Sequenhal development of PKX, the causative agent of prohferahve h d n e y dlsease, is descnbed in rainbow trout Salmo ga~rdnen hchardson by light and electron mlcroscopy Fish were exposed to water contaming the infechous stage of PKX and the parasite was detected 3 wk later Parasites were prominent the following week and they mulhplied by endogeny, binary fission and possibly plasmotomy in the blood and h d n e y intershhum Intershbal nephnbs that is typically assoclated \nth PKD was fust observed 5 wk after exposure and was most prominent between 8 to 11 wk At 7 wk parasites were found in the lumens of the tubules, many were daughter cells released from PKX Myxosporean sporoblasts formed within these daughter cells (enveloping cells) The sporoblasts consisted of 6 cells and some organized into spores w~t h 2 spherical polar capsules Although the spores persisted for several months after the interstitial PKX and assoclated inflammation had subsided they dld not complete their development They remained within the enveloping cell and apparently dld not form complete valves Because only incomplete spores were observed salmonids may be abnormal hosts and the preclse taxonomic status of PKX was not determined Epizoohological and sequential development data support the hypothesis that the interstitial form of PKX and the intraluminal myxosporeans belong to the same organism

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...

A virus (SGV) was isolated from sand goby Oxyeleotris marrnoratus with ulcer disease reared in freshwater cages in Thailand. The virus was typical of members of the aquatic birnaviruses but it possessed phenotypic, serological and biochemical properties that distinguished it from previously described viruses of the Bimaviridae. Serologically, the virus is distinct from the described strains of infectious pancreatic necrosis virus (IPNV) and possesses the capability of replicating in several cell lines from warm water fishes at 30 'C. The use of rapid double-stranded RNA analyses and the immunoprecipltation of radio-labeled virion polypeptides demonstrated the unique biochemical nature of SGV and established the value of these techniques for strain identification of birnaviruses.

No abstract