A total of 24 digenean species belonging to 10 distinct families (Derogenidae, Faustulidae, Fellodistomidae, Gyliauchenidae, Hemiuridae, Lepocreadiidae, Mesometridae, Monorchiidae, Opecoelidae and Zoogonidae) were recorded in sparid fishes from Bizerte Lagoon (northern Tunisia). The diversity of the digenean fauna of sparid fishes from this locality is compared to that recorded from the Gulf of Tunis. Prodistomum polonii, not detected before, was found in Sarpa salpa. Aphallus rubalo, Derogenes latus, Holorchis micracanthum and Pachycreadium carnosum previously recorded from sparid fishes on the Tunisian coasts were absent during this study. Allopodocotyle pedicellata, Lepocreadium pegorchis, L. album, Proctoeces maculatus, Magnibursatus bartolii and Macvicaria maillardi were reported in hosts not previously reported for the Gulf of Tunis. Generally, prevalence was higher in fishes from Bizerte Lagoon but abundance and mean intensity were higher in Gulf of Tunis. Except for Lithognathus mormyrus, Sarpa salpa and Sparus aurata from Bizerte Lagoon, which show higher digenean diversity, the other sparid fishes have a lower diversity compared to those from Gulf of Tunis. The species richness of digeneans in B. boops was the same in the two areas studied.

Anguillicola crassus, parasite nematode of the European eel Anguilla anguilla, was recorded for the first time in Tunisia (1999) in the Ichkeul lagoon. Its distribution has since spread toward Bizerte and Ghar El Melh lagoons. The monthly epidemiological survey reveals that A. crassus exists throughout the year in the Ichkeul lagoon. In this lagoon, its prevalence is low in winter (12% in December), with a marked increases in the spring reaching a maximum in March (35%), before it starts to decrease in summer with a minimum in July (4.35%), which in turn is followed by a pronounced new rise in autumn (30% in November). However, mean intensity values do not show such a marked variation. The majority of the values are between 1 and 1.5 parasites per host. In the Bizerte and Ghar El Melh lagoons, the presence of this nematode is limited only to one to three months. Investigations in the Tunis lagoon did not reveal until now the presence of A. crassus. It has been observed that the length of the eel influences the prevalence values: A. crassus becomes less common if the length of the eel increases. Comparatively with the global epidemiological values of A. crassus signalled subsequently (1999) in the Ichkeul lagoon, we note that the present values record a clean increase. To cite this article: L.

Cercaria lata (Digenea, Faustulidae), discovered by Lespés (1857) in Tapes decussata (L.) in the basin of Arcachon, was found for the first time, from the eastern Mediterranean, in the same lamellibranch from Tunisia (Bizerte and Tunis lagoons and Gulf of Gabes). These cercariae develop in daughter sporocysts, which develop in mother sporocysts in the gonads. Daughter sporocysts are observed in the gonads and sometimes in the digestive gland. A redescription and the behaviour of the naturally emerging cercariae and spatio-temporal distribution of the sporocysts are reported. A comparative study using multivariate analyses associated with morphology, biology and seasonality confirm the distinctness of Cercaria lata and the cercaria of Cercaria pectinata from Donax trunculus.

Shell disturbances and soft tissues butyltin burden were investigated in commercial bivalves Lithophaga lithophaga, Mytilus galloprovincialis, Solen marginatus and Crassostrea gigas from the Bizerta lagoon. Shell disturbances were found in all bivalves, being scarce in S. marginatus. In the internal valve of L. lithophaga, burrowing annelids and sipunculids living inside galleries were observed, while in the external valve, brown-blackish or white stains were found. In M. galloprovincialis, a yellowish mass located at the shell anterior side was found fixed firmly to the pearly layer by a hard brownish structure covering some annelid elliptic eggs. In the internal shell layer of some specimens collected in April, embryos belonging to tubiculous annelids at various developmental stages were observed. In C. gigas, shell thickening was revealed in some specimens corresponding to white doughy deposits at the internal valve and between shell layers. In S. marginatus, only one specimen showing a cavity at the posterior site was found. Total butyltin concentrations in the studied bivalves varied between 30 and 245 ng/g dry weight with tributyltin (TBT) being the predominant compound. The highest concentration was recorded in L. lithophaga collected from the Bizerta Bay and the lowest concentration in S. marginatus from Maghraoua. This study provided baseline data that could serve for long-term monitoring of TBT pollution in Tunisia, since legislation to reduce the use of TBT-based antifouling paints has not been introduced yet.

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