A survey was conducted on the incidence of diseases, by superficial appearance, in common fish species of Portonovo coast. Approximately 46,484 marine and 22,150 estuarine fishes were examined. Marine fishes alone were observed with fin rot and neoplasm while estuarine fishes were free from such abnormalities. Fin rot was recorded among seventeen species of marine fish and tumour in cat fish. Fin necrosis accompanied with haemorrhage, ulceration and loss of scales was consistent external sign of the disease. Species of cat fish, grunter, queen fish and pikes were mostly affected by fin rot at high level and the maximum peak was recorded in April. Cat fishes alone had tumour. More than 80% of the tumour bearing specimen had fin necrosis.