engleski

Tuna farming - a Croatian practice

From sudden success and expansion of Adriatic tuna farms from late 90-ties onwards, tuna fattening in Croatia developed in a long term rearing cycle up to 2 years, being in this sense unique in the Mediterranean. The primary cause of such a prolongated encagement period lays in the fact that each year smaller tuna are caught, thus needing a longer period to gain their marketable size. Even this practice evokes serious concerns regarding its long-term sustainability from the biological and ecological point of view, it made possible planned and thorough study of this fish in the rearing system, helping to enlighten some missing points in tuna physiology. Today there are 5 tuna farms in Croatia, dispersed between islands of central Adriatic Sea, with the overall year production of 4500 t. For the past year, the ICCAT quota was 1069 t. Purse seiners mainly in the water of the Island of Jabuka catch the fish, while few farms catch also older fish from the Mediterranean and harvest it after 6-10 months in cages. Small fish under 10 kg are broth and transferred in cages of 50-60 m in diameter, 19, 25 or 30 m in depth, with the eye width of 55-85 mm. Tuna diet composition depends strongly on the seasonal availability of Adriatic purse seine catch. During the warmer months tuna are fed with fresh pilchard, anchovy, sprat, mackerel and Spanish mackerel, in combination or alone with imported frozen sardine and herrings. The food quantity strongly depends on the sea temperature and baitfish fat content. Preliminary histological observations suggest first signs of maturity in fish over 20 kg, while below this weight only adipose and connective tissue is found. Findings of spawned males in August suggest a possible spawning in the cages, even though the process seems to be temperature and individual-dependent. The mortalities induced by pathogens are mainly related to the exposition of a long term feeding stress (misbalanced, wrongly stored or food of poor quality), coupled and complicated afterwards with the secondary bacterial diseases.

bluefin tuna; adriatic sea; rearing

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