The effect of water temperature on rhabdoviral dermatitis in the Japanese eel, Anguilla japonica Temminck and Schlegel

Rhabdoviral dermatitis has been occurring in the Japanese eel, Anguilla jap onica Temminck and Schlegel during the post-harvest stocking stage when the eels are kept in cages that are sprayed with well water (about 15 degrees C) while this disease never occurred in the warm water, farming ponds. This study evaluated the thermal effect on the outbreak of this disease using a pathogenic rhabdovirus that was isolated from the cutaneous lesions. In in vitro tests, this virus successfully replicated in the EPC cell line at te mperatures of 15 degrees C, 20 degrees C and 25 degrees C showing titer of 10(8.05) TCID50/ml after the 5th day post-inoculation at 25 degrees C while 10(8.55) TCID50/ml on the 9th day at 15 degrees C. In vivo, eels were inoc ulated by an intracutaneous injection at viral levels of 10(4.0), 10(6.4) a nd 10(8.4) TCID50/ml/fish and placed at three different water temperatures at 15 degrees C, 20 degrees C, and 25 degrees C. At 15 degrees C, inoculate d fish became moribund and displayed cutaneous lesions accompanied by necro sis of the dermal fibrocytes, hemorrhage and inflammatory cellular infiltra tion, and diffuse necrosis of the hematopoietic tissue, splenic pulps and h epatic parenchyma. At 20 degrees C, only one inoculated fish at 10(8.4) TCI D50/ml was moribund and displayed dermal lesions and splenic necrosis. At 2 5 degrees C, there were no moribund fish. (C) 1999 Elsevier Science B.V. Al l rights reserved.