Sustainable farming of bluefin tuna
An industry based on the capture of tuna has developed in the Mediterranean Sea in recent years. The process involves taking wild fish during their migration and fattening them in cages for periods ranging between two months and two years. An alternative to the fishing and capture of BFT is to farm them in a sustainable way, which can help relieve the pressure on wild stocks, but cannot completely replace fishing altogether. The EU-funded Selfdott project was established to help develop BFT aquaculture by obtaining fertilised eggs and studying the embryonic and larval development for the production of juvenile fish. A better understanding of the life cycle of the BFT will help improve management of wild stocks. Wild juvenile and mature fish were reared at a site in southern Spain and a site in Malta. Adult fish were induced to spawn using an implant loaded with gonadotropin releasing hormone analogue (GnRHA). The Spanish fish spawned two days after treatment and the fertilised eggs were collected. The Maltese fish did not spawn, possibly as a result of lower water temperature at the site. The next challenge was to ensure the survival of the larvae by investigating optimal light levels, hydrodynamics, surface cleaning, microalgae, feeding sequence and nutritional quality. Scientists applied techniques originally developed for bonito, a type of mackerel which belongs to the same family as BFT. Juvenile tuna grow extremely rapidly; as a result they have very high nutritional demands. Researchers conducted feeding trials with young BFT. A diet of raw fish was compared to a diet of artificial food and the results showed that tuna require a diet that is high protein and low in fat. The project's findings will aid the development of pelleted feed for growing juvenile fish, thereby reducing the need to import raw fish for the fattening industry and the emerging tuna farming sector. Sustainable farming of BFT will be able to help conserve wild stocks by meeting some of the global demand for the fish. Consumers will also benefit because farmed fish are of a standard quality and can be easily traced, thereby allowing people to know exactly what they are buying.
