SEAFDEC Contribution No. 215.

Aeromonas hydrophila was consistently associated with necrotic ulcers and lesions in mudfish/snakehead (Ophiocephalus striatus), Thai catfish (Clarias batrachus), crucian carp (Carassius carassius) and goby (Glossogobius giurus) in Laguna de Bay, Philippines, during the months of December 1985 through February 1986. The bacterium was isolated from body lesions and ulcers of all fish examined and rarely from the kidney and liver of carp and catfish. The disease was characterized by hemorrhages, lesions and open necrotic ulcers on the body of the fish, particularly the head (just behind the eyes), the mandible and the maxilla, and the caudal peduncle regions. Erosion of the head bone tissues and the tails was observed in very severe cases. The presence of A. hydrophila is believed to be secondary to some predisposing factors existing in Laguna de Bay.