Digestive apparatus and sense organs ontogenesis in atlantic bluefin tuna Thunnus thynnus.

The reproduction control of bluefin tuna in captivity has been recently achieved and the setting up of proper larval rearing is actually the main challenge to be faced for the conversion of “capture-based” Atlantic bluefin tuna industry in the Mediterranean Sea into a real self-sustained aquaculture. This study was aimed at improving the knowledge on the early life history of this species, paying a special attention to the digestive apparatus and sense organs ontogenesis in order to optimize larval feeding in rearing conditions. Fertilized eggs of bluefin tuna (BFT) were obtained from spawning induction of broodstock in net cages at the Mare Nostro hatchery, near the coast of Vibo Marina (Vv) (South Tyrrhenian Sea, Italy). These fertilized eggs were secondly sent to two commercial hatcheries, the Panittica Pugliese (Torre Canne di Fasano (Br), Italy) and the Civita Ittica S.r.l. (Civitavecchia, Italy). As many as 131 reared and wild BFT were used for studying ontogenetic development and 2 wild adult tunas for describing the adult morphology of all the organs involved in feeding behaviour. Observations were carried out by mean of conventional histological and SEM procedures. The atlas of morphological features of the entire digestive apparatus (taste buds included) of wild adult tuna is the first original result. Secondarily, the study on ontogenetic pattern of alimentary tract and of outer and inner sense organs evidenced that i) BFT early stages at the same length (SL) or age show different ontogenic stages; ii) the differentiation of all organs involved in feeding is achieved very early, inner taste buds included, that is before the notochord flexion. Further, postlarvae showed inner taste buds in all the anterior digestive tract (buccal rim, oro-pharyngeal cavity and anterior oesophagous), conversely to adult (only in pharynx), thus bestowing to the early stages a higher responsiveness than adults to the organoleptic property of food items.