ABSTRACT: The effect of water temperature on the progress of infections associated with Enterocytozoon salmonis Chil-monczyk, Cox, Hedrick 1991 was examined in chinook salmon Oncorhynchus tshawytscha after intraperitoneal injections of mononuclear leukocytes infected with the micro-sporidian parasite. Experimentally infected and control fish were held at water temperatures of 9, 12, 15, 18 and 21*C for 12 wk and then one half of the exposed and control groups of fish at 9 and 12*C were shifted to 15*C and held for an additional 8 wk. Among fish held at constant water temperatures, severe infections occurred among exposed fish at 15 and 18*C resulting in 90.0% cumulative mortality in both groups. Disease and significant mortality was also observed at 21*C (47.5%). The parasite and signs of the disease slowly developed over time at 12*C and the cumulative mortality reached 73.7% between 13 and 20 wk. Although the development of the microsporidian was not arrested at a water temperature of 9*C, infections in chinook salmon were not severe and cumulative mortalities were low (10.0%). However, parallel groups of exposed chinook salmon at 9*C which were shifted to 15*C showed a cumulative mortality of 60.0% by 8 wk after transfer to the higher water temperature. Shifting the exposed fish from 12 to 15*C did not increase the mortality rate from that of fish kept constantly at 12*C. The control fish (not exposed to E. salmonis) in all temperature groups did not show signs of the disease nor mortality throughout the study.

KEY WORDS: Enterocytozoon salmonis . Water temperature . Chinook salmon . Microsporea

Published in DAO Vol. 22, No. 3 (1995) on July 13
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 1995