The anatomy and the histology of the digestive tract of young and adult sea-bream is described from studies using light and scanning electron microscopy. The dentition in the juvenile (25-30 mm long) comprises all canine-like teeth. to which plate teeth and transition elements are added in the adult.The oesophagus shows a multi-layered mucosa in the upper part, and single-layered regions in the lower part. The multi-layered regions are formed by epithelial cells, mucus-secreting cells and by cells rich with eosinophilic granules.The Y-shaped stomach, clearly distinguishable. has a single-layered columnar epithelium under which, in the cardiac and fundic portion, gastric glands, comprised of all similar cells, are present. The pyloric region is characterized by four caeca, to the base ofwhich the ductus pancreaticus and the ductus hepaticus discharge.The pancreas is composed of small masses spread along the upper intestine; in the adult, pancreatic infiltrations can be seen in the liver.The intestine is short (relative length 0.5-0.6). The intestine epithelium consists of columnar cells intercalated with mucus-secretingcells. A funnel-like valve marks the passage to the intestine terminal region, characterized by a mucosa of cells with an abundance of vacuoles full of eosinophilic granules.

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This study was carried out to investigate the genetic variability and the population genetics of Sparus auratus. In fact, despite its importance in Mediterranean fisheries and aquaculture, very little it is known concerning its population structure. Samples of wild gilthead sea bream were collected in seven different localities along the Mediterranean and Atlantic coasts and were genetically characterized by means of microsatellite markers. Genotyping at four microsatellite loci revealed high polymorphism (7-38 alleles/locus) and expected heterozygosities, which ranged from 0.80 to 0.85. A slight but significant population structure was found ( F ST = 0.010). In fact, at least three populations of gilthead sea bream within the Western Mediterranean Sea were identified (Sardinian Sea, Sardinian Channel and Central Tyrrhenian Sea), which are also genetically differentiated from those of the Atlantic Ocean and the Adriatic Sea.

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The family Mugilidae (Pisces, Mugiliformes) includes species which are present in all tropical and temperate regions. Six species, Chelon labrosus, Mugil cephalus, Liza aurata, L. ramada, L. saliens, Oedalechilus labeo, are commonly found in the Mediterranean. These species have been widely studied through morphological, biochemical, and molecular markers. However, their phylogenetic relationships, and therefore the assumed monophyly of Liza species, still remain unclear: To further investigate this topic, gene-enzyme systems and sequences of the partial 16S rRNA mitochondrial gene were analyzed in Italian samples of all six Mediterranean species. The phylogenetic reconstructions indicated M. cephalus as being the most divergent species and the existence of a main cluster including all the Mediterranean species of Liza and C. labrosus. The parametric bootstrap approach adopted to test alternative phylogenetic hypotheses indicated that the Mediterranean species of Liza do not form a monophyletic group exclusive of Chelon.

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The big-scale sand smelt Atherina boyeri lives in fresh water, brackish water and sea water of the western Atlantic Ocean and Mediterranean Sea. Previous studies concerning distribution, biometric characters and genetic molecular markers have suggested the possible existence of two or even three different groups or species of sand smelt, one 'lagoon' type and one (or twopunctuated and non-punctuated on the flanks) 'marine' type. In this study, the presence and the localization of an insertion was described, c. 200 bp in length, in the mtDNA of the lagoon and marine punctuated specimens of A. boyeri and its absence in the marine non-punctuated specimens, as well as in other two congeneric species, Atherina hepsetus and Atherina presbyter, and in the atheriniform Menidia menidia. The intergenic spacer is located between the tRNA Glu and cytochrome b (cyt b) genes and shares a c. 50% sequence similarity with cyt b. The distribution and the features of the intergenic spacer suggest that it might have originated from an event of gene duplication, which involved the cyt b gene (or, more likely, a part of it) and which took place in the common ancestor of the lagoon and the marine punctuated specimens. The data obtained therefore support the hypothesis of the existence of three cryptic and, or sibling species within the A. boyeri taxon and provide a genetic molecular marker to distinguish them.