Karyotype differentiation between two species of carangid fishes, genus Trachurus (Perciformes: Carangidae)

A karyological study of Trachurus trachurus and T. mediterraneus (Perciformes: Carangidae) was conducted by standard, fluorochrome staining (CMA ₃, mithramycin, quinacrine mustard, DAPI), C-, Ag-NOR, and Alu-I banding methods. The karyotypes of both species consisted of 2n = 48 chromosomes, but of different FN: T. trachurus possessed a chromosome complement of 2 metacentric and 46 acrocentric elements, fundamental number (FN) = 50 and T. mediterraneus, a chromosome complement of 4 metacentric, 4 submetacentric, 14 subtelocentric and 26 acrocentric chromosomes, FN = 70. In neither of the two taxa investigated were heteromorphic sex chromosomes observed. The nucleolar organizer region was interstitially located on the long arm of the 1st pair of chromosomes in both species, intermediate in T. mediterraneus and subterminal in T. trachurus. Constitutive heterochromatin was found in nearly all centromeric and telomeric regions in T. trachurus; in T. mediterraneus it formed less intense telomeric and centromeric bands and thin interstitial bands on eight chromosome pairs. In addition, the C-positive material reacted differently to the digestion with endonuclease Alu-I in the two species. The results are discussed and compared with karyological data known for other species of Carangidae.