Atlantic bluefin tuna Thunnus thynnus L. is an economically significant species within world fisheries and catch-based aquaculture. Tuna fishing has been present in the Adriatic since the 15th century, and over time, the technique, tools and methods of its regulation have changed. Purse seine tuna fishing for further rearing is carried out every year in the determined period and is regulated by the Croatian Law on Marine Fisheries and bylaws of The International Commission for the Conservation of Atlantic Tunas (ICCAT). The presence of international and national observers is mandatory at tuna fishing and towing vessels. Based on the observation of tuna fishing in the Adriatic Sea in the period from May 28th to July 6th 2020 (40 days), through the role of a national observer, the technique of fishing juveniles and transporting them to farms was described. The protocols and regulations that need to be followed in order for tuna catches to comply with ICCAT laws and regulations are listed and described. The observation of the tuna fishing was carried out on towing vessel Pelagos III owned by Pelagos net farm Ltd. within the program of national observers of the Ministry of Agriculture of the Republic of Croatia, based on which the method of supervision and additional tasks for the purpose of collecting information on wild stocks of Atlantic bluefin tuna in the Adriatic is described. Also, based on observation during assisting the harvest in the period from February 14th to February 17th 2021, a further process of farming and harvesting from rearing cages, all the way to the market placement is briefly described following the example of the previously mentioned company.