Effect of water temperature on infections with the microsporidian Enterocytozoon salmonis in chinook salmon

Abstract

The effect of water temperature on the progress of infections associated with Enterocytozoon salmonis Chilmonczyk, Cox, Hedrick 1991 was examined in chinook salmon Oncorhynchus tshawytscha after intraperitoneal injections of mononuclear leukocytes infected with the microsporidlan 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 a t 9 and 12°C were shifted to 15°C and held for a n additional 8 wk. Among fish held a t constant water temperatures, severe infections occurred among exposed fish a t 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 slo\vly developed over time at 12'C and the cumulative mortality reached 73.7% between 13 and 20 wk. Although the development of the microspondian 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 g0C which were shifted to 15°C showed a cumulative mortality of 60 0% by 8 wk after transfer to the hlgher water temperature. Shifting the exposed fish from 12 to 15°C did not increase the mortality rate from that of fish kept constantly at 12OC. 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 Enterocytozoon salmonis Chilmonczyk, Cox, Hedrick 1991 is an intranuclear microsporidian associated with a severe anemic condition in salmonid fish, particularly, chinook salmon Oncorhynchus tshawytscha (Hedrick et al. 1990, Baxa-Antonio et al. 1992. Spontaneous infections with the microsporidian have also been reported in steelhead trout 0. mykiss (MacConnell et al. 1991) and among cultured populations of golden trout 0 . aquabonita and brook trout Salvelinus fontinalis (R. Hedrick unpubl. obs.). The progress of infection with the microsporidian has been described in chinook and kokanee salmon Oncorhynchus nerka (Hedrick et al. 1990(Hedrick et al. , 1991. Earlier studies documented the occurrence of similar infections in chinook salmon raised in sea water or fresh water (Elston et al. 1987, Morrison et al. 1990). We have demonstrated transmission of the parasite and the progress of infections in chinook salmon held in fresh and sea water (Antonio & Hedrick unpubl.).Enterocytozoon salmonis has been successfully propagated jn vitro using a newly developed culture medium (Wongtavatchai et al. 1994). Using parasites from in vltro cultures of infected leucocytes as an inoculum, the effect of infections on chinook salmon at 5 water temperatures was examined.Materials and methods. Juvenile chinook salmon (mean wt 20.0 g) were acclimated for 14 d at water temperatures of 9, 12, 15, 18 and 21°C in 132 1 a q u a~l a receiving f...

Impact of a water temperature shift on xenoma clearance and recovery time during a Loma salmonae (Microsporidia) infection in rainbow trout Oncorhynchus mykiss

“…The optimum temperature for the progression of infections occurs between 15 and 18°C, with the permissible range between 9 and 21°C (Antonio & Hedrick 1995). It was reported that at the low temperature of 9°C, mortality due to N. salmonis was delayed and the resultant infections were considered mild (Antonio & Hedrick 1995). A similar pattern was found with Loma salmonae in that the satellite fish at 11°C displayed a delayed rate of xenoma development of several weeks compared to fish held at 15 and 19°C.…”

“…Interestingly, fish infected with N. salmonis at 9°C and subsequently shifted to 15°C at Week 12 p.e. developed severe infections, with significantly higher levels of mortalities than fish that remained at 9°C throughout the course of the disease (Antonio & Hedrick 1995). Therefore, even at a relatively nonpermissive temperature of 9°C, N. salmonis infection occurs and can rapidly progress to severe disease with an upward shift in temperature to 15°C (Antonio & Hedrick 1995).…”

“…The optimum temperature for the progression of infections occurs between 15 and 18°C, with the permissible range between 9 and 21°C (Antonio & Hedrick 1995). It was reported that at the low temperature of 9°C, mortality due to N. salmonis was delayed and the resultant infections were considered mild (Antonio & Hedrick 1995).…”

Occurrence of the microsporidian parasite Nucleospora salmonis in four species of salmonids from the Massif Central of France

“…Hedrick et al (1990), Morrison et al (1990), andChilmonczyk et al (1991) characterised N. salmonis and the resulting symptoms of the disease. Infections in adult or juvenile salmon are usually characterised by severe anaemia and a leukaemic-like state (Antonio and Hedrick 1995). Nucleospora salmonis can affect several cell types but mostly and almost exclusively realises its life cycle in the nuclei of lymphopoietic-like cells, inducing in them an unusual lympho-proliferation.…”

Elevated Water Temperature Treatment of Ayu Infected with Glugea plecoglossi: Apparent Lack of Involvement of Antibody in the Effect of the Treatment.

“…Microsporidium takedai stopped development when infected fish were kept at 8.2-8.4•Ž (Awakura, 1974), and Glugea stephani required a temperature of above 15•Ž for its develop ment (Olson, 1981 (Olson, 1981;Antonio and Hedrick, 1995).…”