The practice of tuna ranching has grown over the last few years, particularly in the Mediterranean, west coast of the US, Australia, Mexico and Japan. Some of the main farmed tuna species are Pacific bluefin, Atlantic bluefin, Southern bluefin and yellowfin.
For tuna ranching, tuna are first caught at sea when juvenile and are then transferred to a towing cage and then into a grow out/fattening farm.
Here, the fish are fed wild caught sardines, mackerel or pilchards in very large quantities until they are of a harvestable size.
So far, the progress in fattening operations has been limited with only small improvements in management and the reduction of mortalities. As ranching still relies on wild catches, for both production and feed, the line between aquaculture and fishing is also very blurred.
Tuna Aquaculture Developing
Following the achievement of closed-cycle Pacific bluefin tuna production and advances in hatchery technology, farming bluefin is becoming a reality in Japan.
The feasibility of closed-cycle production of other tuna species, such as bigeye tuna and blackfin tuna is also being examined.
Given the smaller size of blackfin tuna, it will be easier to transport and farm in smaller land-based facilities, said Dr Benetti.
Given its smaller size and high quality, it has potential as sashimi-grade tuna. However, it is unlikely to compete in the same global marketplace of its larger counterparts.
Attempts to expand the spawning cycle of southern bluefine tuna have so far been unsuccessful.
With these advances, the worldwide production of tuna is forecast to grow. However, more research still needs to be done into improving larval survival rates, as the survival rate of eggs collected from fish spawning in the cage are still below one per cent.
In terms of the future of tuna ranching, more must be done to understand and develop more sustainable feeds, as currently huge amounts of wild caught fish are used, Dr Benetti explained.