In a world first, South Australian based aquaculture company Clean Seas Tuna Ltd has successfully spawned and reared southern bluefin tuna in a state-of-the-art on land aquaculture hatchery.
The hatachery’s SBT brood stock, some weighing as much as 160kg, were artificially manipulated to spawn in the closed environment of their on land tank. By manipulating environmental parameters such as water temperature and photoperiod, the tuna are fooled into believing they have arrived at their spawning grounds off the coast of Java.
After a couple of years of on land conditioning, these adult brood stock reacted to the parameters as expected, supplying fertilised eggs, which were transferred to the adjoining hatchery. As rearing SBT larvae in captivity is still in the research and development stage, a host of tank designs and parameters were trialled in an attempt to work out the best rearing conditions for these pelagic larvae.
Southern bluefin tuna larvae (left) and egg.
The newly hatched SBT were highly predatory and cannibalistic and were fed a host of live food during their early larval development. At the time of writing the fish are approximately 70 days of age and around 15cm in length. It has been a major breakthrough to have success with this important commercial and recreational species.
Southern bluefin tuna larvae.
The current tuna industry of Port Lincoln revolves around the capture and subsequent fattening of wild caught fish. These fish are per sained from the wild, kept alive in a floating sea cage for three to five months, before being harvested for the Japanese market.
The Port Lincoln wild caught SBT fishery has a capped quota; the demand of increased seafood consumption is currently met through environmentally sustainable aquaculture, as the wild caught tuna fishery cannot increase beyond its current level.
In the long term, replacing wild caught southern bluefin tuna with hatchery reared fish to take pressure off wild fish stocks is the ultimate goal for Clean Seas Tuna Ltd.
