J. Appl. Ichthyol. zyxwvutsr 10 (1994), 204-208 zyxwvutsrqp Q 1994 Blackwell Wissenschafts-Verlag, Berlin zyxwvu ISSN 0175-8659 zyxwvutsrqpon Received: July 23, 1993 Accepted: March 14, 1994 zyxw Association of Aeromonas hydrophilcl with epizootic ulcerative syndrome (EUS) of freshwater fish in Sri Lanka By A. PATHIRATNE', G. S. WIDANAPATHIRANA~ and W. H. S . CHANDRAKAIWHI' 'Department of Zoology; 'Department of Minobiology, University of Kelaniya, Kelaniya, Sri Lunka Summary Aeromonas hydrophila was the predominant bacteria isolated from the haemorrhagic lesions and necrotic ulcers in the seven species of fish, Etroplus suratensis, Ophkephalus zyxwv striatus, Puntius sarana, Rasbora danicornius, Trichogaster pectoralis, Tor khudree lon ispinnis and Wallago attu affected by e izootic ulcerative syndrome(EUS), during the 1990 and 1991 iisease outbreaks in Sri Lanka. Severely akected fish were truly septicemic, as A. hydrophila was recovered from their internal organs. A. hydrophila isolated from diseased fish and injected intramuscularly into healthy E. suratensis and 0. striatus induced dermonecrotic lesions resemblin EUS. The results suggests that A. h drophila is consistently associated with EUS in Sri Lanka anfmay play an important role in the patlogenesis of the disease. Introduction Since 1980, epizootic ulcerative syndrome (EUS) has been observed in brackish and fresh- water fishes in many areas of Southeast Asia (ROBERTS et al. 1992). The disease was first noted in Sri Lanka in late 1987, around the lower reaches of the Kalani River where heavy mortalities were caused among brackish and freshwater fish in the South-Western Zone (COSTA and WIJEYARATNE 1989). Since then, outbreaks of EUS have occurred annually following prolonged periods of dry weather, particularly from November to March. The disease has now spread to fish in a large number of waterbodies in both the Wet and Dry Zones of Sri Lanka, affecting over 20 species of food fish. Experimental work has indicated that the disease could be transmitted to Ophicephalus striatus and 0. punctatus either by direct contact with water from infected environments or by feeding with infected fish (BALASURIYA et d. 1990). The causative agent of EUS is not known with certainty. Initially, a rhabdovirus was isolated from lesions of affected fish and thought to be the causative agent of EUS (FRERICHS et al. 1986). Several species of bacteria and an invasive fungus have also been associated with EUS lesions (BOONYARATPALIN 1986; SUBASINGHE et al. 1990). Aeromonas hydrophilu was reported to be the predominant pathogen found in the lesions of EUS-affected fish in the Philippines (LIo-PO et al. 1992). This paper presents the results of our bacterial investigations on EUS - affected fish in Sri Lanka during 1990 and 1991. Materials and methods Fish: Fish showing varying degrees of clinical signs of EUS were collected from zyx six water- bodies in the districts of Chilaw, Gampaha, Kalutara, Kegalle and Tangalle during 1990 and 1991. The fish were brought to the laboratory and maintained at 28"-30°C in glass aquaria filled with water collected from the natural habitats. Fish were not provided with food. Isolation and identification of bacteria: Bacteriological samples were collected aseptically from skin lesions, kidney, liver and spleen of 22 diseased fish belonging to seven species: U. S. Copyright Clearance Center Code Statement: 0175-86591941 1002-0204 $1 zyxw 0.50lO