FIRST PRODUCTION OF ATLANTIC BLUEFIN TUNA LARVAE AND JUVENILES IN RECIRCULATING AQUACULTURE SYSTEMS IN NORTH AMERICA  

Tunas are considered the most valuable fishery in the world. Globally, Atlantic bluefin tuna (ABFT; Thunnus thynnus) is the species with the greatest market value, but this species has also experienced one of the steepest declines of all current fisheries. The ever-growing demand and declining supply has led to strong interest in developing ABFT aquaculture. However, these efforts have focused mostly on the unsustainable capture and fattening of wild populations. For several years, academic and industry groups in Japan, Europe and Australia have intensely conducted research on broodstock management, larval rearing and grow-out of several bluefin tuna species including Pacific, Southern and Atlantic bluefins. Rearing feasibility studies in environmentally sustainable, recirculating, land-based facilities have not, however, been reported yet for any bluefin tuna.

During the summer of 2015, ninety-five ABFT broodstock (200-250 Kg each) held in two floating net-pens in the Adriatic Sea off the coast of Croatia were induced to spawn using GnRHa-loaded slow-release implants, which were administered intramuscularly by free divers. Massive spawning events occurred thereafter, starting in early July and continuing through late August. On 6 occasions, fertilized eggs were collected in the early morning, cleaned, packaged and shipped to the USA (Maryland) where they arrived 36-40 hours post-spawn, usually as newly hatched larvae. These larvae enabled initial experiments and advances in hatchery and nursery technologies for ABFT in recirculating systems maintained with synthetic seawater. The effect of multiple combinations of biotic and abiotic parameters and several diets on larval ontogenetic development and survival, as well as on metamorphosis and survival to the fingerling stage, were tested. We aimed at understanding and resolving the typical constraints experienced in tuna aquaculture, such as minimizing surface tension-related mortalities during the first 2 days post-hatch, promoting inflation of the swim-bladder, reducing sinking mortalities, monitoring the occurrence of post-flexion and accurate timing of the initiation of piscivorous feeding, minimizing cannibalism, improving the weaning process, and preventing wall collisions. These studies led to the production of hundreds of post-larvae and a few juveniles that survived to 60 days post-hatch or beyond. Additional research on stage-specific culture and system design is ongoing.