Parvicapsula minibicornis infections in gill and kidney and the premature mortality of adult sockeye salmon (Oncorhynchus nerka) from Cultus Lake, British Columbia

Abstract

In recent years, large losses of migrating adult sockeye salmon ( Oncorhynchus nerka ) from the Fraser River, British Columbia, Canada, have resulted in reductions in catches and productivity. We investigated patterns of mortality and the occurrence of the myxosporean parasite Parvicapsula minibicornis in adult sockeye salmon from Cultus Lake, tributary to the Fraser River. Using data from a captive broodstock program, we found that early migrants to Cultus Lake had less severe P. minibicornis infections and were more likely to survive to maturity than those fish that arrived later after they had presumably held in the warmer Fraser River. We found P. minibicornis in kidneys and gills of spawners. In some fish, significant histopathology in the gills that included severe inflammation and hyperplasia of the gill lamellae was observed; the severity of the disease was correlated with the severity of P. minibicornis infections. Kidney and gill pathologies were more prevalent and more severe in fish that died before spawning compared with those that matured successfully. Gill disease associated with P. minibicornis infections had not been previously identified in Fraser River sockeye salmon, and its role in the loss of spawners needs further investigation.

Aerobic scope increases throughout an ecologically relevant temperature range in coho salmon

“…Indeed, salmonid exposure to temperatures above 13°C, which is ∼4-5°C above the modal temperature of the river during migration for these populations of coho salmon, just before or during spawning, can compromise gamete quality, lowering fertilization success and embryo survival (Richter and Kolmes, 2005). Also, pathogen growth, which is implicated in prespawn mortality of migrating adult Fraser River sockeye salmon (Miller et al, 2014), will occur slower at 10°C than at 15°C Bradford et al, 2010;Jeffries et al, 2012a). Indeed, many salmon diseases become virulent at water temperatures above 15.6-16.0°C (Richter and Kolmes, 2005) and fungal infections become especially prevalent at >18°C for sockeye salmon (Jeffries et al, 2012a).…”

Thermal exposure of adult Chinook salmon in the Willamette River basin

“…One thousand DD is an arbitrary total exposure threshold, but with testing, 1000 DD (or some similar threshold) can potentially serve as a proxy for a variety of physiological measures, from energetic costs (e.g., depletion of finite reserves) to premature maturation (e.g., over-ripening; Flett et al, 1996), and disease expression rates. There is considerable empirical support for a relationship between cumulative exposure and increased risk of lethal and sub-lethal effects from pathogens, bacterial infections, and fungal infections (e.g., Kocan et al, 2004;Bradford et al, 2010;Kent et al, 2013). In some Pacific salmon populations, total DDs as low as 500 have been predictive of disease expression and prespawn mortality (Wagner et al, 2005;Mathes et al, 2010).…”

Conservation physiology in practice: how physiological knowledge has improved our ability to sustainably manage Pacific salmon during up-river migration

“…Moreover, the longer a female salmon remains alive on spawning grounds, the higher the proportion of her total egg complement will be deposited [51]. Salmon that die on spawning grounds prior to spawning show physiological and histopathological profiles indicative of gill and kidney diseases playing a significant role in mortality, in particular those caused by P. minibicornis, Loma, Columnaris and Saprolegnia [52].…”