Reproduction and physiology
Controlled reproduction is a crucial step on the road to domesticating a wild species. We need to understand the environmental cues and parameters that initiate the maturation process and control it. We need to know the size and age at first spawning in both sexes. We have to study the hormonal regulation on gonadal development, maturation of gametes, spawning and fecundity, and finally develop suitable methods to control the reproduction of the Atlantic bluefin tuna (Thunnus thynnus). The availability of captive brood stock will allow us to increase the knowledge about the input of reproduction cues to recruitment determinism in the wild, hence allowing a better management of the resource.
In order to develop an aquaculture farming technology for the Atlantic bluefin tuna, it is of utmost importance to improve our knowledge on the reproductive biology of the species, as well in the wild as in captivity. This was achieved by establishing protocols for an effective sampling of fish and by selecting appropriate methods to assess their hormonal and gametogenetic status. For this task to be done successfully, it was crucial to predispose collaboration with both fisheries scientists expert in the migratory routes of Atlantic bluefin tuna and the fishing fleets from various Mediterranean countries. The Atlantic bluefin tuna being a migratory species, the reproductive status at fishing time is the consequence of preceding uncontrolled events; the possibility to monitor a captive brood stock will provide valuable and original information on the influence of external factors on the reproduction process in big pelagic migratory fish.
A major objective of the project was to assess the capability of BFT brood stock to mature and spawn in captivity. This required the use of appropriate facilities for the confinement of a brood stock that allow fish to swim at their desired speed without the danger of coming into contact with the enclosure walls. A large stock of Atlantic bluefin tuna was held in the cage for a long period (3 years). During the natural spawning period (May-August), a thorough observation of the fish in the brood stock was made to detect presumable courtship or reproductive behaviour.
The main aim of reproduction in aquaculture is to provide fry in any circumstance whatever the way to obtain them, that is, we have first to assess the feasibility to obtain viable eggs from Atlantic bluefin tuna breeders. Thus, irrespective of natural spawning and egg fertilization in cage-reared Atlantic bluefin tuna, it was necessary to develop suitable methodologies to obtain viable high quality gametes from wild and/or cage-reared fish during the spawning time. The application of hormonal induction techniques for Atlantic bluefin tuna maturation and spawning will be useful, especially if the fish do not spawn naturally in captivity.
The implementation of the above tasks required the suitable and safe management of the livestock, so we needed to develop handling methods for routine operations in Atlantic bluefin tuna aquaculture. This included testing the effectiveness of different anaesthetics and anaesthesia procedures, the use of adequate transport systems for live fish, the development of egg collection methods and the utilisation of non-invasive methodologies for sexing and monitoring maturation.