Nucleolar organizer (NOR) location and cytotaxonomic implications in six species of gobiid fishes (Perciformes, Gobiidae)

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Abstract
A karyological study of Adriatic populations of Gobius niger, G. paganellus, G. cobitis, Pomatoschistus minutus, P. marmoratus, and Zosterisessor ophiocephalus (Teleostei, Gobiidae) was conducted by fluorochrome staining lchromomycin A3 (CMA3), mithramycin (MMA), C‐, AgNOR‐and Alu‐I banding methods. The NORs showed three types of location: terminal‐centromeric on one pair of medium‐small chromosomes in G. niger, G. paganellus, P. minutus, and P. marmoratus, terminal on the long arm of chromosome 23 in Z. ophiocephalus; interstitial‐pericentric on the long arm of chromosome 3 in G. cobitis. Except for the two Pomatoschistus, all species had structurally heteromorphic NOR‐bearing chromosomes. The heterochromatin was mainly cen‐tromeric and telomeric. Except for G. niger and G. paganellus, in which only the heterochromatin of chromosome 1 was Alu‐I resistant, the endonuclease Alu‐I produced a C‐band‐like pattern. In G. niger, G. paganellus, and Z. ophiocephalus, the short arm of chromosome 1 showed variable amounts of C‐banded material. In addition, in G. niger the heteromorphic element of chromosome 1 presented a CMA3/MMA and Ag‐positive telomeric region on the short arm. The results obtained are discussed with respect to cytotaxonomic implications and to the features of NORs.