Influence of season and site location on European cultured sea bass parasites in Corsican fish farms using indicator species analysis (IndVal).

The parasites of 536 European sea bass, Dicentrarchus labrax, were studied between January 2012 and December 2013 in six Corsican fish farms. The indicator value (IndVal) method, which combines measures of fidelity and specificity, has been used in this study. Because of its resilience to changes in abundance, IndVal is a particularly effective tool for ecological bioindicator. The IndVal method showed how season can influence the occurrence of parasite species in cultured sea bass and also identified parasites as bioindicators relative to fish farm location. The combination of specificity and fidelity highlighted several parasite species as significant indicators. A randomization test identified five parasite species as having a significant indicator value for season (the monogenean Diplectanum aequans; the copepods Lernanthropus kroyeri and Caligus minimus; the isopod Ceratothoa oestroides, and the myxosporidian Ceratomyxa labracis). If gills parasites are compared, they can be seen to be indicator species for two different seasons. The only Monogenea species D. aequans had fidelity and specificity more pronounced in winter, whereas both copepod species and the Isopoda revealed highest rates of infestation corresponding with an increase of water temperature. Four species have a significant indicator value for site location (D. aequans, L. kroyeri, C. minimus, and C. oestroides). The fact that the farm 6 was isolated on the east coast of Corsica may not have allowed the parasite to infect other farms. The presence of copepods on a single farm can also be explained according to salinity variations. Data for species composition and infection levels should help to improve the monitoring and management of parasitism in cultured sea bass populations.

Topography and ultrastructure of the tegument of Aphallus tubarium (Rodolphi, 1819) Poche, 1926 (Digenea: Cryptogonimidae), intestinal parasite of the common Dentex dentex (Linnaeus 1758) from Valinco Gulf.

The tegument ultrastructure of the intestinal fluke Aphallus tubarium was studied for the first time with the use of scanning and transmission electron microscopy. New details on morphology were recorded. The ultrastructural study revealed that the tegument of A. tubarium had a syncytial organization with a distal cytoplasm lying over a basal matrix and cytons. The surface of the tegument is covered with pectinate spines arranged quincuncially. As anterior-posterior differences were observed, particular attention was given to spines. Spines decrease in size and density from the anterior part of body to posterior part. Two types of sensory structures were identified, uniciliated and dome-shaped. Type 1 sensory receptors were outgrowths bearing groups of papillae with shorter and rigid apical seta visible on the anterior part of body surface, encircling the worm. Type 2 sensory receptors was dome-shaped papillae devoid of cilia, found mainly around the oral sucker. Diagrams of spines and sensory receptors were made to help in understanding the nature of these structures. Surface morphology may prove to be useful in distinguishing Aphallus spp with other Cryptogonimidae.

Lernanthropus kroyeri (Van Beneden and Hesse 1851) parasitic Copepoda (Siphonostomatoidae, Lernanthropidae) of European cultured sea bass Dicentrarchus labrax (Linnaeus 1758) from Corsica: ecological and morphological study.

Lernanthropus kroyeri (Copepoda, Siphonostomatoida: Lernanthropidae) is a gill parasite found on the European sea bass Dicentrarchus labrax. During a survey of sea bass of Corsican fish farms, we studied the biology of this parasite under culture conditions. We first chose to conduct a scanning electron microscopic study to give additional information about the lifestyle of the parasite. Our examinations made it possible to reveal some unreported superficial structures including details not described previously. Specializations associated with the tegument, in particular, sensory structures and anchoring systems were studied to understand the mechanisms of survival and dispersal of the species. Patterns variation of parasites communities was examined by taking into account environmental factors, such as temperature or salinity, and physiological parameters related to host. The relation between parasites and location of fish was also studied to quantify the importance of site influence on parasite communities. Prevalence and abundances of the infections in different culture systems, fish stocks, and sampling seasons are given. L. kroyeri was significantly present during spring and summer, coinciding with a period of increasing temperature. Significant differences were found grouping data by host size, with higher infection levels in the larger-sized fish.

Sparicotyle chrysophrii (Van Beneden and Hesse 1863) (Monogenea: Polyopisthocotylea) parasite of cultured Gilthead sea bream Sparus aurata (Linnaeus 1758) (Pisces: Teleostei) from Corsica: ecological and morphological study.

Sparicotyle chrysophrii infections were highlighted during a parasitological monitoring carried out on cultured Gilthead sea bream Sparus aurata Linnaeus 1758 from aquaculture sites in Corsica. Factors and biological mechanisms regulating parasites populations, particularly controlling the infestation and survival of monogeneans have been studied. Variations in infection support the hypotheses that the main factor determining the infection of S. chrysophrii was temperature and that the parasite life cycle could be influenced by fish size and fish age. One hundred forty-nine of 280 S. aurata studied were infected. Seasonal differences in prevalence of infection were observed in all farms studied. A similar pattern was observed for parasite abundance with maximal infection levels occurring when water temperature were lower. A statistically significant dependence between infection and host size was also observed. The study of the surface topography of S. chrysophrii with scanning electron microscopy highlighted morphological adaptations not previously described. Parasites have developed diverse mechanisms of survival within the host that facilitate the establishment of infection. We mainly studied sensory structures and the anchoring systems of the parasite, i.e., filaments of eggs and haptor, enabling it to ensure the dispersal and survival of the species.