Parasites and hepatic lesions among pink salmon, Oncorhynchus gorbuscha (Walbaum), during early seawater residence.

Juvenile pink salmon, Oncorhynchus gorbuscha (Walbaum), in the Broughton Archipelago region of western Canada were surveyed over 2 years for sea lice (Lepeophtheirus salmonis and Caligus clemensi), gross and microscopic lesions and evidence of infections with viruses and bacteria. The 1071 fish examined had an approximate ocean residence time no longer than 3 months. A high prevalence of degenerative liver lesions, renal myxosporean parasites and a low prevalence of skin lesions and sea lice were observed. No indications of viral or bacterial diseases were detected in either year. The monthly prevalence of sea lice in 2007 (18-51%) was higher than in 2008 (1-26%), and the infestation density exceeded the lethal threshold in only two fish. Degenerative hepatic lesions and renal myxosporean parasites occurred in approximately 40% of the pink salmon examined in June of both years, and the peak monthly prevalence of hepatocellular hydropic degeneration was greater in 2007 (32%, in May) than in 2008 (12%, in June). Logistic regression analysis found skin lesions and hepatocellular hydropic degeneration significantly associated with sea lice. Most parasites and lesions occurred during both years, but the prevalence was often higher in 2007. Fish weight was 35% less in June 2007 than in June 2008, but condition factor was not different. Further research is required to monitor inter-annual variations and aetiology of the liver lesions and to assess their potential role on pink salmon survival.

Infectious haematopoietic necrosis epidemic (2001 to 2003) in farmed Atlantic salmon Salmo salar in British Columbia.

I investigated a recent infectious haematopoietic necrosis disease (IHN) epidemic in farmed Atlantic salmon Salmo salar in British Columbia (BC), Canada. All companies with infected farms (n = 36) participated in the study. Over 12 million Atlantic salmon on infected farms died or were culled during the epidemic with cumulative mortality on the farms averaging 58%. The first reported case of IHN occurred in August 2001 and the last outbreak in June 2003. Outbreaks on the farms lasted between 20 and 22 wk. Genetic sequencing by other researchers, revealed that 2 different IHN isolates contributed to this epidemic, one linked to all cases in 4 areas, the other associated with all cases in a fifth area. Spatial and temporal patterns of the farm outbreaks were examined to determine possible methods of spread between the farms. Evidence presented herein appears to show that farming practices themselves contributed significantly to the spread between farms both within and between areas. Natural waterborne transmission may have played a role in the spread of the virus between farms located in close proximity to each other. The data collected from this epidemic are compared with reports which examined the first reported epidemic in Atlantic salmon in BC (1992 to 1996). Evidence is presented for the hypothesis that wild fish species may have been the source of introduction of the virus into the farmed Atlantic salmon population.

A field evaluation of an indirect immunofluorescent antibody test developed to diagnose plasmacytoid leukemia in chinook salmon (Oncorhynchus tshawytscha).

An immunofluorescent antibody test (IFAT) developed for the diagnosis for plasmacytoid leukemia was evaluated against histology under field conditions. Previously published results from a laboratory evaluation indicated that the IFAT had a much higher sensitivity than did histology. One hundred seventy-seven moribund chinook salmon from 3 farms located in British Columbia were sampled. Sensitivity, specificity and their respective quality indices were estimated for the IFAT relative to histology. The IFAT was shown to be unreliable, particularly with respect to sensitivity. Cohen's kappa was also calculated and revealed that the agreement between the 2 tests was no better than random. In contrast to previously published results the IFAT did not perform better than histology in the presence of bacterial kidney disease. The results emphasize the importance of evaluating tests in the field conditions in which they are to be used. The possible reasons for the shortcomings of the IFAT are discussed.

Production of monoclonal antibodies specific for antigens derived from tissue of chinook salmon (Oncorhynchus tshawytscha) affected with plasmacytoid leukemia.

Two distinct monoclonal antibodies (MAB) were prepared for testing with kidney, spleen, and retrobulbar tissue imprints made from chinook salmon (Oncorhynchus tshawytscha) affected with plasmacytoid leukemia. (PL). Hybridomas were prepared from mice immunized with whole and lysed cells purified from renal or retrobulbar PL-positive tissues, which had been obtained from naturally and experimentally infected fish from British Columbia, Canada. The MAB reacted with at least 4 morphologically different cell types; fluorescence was associated with the plasma membrane and cytoplasm. The MAB also reacted with kidney imprints made from chinook salmon affected with a PL-like lymphoproliferative disease in California, indicating that these 2 diseases might be caused by a similar agent. The MAB did not react with any of the kidney or spleen imprints made from wild chinook salmon collected from a river in Ontario, Canada.