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Morphometric characters of the white seabream Diplodus sargus (Linnaeus 1758) were compared among samples collected from six marine and lagoon sites along the Tunisian coast to elucidate the impact of the geographical barrier of the Siculo-Tunisian Strait and/or the lagoon environment in the morphological variation among the Tunisian white seabream population. Two morphometric descriptors (twenty-five Truss elements and six traditional measurements) were used to study the pattern of this morphological variation. Univariate analysis of variance revealed significant differences (P < 0.001) for both traditional and Truss variables. Multivariate analysis using the two morphometric descriptors detected a clear variation in the body shape between D. sargus populations along the Tunisian coast. All these analyses showed the distinctness of the sample from El Biban lagoon compared to the remaining ones. This discrimination was due to the head and the peduncle of the studied fish. Varying degrees of differences were also observed between northern and southern samples, and between the lagoon and the marine samples. The morphologi- cal variations of the head explain also the discrimination between the different lagoons samples. Observed morphological heterogeneity seems to be related to the impact of ecological factors.
Two specimens of the west African goatfish, Pseudupeneus prayensis (Cuvier, 1829), were found for the first time off the Tunisian coast, in northern area. They constituted the third Mediterranean record of this fish. Both specimens were studied and described, and some biological observations were reported. Same taxonomic characters were concomitantly determined on two west African goatfish caught off the coast of Senegal, for comparison. The occurrence of Pseudupeneus prayensis in the area and the Mediterranean Sea is discussed and commented.
Background. The red mullet, Mullus barbatus L., is abundantly captured and targeted throughout the year in Tunisian waters but not all aspects of its biology have been studied well. One of them—the feeding behaviour of this fish may be important for stock assessment, ecosystem modelling, and understanding mechanism and processes which structure and influence the fish assemblages. The aim of this paper is to describe the diet of specimens from the northern coast of Tunisia, to analyse seasonal variations in its composition and to delineate feeding intensity in relation to sex and size. Materials and methods. Red mullet were sampled from different landing sites along the northern Tunisian coast and the Gulf of Tunis. Random samples were taken from both commercial and demersal trawlers from January to December 2005. A total of 472 specimens were examined following the commonly accepted procedures. The following parameters were analysed: vacuity index, percentage frequency of occurrence, percentage numerical abundance, percentage gravimetric composition, and index of relative importance. The trophic level for any consumer species was calculated, for total sample, but also in related to size, sex, and season. Results. Mullus barbatus mainly fed on crustaceans and polychaetes. According to the classification of fishes in functional groups based on their TROPH red mullet is an omnivorous feeder, animal species being preferential preys. Basing on data assembled by Stergiou and Karpouzi for the Mediterranean ichthyofauna, the estimated trophic levels for the red mullet ranged between 2.79 and 3.57 units. Such within-species differences in trophic levels might reflect the combined effect of the following factors: area, year, length structure, and differential fishing pressure between years and/or areas, because fishing removes the largest individuals of a species, which generally have higher trophic levels. Conclusion. The red mullet is not only omnivorous, but also opportunistic feeder with trophic level related to body size, season, geographic area and fishing pressure.
Investigations conducted off the northern Tunisian coast (central Mediterranean) allowed the authors to collect a male of the unicorn leatherjacket filefish, Aluterus monoceros (L.). The specimen is described in this note, including morphometric measurements and meristic counts. This finding constitutes the first record of A. monoceros off the Tunisian coast and the second record for the Mediterranean Sea. The occurrence of this species in the area and the Mediterranean Sea is discussed and commented.
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