A. Cau

This paper explores structure and spatial distribution of fish assemblages in an area of the central-western Mediterranean Sea (south Sardinian deep-waters) at depths between 546 and 1598m. A total of 67 species (12 chondrichthyes and 55 teleosteans) were sampled. Multivariate analysis showed a clear pattern of zonation. Three main assemblages were identified within the vertical range investigated: the first situated in the shallower area between 546 and 699m, the second group between 720 and 1099m, and the third between 1145 and 1598m. Abundance values declined with increasing depth. Highest biomass values were found at depths of 720-1099m with the presence of larger species such as Galeus melastomus, Mora moro, Trachyrhynchus scabrus and Alepocephalus rostratus. Species richness decreased with depth. The deepest bottoms of the central-western Mediterranean Sea shelter an ichthyofauna dominated by small to medium-sized species living in a food-scarce environment in which some large mobile fishes are widesprea

We have studied fixed chromosomes and purified DNA of Anguilla anguilla L. after digestion with HaeIII, AluI, MboI, and DdeI restriction endonucleases. Our data demonstrated (i) confirmation of the heteromorphic nature of NORs, (ii) absence of detectable sex chromosomes, and (iii) presence of discrete intercalary domains in this species. Our data also permitted us to hypothesize the existence of highly repetitive DNAs, localized in specific heterochromatic regions of A. anguilla chromosomes.Key words: fish, chromosomes, DNA, restriction enzymes.