aquaculture of the bluefin tuna. taxonomy genus thunnus species: maccoyii, orientalis, thynnus
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Aquaculture of the Bluefin Tuna
Taxonomy
Genus ThunnusSpecies: Maccoyii, Orientalis, Thynnus
Economic importance, market price, market locations, country
The Atlantic bluefin is a highly sought-after delicacy for sushi in Asia
A single fish has sold for around 1.8 million dollars
The largest driver of demand for bluefin tuna is the market in Japan.
Life cycle and larval stagesScientists in Japan achieved
completion of the life cycle under controlled conditions after 32 years.
Not achieved on commercial-scale, capture based aquaculture has developed significantly.
The larvae are ~3mm when they hatch and grow at a rate of 1mm per day after that.
Female bluefins reach sexual maturity at about 5 years old.
Reproduction in captivitySpawning occurs from April to June in the Gulf of
Mexico and from May/June to August in the Mediterranean.
Sexual maturity of Atlantic bluefin tuna is reached at the age of 5-8 years, while Eastern Atlantic maturity is reached at 4-5 years.
Bluefin tunas may release from 5 to 30 million eggsSpawning occurs in open water close to the surface
and in areas where survival expectations are highest.
Production Methods
Bluefin tuna farming based on stocking of wild-caught individuals Purse seine is the most effective capture system Wild tunas are caught at different life-cycle stages Fish finders and sonar are used to detect Bluefin tuna schools They are kept alive and transferred to towing cages usually by sewing the nets
together, difficult and inefficient Tugboats used to transfer tuna in the towing cages to farm site. Low
transportation speed critical, cause for long trips In Mediterranean, the companies start stocking their tuna cages in May/June Mediterranean tuna farms use circular ring type open-sea floating net cages.
Size of cages vary from 30-90m in diameter, with net depths ranging from 15-30m
Farming cages designed to contain smaller tuna specimens for long periods of time. Fattening season is linked to market demand/opportunity
Quotas put in place by ICCAT (International Commission for the Conservation of the Atlantic Tuna) to limit the number of tuna harvested
Feeds and Feeding
Bluefin tuna are fed with a mixed diet composed of a variety of small pelagic species
Proportion and volume of feed varies among the farms of different countries
The Mediterranean countries engaged in the tuna farming obtain bait fish from locally fished stocks
Fed 1-3 times a day with a mixture of defrosted bait fishWhen the tuna are not fed at own pleasure, daily input varies from 2-10%
of the estimated tuna biomassDifficult to record initial weight or length measurements without losing the
tuna in the handling process, little information about food intake so overfeeding is a common practice.
Feed conversion ratios are 15-20:1 for large specimens and 10-15:1 for smaller fish
They maintain a high body temperature and their constant movement implies a high energy demand, resulting in 5% of total energy input is used for body growth
Water chemistry and environmental requirements in culture
Spawning has only been recorded where the waters are 25-30C
Advantages and disadvantages of the speciesDisadvantages: Advantages:Long life before they can be
harvestedA closed life-cycle has not
yet been achieved for practical use
There is not yet an effective feeding practice
High demandHigh market priceThey are becoming extinct,
so aquaculture is beneficial Mediterranean area benefits
by making huge financial investments that have allowed the modernization of equipment