Broodstock is the most important stage in aquaculture. One of the obstacles in broodstock maintenance is disease. Some pathogens can cause death quickly and in large quantities. Cryptocarion irritans is a parasite that often infects Seabass (Lates calcarifer ) broodstock, especially those kept in tanks. Every year, this parasite infection always occurs and caused mass mortality of Seabass broodstocks in the Mariculture Centre Batam. This confirmed by laboratory data, which shows that apart from the broodstock, the high pathogenicity of this parasite also causes mortality in other fish seeds such as pompano with a mortality rate 80 - 100%. The last case in May 2023 was 15 Seabass broodstocks weighing 2-5 kg kept in one tank, positive for Cryptocarion irritans infection. A total of 12 fishes died with clinical signs of a smooth body, no wounds or nodules on the body surface, pale gills with excessive mucus production. The results of microscopic observations showed that the parasite was round in shape and surrounded by cilia with an average diameter of 231.8 µm, actively moving with high intensity and was identified as Cryptocarion irritans in the trophon phase. A more severe outbreak occurred in September 2022, as many as 15 broodstocks in one tank wasdeath. The treatment was done for infected broodstocks were carried out by dipped in formalin at dose 150 – 200 ppm, moving the broodstocks to a new tank. But deaths still occured. The next control step was to move the broodstocks to floating net cages in the sea and significantly reduced mortality. Apart from that, preventive efforts are also carried out by regularly monitoring the condition of the fish by swabbing mucus and observing in the laboratory.