Several diseases have been encountered in cultured brown-spotted grouper and silvery black porgy in the mariculture facilities of the Kuwait Institute for Scientific Research. More than 50% of juvenile brown-spotted grouper cultured in concrete tanks died during an initial outbreak of the protozoan parasite Cryptocaryon irritans. Formalin treatment (35–50 mg/L, 5 h/d, twice a week) was used to control and prevent the disease. Formalin-treated fish experienced several reinfestations by this parasite, but no further deaths occurred. Brown-spotted grouper also suffered from severe eye lesions, including exophthalmia and opaqueness of the cornea. Only 35% of these fish cultured in fiberglass tanks did not have idiopathic lesions. Silvery black porgy cultured in floating cages in the open sea did not show any lesions from July to November 1985 apart from eroded fins, which increased in frequency with increasing stocking densities. However, a disease occurred during the winter of 1986, when the water temperature averaged 14.8°C, and 65% mortality resulted. Vibrio anguillarum, V. ordain, V. carchariae, V. damsela, and three other Vibrio spp. were isolated from diseased silvery black porgy. Deaths associated with broken isthmuses occurred among silvery black porgy cultured in floating cages in August 1987. There was no further incidence of this condition after the addition of vitamin C (500 mg/kg) of feed to the diet.