Normal and anomalous morphogenesis of splanchnocranium, vertebral column and fins in reared larvae and post larvae of atlantic bluefin tuna Thunnus thynnus.

The reproduction control of bluefin tuna in captivity has been recently achieved in the Mediterranean 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 skeleton ontogenesis. 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) (EU project SELFDOTT and other Italian projects). 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). The reared BFT used for studying the skeletogenesis had an age varying between 0 and 41 DPH: up to 30 DPH BFT one half of samples were selectively in toto stained with Alizarin red and the other half with Alcian blue. The remnants were double stained. As many as 22 wild BFT (SL range: 114-244 mm) were also included in the analysis for skeletal anomalies. The results evidenced both similarity and dissimilarity with the pattern described by Potthoff (1975) in T. atlanticus and by Potthoff et al. (1986) in the family of Scombridae, genus Thunnus included. The observed skeletogenic sequence was the following: splanchnocranium (at first: Meckel cartilage, maxillary and dentary), neurocranium (palatine) and pectoral fins → vertebral column → caudal complex, pelvic girdle and fin, first dorsal fin → second dorsal fin, anal fin and finlets. Same length (SL) or age individuals were found at different skeletogenic stages. Skeletogenic data are used to infer information on swimming capability during larval and post-larval phases useful for the setting up of proper rearing conditions. Anomalous morphogenesis investigation evidenced, inter alia, the presence of 100% of samples affected by at least one anomaly (all the samples showed an uninflated swimbladder), with severe skeletal anomalies (detectable at gross examination) representing the 31% of the total observed anomalies. The average anomalies charge (number of total anomalies/number of malformed individuals) and the severe anomalies charge augmented with age/size of BFT, as well as the affected body regions. Asymmetry in the number of paired fin rays was found in the 83% of samples. Fractures of palatine bone have been largely found in 10-37 mm SL BFT.