Treatment of Monogenic Parasites in Imported HybridMono Sex Red Tilapia Fries (Oreochromis SPP)in the Sultanate of Oman

In February, 2008, 12000 fries of monosex red tilapia hybrid (Oreochromis SPP) of 0.2 g and 12000 fries of monosex Niletilapia (Oreochromis niloticus) of 0.5 g were imported from a hatchery in South East Asia and stocked in concrete raceways at an agriculturefarm in the Barka Region about 80 km from Muscat. Three days after stocking, mortality problems were observed. The preliminaryinspection revealed abnormal flashing movements of the fish with body scratching against the walls. Faint grayish white discoloration wasobserved externally on the skin and fins with focal hemorrhagic areas. Examination of skin and gill biopsies demonstrated the presence of alarge number of small sized monogenea parasitic worms attacking the tissue of these body regions. Histopathological observations revealedtissue reactions against the parasites and demonstrated a severe dermatitis of the skin, lamellar oedema and hyperplasia of the branchialtissue. A concomitant treatment regime using mebendazole, salt and formalin was practiced for three successive days and repeated threetimes every week together with parallel management procedures to enhance water quality during treatment. After treatment, a reduction ofmortality was noticed within three days and completely ceased after one week at which time biopsy examinations revealed the absence ofany parasitic agents. There were no deaths reported among the Nile tilapia, which were raised on the same farm.