Description of the unusual digestive tract ofPlatax orbicularisand the potential impact ofTenacibaculum maritimuminfection

Abstract

BackgroundEphippidae fish are characterized by a discoid shape with a very small visceral cavity. Among themPlatax orbicularishas a high economic potential due to its flesh quality and flesh to carcass ratio. Nonetheless, the development of its aquaculture is limited by high mortality rates, especially due toTenacibaculum maritimuminfection, occurring one to three weeks after the transfer of fishes from bio-secure land-based aquaculture system to the lagoon cages for growth. Among the lines of defense against this microbial infection, the gastrointestinal tract (GIT) is less studied. The knowledge about the morphofunctional anatomy of this organ inP. orbicularisis still scarce. Therefore, the aims of this study are to characterize the GIT in non-infectedP. orbicularisjuveniles to then investigate the impact ofT. maritimumon this multifunctional organ.MethodsIn the first place, the morpho-anatomy of the GIT in non-infected individuals was characterized using various histological techniques. Then, infected individuals, experimentally challenged byT. maritimumwere analysed and compared to the previously established GIT reference.ResultsThe overlapped shape of the GIT ofP. orbicularisis probably due to its constrained compaction in a narrow visceral cavity. Firstly, the GIT was divided into 10 sections, from the esophagus to the rectum. For each section, the structure of the walls was characterized, with a focus on mucus secretions and the presence of the Na+/K+ATPase pump. An identification key allowing the characterization of the GIT sections usingin totohistology is given. Secondly, individuals challenged withT. maritimumexhibited differences in mucus type and proportion and, modifications in the mucosal and muscle layers. These changes could induce an imbalance in the trade-off between the GIT functions which may be in favour of protection and immunity to the disadvantage of nutrition capacities.