Maria Vallisneri

Comparative Analysis of a Mitochondrial DNA Control Region Fragment Amplified from Three Adriatic Flatfish Species and Molecular Phylogenesis of Pleuronectiformes

Abstract The 5′-end of the mitochondrial control region of three Pleuronectiformes from the Adriatic Sea, Platichthys flesus italicus (Adriatic flounder), Solea vulgaris (common sole), and Solea kleini (Kleins sole), was sequenced and compared with that of six other flatfish species from the families Pleuronectidae and Bothidae. The sequence structures of all flatfishes appear very similar and consist of alternate short segments with low, medium, and high rates of nucleotide substitution. Four conserved 19-bp repeats occur at the beginning of the European and Adriatic flounder sequences. The common occurrence of tandem arrays in fish control regions could be related to a stable secondary structure. Molecular phylogenetic relationships among Pleuronectiformes agree well with previous morphologic data at all taxonomic levels. Molecular analyses could therefore contribute to resolving phylogenetic and taxonomic debates within the Pleuronectiformes.

Mitochondrial DNA variation, phylogenetic relationships, and evolution of four mediterranean genera of soles (soleidae, pleuronectiformes).

To increase knowledge about the systematics and evolution of Mediterranean soles, we assessed mitochondrial DNA variation, molecular phylogeny, and evolution in eight species from the genera Solea, Microchirus, Monochirus, and Buglossidium by large ribosomal subunit (16S) and cytochrome b (cytb) sequence analysis. Relevant molecular features are the great variation of base composition among species at the third codon in cytb and the heterogeneity of the nucleotide substitution rate. Phylogenies recovered using 16S nucleotide and cytb amino acid sequences agree with those based on morphology in assessing monophyly of Solea species and ancestry of Buglossidium luteum, but they are against the intergeneric differentiation of Microchirus and Monochirus. Conversely, phylogenetic trees based on cytb nucleotide sequences yielded relationships among taxa regardless of their evolutionary histories. The incongruities between morphological and molecular issues suggest the need for reassessing the systematic value of some morphological characters. Approximate estimates of the divergence time of Mediterranean soleid lineages range from 40 to 13 Mya (Oligocene–Miocene), indicating an ancient origin for the group.

Feeding strategy and ontogenetic changes in diet of gurnards (Teleostea: Scorpaeniformes: Triglidae) from the Adriatic Sea

Abstract A multi-specific approach in fish diet studies provides insight into the complexity of trophic interactions in marine communities. The feeding habits of three gurnard species, Aspitrigla cuculus, Chelidonichthys lucerna and Eutrigla gurnardus (Scorpaeniformes: Triglidae), from the north-middle Adriatic Sea were studied to evaluate prey-resource partitioning amongst species and within species, comparing juveniles’ and adults’ diet for each gurnard species. A total of 1818 specimens (390 A. cuculus, 973 C. lucerna, 455 E. gurnardus) were collected by bottom trawling and they were assigned to size classes (juveniles or adults) on the basis of macroscopic evaluation of the gonads. Stomach contents were analysed. A common dietary preference for Crustacea was found in all species and size classes considered. Nevertheless, gurnards showed distinct feeding behaviour: C. lucerna and E. gurnardus were generalist-opportunistic predators, showing a varied diet based on epi-benthic, bentho-pelagic and necto-benthic preys belonging to different taxa such as Teleostei and Mollusca, while A. cuculus may be considered a specialist feeder, feeding almost exclusively on necto-benthic invertebrates. Morisita’s index calculated for critical size classes (juveniles and adults) pointed out differences. At the inter-specific level, possible dietary competition between A. cuculus and E. gurnardus (C > 0.65) was found for all size classes combined, due to the prey abundance of Lophogaster typicus (Crustacea: Mysida). At the intra-specific level, high diet overlap was found between juveniles and adults of C. cuculus (C = 0.98) and between juveniles and adults of E. gurnardus (C > 0.84). In contrast, C. lucerna did not compete with increasing body size (C < 0.20), showing a clear change from crustaceans to fish in its diet preferences. The possibility that A. cuculus and E. gurnardus may compete for the same prey resources while C. lucerna shows food resource partitioning is discussed. Better understanding of the ecology of these coexisting predators should lead to improved conservation and improved fisheries management.

Histological changes in the ovary of Palaemon serratus (Crustacea, Decapoda) from the North Adriatic Sea

Summary Despite its considerable commercial importance, the ovarian maturation of the prawn Palaemon serratus (Crustacea, Decapoda) has been scarcely studied, especially in the marine habitats of Italian waters. For the purpose of the present study female samples were collected in the North Adriatic Sea for one year. Gonadal tissue sections were prepared using current histological techniques. The ovaries feature a “proliferative centre” from which oocytes maturing in a centrifugal direction branch out. Oocyte (n = 554) size in μm was determined at various stages of development using a semiautomatic computerized imaging scanner. Five cohorts at around 60, 120, 180, 240, 700 μm of diameter were recorded in oocyte distribution frequency during ovary maturation (spring-summer). Only two cohorts at around 60 and 120 μm were observed in oocyte distribution frequency in the immature ovary (autumn-winter). The goal of this study was to provide a preliminary characterisation of the histological structure of the ovary throughout the reproductive cycle. Although P. serratus is a commercially valuable natural resource and has potential for artificial culture, little is known as to the reproductive biology of this species and, unless remedied, this could hinder its successful rearing.