAGGG)(n), telomeric sequences are rest ricted to the telomeres, and the 18S and the 5S rDNA clusters are located o n different chromosome pairs. In specimens from Sardinia, additional signal s after C-banding, Ag-staining and FISH (fluorescence in situ hybridization ) with 18S rDNA can be observed in the telomeric region of one or two large -sized chromosomes! classified as No. 2. This suggests that additional and variable NORs could be detected in the species in addition to those on the genus-specific, NOR-bearing Chromosome Pair 24.