Most tuna farming operations rely on wild-captured fish for the stocking of net pens and utilize baitfish to feed tuna. The wild Pacific bluefin tuna population has declined due to excessive fishing pressure. San Diego, CA, once was known as the “Tuna Capital of the World”. Following the first tuna cannery startup, the city became a world leader in tuna-related commerce. By the 1960s, San Diego’s third-largest economic enterprise was tuna, superseded only by the U.S. Navy and aerospace, employing over 40,000 San Diegans but now this industry has all but disappeared from Southern California.
Today the sustainable production of farmed bluefin tuna is becoming a reality due to the remarkable advances in hatchery and feeding technologies in recent years. Here we share the recent success on tuna larviculture research and rearing of advance juveniles in RAS systems in San Diego. Fertile bluefin tuna eggs were sourced from collaborators in the Mediterranean Sea. Eggs arrived at the Ichthus Unlimited (IU) hatchery ~30 hours after the spawning (84% survival rate). Water parameters in the transport container were 19°C, 37 ppt and 170% saturation for water temperature, salinity, and dissolved oxygen, respectively. After acclimation to hatchery conditions eggs were stocked at a density of 18 eggs/L in 10, 500-L round tanks with a flow-through system. Flow rates were progressively increased to 0.5 L/min.
Yolk sac absorption was completed 2 days post hatch (dph). At this point the tuna larvae opened the mouth gape and exhibited predatory behavior. Enriched rotifers (Brachionus plicatilis, 10/mL) were the only source of exogenous feeding until 14 dph. At 14 dph, Artemia salina nauplii (0.5/mL) were provided in addition to rotifers. From 17 to 25 dph bluefin tuna larvae received and ad libitum provision of newly hatched red drum (Sciaenops ocellatus). Tuna larvae cannibalism was reduced by maintaining a suitable amount of prey at all times combined with frequent sorting-grading. Illumination regimes ranged from continual illumination to natural photoperiod starting 25 dph. Tuna larvae was weaned onto an artificial diet on 25 dph and metamorphosis was completed. At this point fish were transferred into a recirculation system. Throughout the rearing period, average environmental parameters were maintained at 25.6°C, 160% and 33.2 ppt for water temperature, dissolved oxygen saturation and salinity.
The survival rate of bluefin tuna juvenile >200 dph was relatively low at 3% rate and was due in part to an exceedingly low transport temperature which resulted in operculum malformations. Sourcing eggs near the hatchery should significantly increase survival rates. This research was funded in part by the Foundation for Food & Agriculture Research (American Aquaculture Program) and the Illinois Soybean Association.