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Cytogenetic studies were performed in four species of two scorpaeniform teleost families: Scorpaenidae and Triglidae. The karyotypes of Trigla lucerna, Trigloporus lastoviza (Triglidae), Scorpaena porcus and S. notata (Scorpaenidae) were analysed using various banding methods and in situ hybridization with a telomeric probe. In the two Scorpaena species, modest morphological divergence corresponded to considerable karyotype reorganization, while in the two Triglidae substantial phenotypical divergence corresponded to limited chromosomal changes. These data stress the need for a taxonomical re-evaluation of these teleosts based on characters independent of morphology.

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Chromosomal location of major ribosomal genes (18S–5.8S–28S rDNA) and (TTAGGG)n telomeric sequences has been investigated for the first time in pipefish (Syngnathidae) by application of fluorescence in situ hybridization (FISH). Two species were studied: Nerophis ophidion (L.) (2n karyotype = 58 metacentric, submetacentric and subtelocentric chromosomes)and Syngnathus abaster Risso (2n karyotype =44 acrocentric chromosomes) (Vitturi et al. 1998). The results indicate that in both pipefishes intraspecific numerical variation of ribosomal sites is more conspicuous than previously detected (Vitturi et al. 1998). (TTAGGG)n FISH showed a regular hybridization pattern in S. abaster, while in N. ophidion it gave unexpected enlarged hybridization signals in the terminal region of either two or five chromosomes, where telomeric sequences were interspersed throughout nucleolus organizer regions NORs (interstitial telomeric sites, ITS). Diversification of ribosomal and telomeric repeats in the karyotype of the two species confirms the hypothesis that the genera Nerophis and Syngnathus have undergone two different pathways of karyotypic evolution. The teleostean family Syngnathidae (pipefish and seahorses)includes 277 species, of which 11 inhabit the Mediterranean Sea and belong to the genera Nerophis (two species), Hippocampus (two species), Minyichthys (one species) and Syngnathus (six species) (FishBase 2005). Owing to the difficulty in obtaining high-quality chromosome preparations, cytogenetic data on syngnathids are scanty, referring in literature only to five Mediterranean species (two seahorses and three pipefishes), and are restricted to only a few aspects, including diploid chromosome number, karyotypic macrostructure, location of active NORs by silver staining, and genome size (Vitturi et al. 1998). With regard to NOR location, staining with silver nitrate and the fluorochrome chromomycin A3 (CMA3) has been widely applied to metaphase plates of both vertebrates and invertebrates to detect number and position of active NORs and GC-rich NORs, respectively (Sumner 1990, and references therein). However, both methods have proven to be inadequate in unequivocally characterizing the ribosomal pattern (active and inactive rDNA genes) in the karyotype of several species. It has been shown that molecular techniques provide additional opportunities for animal cytogenetics.Gasteroisteiformes and its family Syngnathidae. In this note we report the first attempt to apply FISH to pipefish chromosomes.

An unexpected result arising from a previous characterization of the scarab beetle Bubas bison (Coleoptera: Scarabaeidae) heterochromatin was its unusual homogeneous reaction to different staining methods. In particular, silver stainability of heterochromatic ends of all chromosomes prevented identification of the number of rDNA transcriptionally active regions. Data formerly obtained using silver impregnation (Ag-NOR), C- G- and DAPI banding are here improved and completed by application of CMA3 staining and rDNA FISH with the aim to investigate heterochromatin base composition and locate rDNA regions with respect to NOR-associated heterochromatin. Our results show that B. bison has a high amount of heterochromatin (almost 50%) and that - as revealed by rDNA FISH - major rRNA genes are spread over the heterochromatic telomeric regions of eight chromosomes, thus suggesting that only a portion, although consistent, of total heterochromatin is associated with ribosomal clusters. Moreover, DAPI-positive (AT-specific) and CMA3-negative (GC-specific) reactions of heterochromatic DNA confirm its AT-rich composition. Finally, possible explanations for the bright DAPI-fluorescence of both heterochromatin and rDNA sequences are discussed.

A cytogenetic study was carried out on the chromosomes and nuclear DNA contents of the land snails Cantareus aspersus and C. mazzullii (Gastropoda: Pulmonata). Chromosomes were studied using Giemsa staining, banding methods and fluorescent in situ hybridization (FISH) with three repetitive DNA probes [18S rDNA, (GATA)n and (TTAGGG)n]. Results were very similar in the two species both showing (1) 54 bi-armed chromosomes [submetacentrics (SM) + metacentrics (M) + subtelocentrics (ST)]; (2) 10 terminal NORs after sequential application of rDNA FISH and silver staining; (3) uniform DNA fluorescence with CMA3 and DAPI staining and (4) genomic composition considerably enriched both in highly- and moderately-repeated DNAs. The telomeric (TTAGGG)n sequence hybridized with the termini of all of the chromosomes in the two species. In spite of their apparent karyological uniformity, flow cytometry DNA assays showed that C. aspersus and C. mazzullii are characterized by different nuclear DNA content (C values are 3.58 and 3.08 pg, respectively) and slightly different base composition in their genomes. Present data on GS and AT% in C. mazzullii and C. aspersus confirm the trend toward high GS values and GC percentages among land snails.

The chromosomes of the Mediterranean killifish, Aphanius fasciatus from two populations, the Lagoon of Venice (LV, 15 specimens) and the Lagoon ‘Stagnone di Marsala’ (Sicily) (SM, 48 specimens), have been investigated using conventional Ag-staining and fluorescent in situ hybridization (FISH) with 18S rDNA probe. The two methods revealed variation in the number of major rDNA sites ranging from 8 to 14 (LV) and from 1 to 4 (SM) per individual. The fact that each individual possessed its own number of sites implies that observed variation was structural. Moreover, overlapping of silver staining and FISH patterns demonstrated that all ribosomal genes were transcriptionally active in each specimen.

Spermatocyte chromosomes of Melarhaphe neritoides (Mollusca, Prosobranchia, Caenogastropoda) were studied using fluorescent in situhybridization (FISH) with four repetitive DNA probes (18S rDNA, 5S rDNA, (TTAGGG)n and (GATA)n). Single-colour FISH consistently mapped one chromosome pair per spread using either 18S or 5S rDNA as probes. The telomeric sequence (TTAGGG)n hybridized with termini of all chromosomes whereas the (GATA)n probe did not label any areas. Simultaneous 18S-5S rDNA and 18S-(TTAGGG)n FISH demonstrated that repeated units of the three multicopy families are closely associated on the same chromosome pair.

Despite the interest of several authors, the karyotype of the labrid C. julis is still debated and in particular the presence of sex-chromosomes is still contradictory. In order to analyze the karyotype organization of C. julis we have performed an analysis with classical and molecular cytogenetic techniques. Our results after silver-, CMA3- and DAPI-staining, C-banding and fluorescent in situ hybridization (FISH) using 28S rDNA, 5S rDNA, and telomeric repeat (TTAGGG)n, as probes allowed us to characterize the chromosomal location of several repetitive DNAs of C. julis. Finally, regardless of the technique used, no difference in the chromosome complement was found between males and females.