Contribution à l'étude des relations entre des poissons de la famille des Carapidae et leurs hôtes invertébrés

Among possible associations in sea, different Carapidae fish are able to live within various invertebrates such as holothuroids, starfishes and bivalves. In this study, a multidisciplinary approach is realised to understand the biology of the Carapidae fish and to highlight the various factors which make these associations possible. Two research axis were carried out. The first axis attempts to establish Carapidae evolution. These approach was realised by comparisons 1) of the anatomy (muscles, skeleton, ligaments, dentition and otoliths), 2) of the functional morphology (feeding and sonic apparatus), 3) of the larvae development and 4) of the way of life of fish from the genera Pyramodon, Snyderidia, Echiodon, Onuxodon, Carapus and Encheliophis. The Carapidae may be divided in five ecomorphological groups which are placed on an ecological gradient leading to parasitism. The pelagic ancestor group gave rise to a benthic taxon. The latter could be at the origin of two distinct taxa of commensal fish. Within the Carapus clade, a group would have evolved to the parasitic life. The second axis of the study provided elements elucidating various aspects of the Carapini (Carapus and Encheliophis) behaviour. The morphofunctional study of the bucco-pharyngeal apparatus, the stable isotopes of carbon (13C) and nitrogen (15N), the stomach content determinations and the study of otolith increments allow to define clearly the commensal behaviour of Carapus and the parasitic behaviour of Encheliophis. The study of the larval development (axial skeleton and otoliths) reveals that the association between the fish and the host is obligatory, as the fish needs its host to initiate its metamorphosis. The hosts could be used as a bridal room. The capacities to emit sounds were also highlighted and the structures (skeletal, muscular and of the swim bladder) responsible were identified and described. The fish use the sound production at least to communicate inside the host but experimental manipulations also show that the fish are unable to determine if a host is already occupied or not.