Stock discrimination of Chelidonichthys obscurus (Triglidae) in the central Mediterranean Sea using morphometric analysis and parasite markers.

Assessing fish stocks has important implications for fisheries management and conservation biology. Gurnards are marine demersal fish that commonly occur in the Mediterranean, but their population in this region remains to be quantified. This study examines the population structure of the longfin gurnard Chelidonichthys obscurus (Walbaum, 1792) in waters off eastern Tunisia, using morphometry and parasite assemblages. A total of 134 fish are investigated from two studied zones - the Gulf of Hammamet and the Gulf of Gabès. Discriminant analysis is used to compare gurnard populations in the two studied zones using 13 morphometric characters and the infection parameters of seven parasites. Morphometric analysis reveals strong spatial variations between the studied zones, providing evidence for the existence of an ecological differentiation along the eastern Tunisian coast. Mahalanobis distances show that body height, pectoral fin length and first dorsal fin length are the most salient morphometric characters for determining the position of samples from the Gulf of Gabès. The effectiveness of using parasites to study longfin gurnard stocks is uncertain. The use of short-lived parasites as biological tags is questionable, at least in the present case. Future research, based on complementary approaches such as otolith microchemistry and genetics, may improve our understanding of the global stock structure of longfin gurnard to suitably inform regional organizations involved in fisheries management.

A new genus and three new species of Anthocephaliidae (Cestoda, Rhinebothriidea) from the round fantail stingray, Taeniurops grabata (Chondrichthyes, Dasyatidae) from the Mediterranean Sea and Atlantic Ocean.

The spiral intestines of a total of 16 round fantail stingrays Taeniurops grabata from the Mediterranean Sea off Tunisia were examined for cestodes. A new genus is erected in the Anthocephaliidae (Rhinebothridea) as Alveobothrium gen. n., with Alveobothrium grabatum sp. n. as its type species; the new genus differs from the other genera in the order in that its members possess bothridia with an apical sucker, marginal loculi and multiple staggered rows of facial loculi. Alveobothrium zarzisense sp. n. is also described. The species differ in the number of marginal loculi and in proglotid anatomy. Another anthocephaliid belonging to the genus Anthocephalum is also described from T. grabata. Anthocephalum jeancadenati sp. n. is most similar to A. alicae and A. michaeli, but differs in size of terminal proglottid and number of proglottids. All these new species are also found in formalin-preserved cestodes from T. grabata collected at Gorée Island (Senegal) between 1946 and 1954 by the French ichthyologist J. Cadenat and conserved in the personal collection of the late L. Euzet. The presence of the same rhinebothriideans species parasitizing T. grabata in both the Mediterranean (Tunisia) and the eastern Atlantic (Senegal) is discussed.

Helminth parasites of the chub mackerel Scomber colias off the Tunisian coast and their use in stock discrimination.

Nine helminth parasites were used as biological tags to discriminate diverse areas of Scomber colias Gmelin, 1789. During three seasons, a total of 369 fish were examined in four zones off the Tunisian coast, including Bizerte in the north, Kelibia and Mahdia in the centre and Zarzis in the south. Discriminant analyses were used to identify distinct areas of S. colias. Fish from Bizerte were grouped as one area and were correlated negatively with the monogenean Grubea cochlear and the digenean Lecithocladium excisum. Specimens from Kelibia and Mahdia were grouped together and were characterized by the ectoparasite Pseudokuhnia minor and by endoparasites Prodistomum orientalis, Monascus filiformis and anisakid larvae. Fish from Zarzis were grouped as one area and were positively correlated with the monogenean G. cochlear and the digenean L. excisum. These results were corroborated by comparing the prevalence and mean abundance of parasites among zones. Results of other discriminant analyses used for the classification of S. colias between localities after pooling specimens from the central areas of Kelibia and Mahdia also allowed the identification of three distinct areas: one in the north, correlated negatively with G. cochlear and L. excisum; one in the centre, characterized by P. minor, P. orientalis, M. filiformis and anisakid larvae; and one in the south, from Zarzis, characterized by G. cochlear and L. excisum. Results of comparisons of infection parameters between seasons and those of seasonal discrminant analyses showed a seasonal stability of communities from the northern and the southern areas. Specimens from the central regions showed variability between seasons, suggesting migratory movements.

Lamellodiscus euzeti n. sp. (Monogenea:Diplectanidae), a parasite from Dentex canariensis and D. gibbosus (Teleostei:Sparidae) in the Atlantic Ocean and Mediterranean Sea.

Lamellodiscus euzeti n. sp. (Monogenea:Diplectanidae) is described from the gills of two sparid fishes, Dentex canariensis (Steindachner) off Senegal and Ivory Coast and D. gibbosus (Rafinesque) off Senegal and Tunisia. The new species belongs to the "ignoratus" group, characterized by a lamellodisc with complete lamellae, a "lyre" shaped male copulatory organ type, and the "ignoratus" sensu stricto subgroup, characterized by a haptor with simple lateral dorsal bars. Lamellodiscus euzeti n. sp can be distinguished from all the congeneric species of the "ignoratus" subgroup by the presence of a prominent protuberance at the base of the curved part of the simple piece of the male copulatory organ (MCO), a large bulb at the base of the bifurcated piece of the MCO and the presence of 5-6 spines in the distal portion of the axial branch of the bifurcated piece of the MCO. Specificity and biogeography of Lamellodiscus species from sparid fishes are discussed.