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Western Fisheries Science News, March 2016 | Issue 4.3

Understanding the Effects of Temperature on Diseases in Fish

Pacific herring demonstrating visible signs of VHS
Pacific herring demonstrating visible signs of VHS, including hemorrhaging around the eyes, mouth, and fins. Photo by USGS WFRC.

Diseases in fish are increasingly recognized as an important component of the health of aquatic and terrestrial ecosystems, affecting both population dynamics and ecosystem function. Natural populations of fish are threatened by emerging and reemerging diseases due to many factors such as introduction of novel pathogens, ecosystem alterations, contaminants accumulation and a changing environment.

Researchers from the U.S. Geological Survey’s WFRC and colleagues have been studying the effects of water temperature on important fish pathogens. The health of both freshwater and marine fish species may be directly or indirectly affected by variations in water temperature. As ectothermic (regulation of body temperature depends on external sources) animals, the fish immune system that protects against pathogens is highly dependent on environmental temperature. Pathogens also have an optimal temperature range for growth and shifts in temperature can influence pathogen virulence.  While there has been much attention on opportunistic diseases caused by warming waters, a range of temperatures can influence patterns of disease.

Renibacterium salmoninarum is the agent that causes bacterial kidney disease (BKD), a significant disease of Pacific salmon. In a study by Maureen Purcell and colleagues Purcell, M. K., et al. 2015, R. salmoninarum-infected Chinook salmon were held at three different temperatures.  Fish held in cool water (8°C) had significantly higher R. salmoninarum-specific mortality, kidney bacterial loads and bacterial shedding rates compared to fish held at warmer temperatures (12 or 15°C). The research demonstrated that water temperature influences disease progression possibly by altering the replication of the pathogen and altering the fish immune system. This research supports the hypothesis that R. salmoninarum may present a lower risk to Chinook salmon under a climate warming scenario relative to other opportunistic bacterial pathogens. These results may be useful in future efforts to model transmission and disease dynamics.

Viral hemorrhagic septicemia (VHS) is a highly contagious disease in fresh water and marine fishes throughout the northern hemisphere. Paul Hershberger at the Marrowstone Marine Field Station (MMFS) and colleagues have been investigating conditions, including temperature, that preface periodic VHS outbreaks in wild populations throughout the NE Pacific. A study by Hershberger, P. K., et al. 2013 demonstrated that Pacific herring maintained at 8, 11, and 15°C and infected with the virus that causes VHS, had cumulative mortalities of 78%, 40%, and 13%, respectively. Pacific herring were susceptible to VHS at all temperatures examined; however, disease severity decreased with increasing temperature.  These results indicate that temperature is likely a leading environmental factor contributing to patterns of VHS outbreaks in wild fishes in the NE Pacific. Thus, cooler water temperatures should be included in a list of primary VHS risk factors for populations of wild Pacific herring and other susceptible sympatric species.

Ichthyophonus is an ecological and economically important parasite of marine and anadromous fishes worldwide. The parasite is very common in Pacific herring, an important forage fish species, throughout the NE Pacific. Researchers at the MMFS examined the effects of temperature on Ichthyophonus infection in juvenile Pacific herring maintained under simulated overwinter fasting conditions Gregg, J. L., et al. 2011. The researchers found that parasite infectivity was inversely related to temperature, with the prevalence of infection decreasing (76%, 54%, and 24%) as the temperature increased (9, 12, 15°C; respectively). Further, temperature influenced disease outcome if the manipulation was applied early in infection (within 1 day of infection), as the mortality due to Ichthyophonus was suppressed at both the low (~6°C) and high temperatures (12°C) but not at the intermediate temperature (~9°C). These results suggest a complex interplay between temperature optima for the parasite and the fish host immune system. These experiments provide new insights into factors influencing patterns of Ichthyophonus disease in wild herring populations.

These studies demonstrate that water temperature does impact aquatic disease dynamics but the direction and magnitude of the temperature effect is also dependent on the biology of the host and pathogen. 

Newsletter Author - Debra Becker



USGS Recently Awarded NIFA Grant to Develop Immunological Tools for Fish:  The WFRC will lead a research team titled CIRNAS - Collaborative Immunological Research Network for Aquacultured Species through a proposal funded by the USDA National Institute of Food and Agriculture. A major factor restricting the advancement of basic and applied research for fish health is the lack of immunological reagents. These reagents are required for evaluating shifts in immunity during infection and vaccination against pathogens that limit the full potential of aquaculture. The CIRNAS is composed of federal (USGS) and university scientists (University of New Mexico and the University of Pennsylvania) with the object of developing immunological tools (monoclonal antibodies and assays) for fish. In particular, four fish species: Atlantic salmon, rainbow trout, channel catfish and Nile tilapia will be studied. The reagents will be provided to the research community for addressing fish health of farmed and wild fish.

USGS Scientists Participated in Expanding Your Horizons STEM Conference: WFRC scientists Maureen Purcell and Carla Conway participated in a Science, Technology, Engineering, and Math (STEM) conference “Expanding Your Horizons”, intended for girls grade 9-12 at Bellevue College, WA. Purcell and Conway presented a hands-on workshop with NOAA Fisheries colleague Krista Nichols titled “Fish Get Sick Too!” that focused on the use of microbiology and molecular biology to diagnose a mysterious salmon disease.

USGS at North American Wildlife and Natural Resources Conference:  WFRC scientists spoke at the North American Wildlife and Natural Resources conference in Pittsburgh, Pennsylvania. WFRC Center Director Jill Rolland and supervisory research microbiologist James Winton gave a talk titled “Infectious Salmon Anemia, Infectious Hematopoietic Necrosis and Bacterial Kidney Disease as Case Studies for Disease Management in Farmed and Hatchery-reared Salmonids” in a special session focused on science-based management strategies for fish and wildlife diseases.


Scientists from Laos Receive Training at the WFRC Columbia River Research Laboratory (CRRL):  As part of a DOI International Technical Assistance Program (ITAP) project begun in 2015, visiting fishery scientists from the Laos Living Aquatic Resources Research Center and the National University of Laos recently received two weeks of training from scientists at the WFRC CRRL in Washington and Oregon. The use of up to 11 new dams on the Mekong River, one of the most productive rivers in the world, is a key part of Lao economic development plans, but poses significant ecological risks. As part of the ITAP project, the two foreign scientists will spend three months in the USA to learn about a variety of scientific methods from DOI. During their time at the CRRL in February 2016 they focused on structural and operational aspects of dams, advanced fish tagging and monitoring methods used to study fish movements and dam passage, and database management. Their training included tours of Bonneville Dam, a 60-ft tall run-of-river hydroelectric dam on the Columbia River, and Cougar Dam, a 500-ft tall flood-risk-management dam in western Oregon. Beeman traveled to Laos in 2015 as part of the same ITAP project to assess the current capacities of the government fishery research program and help craft a capacity building agenda to meet future needs.


Thornton, E.M., J.J. Duda, and T.P. Quinn. 2016. Influence of species, size and relative abundance on the outcomes of competitive interactions between brook trout and juvenile coho salmon. Ethol. Ecol. Evol. 29(2): 157-169.

Jager, H.I., M.J. Parsley, J.J. Cech Jr., R.L. McLaughlin, P.S. Forsythe, R.F. Elliott, and B.M. Pracheil. 2016. Reconnecting fragmented sturgeon populations in North American rivers. Fisheries 41(3): 140-148.

Hershberger, P.K., J.L. Gregg, L.M. Hart, S. Moffitt, R. Brenner, K. Stick, E. Coonradt, E.O. Otis, J.J. Vollenweider, K.A. Garver, J. Lovy, and T.R. Meyers. 2016. The parasite Ichthyophonus sp. in Pacific herring from the coastal NE Pacific. J. Fish Dis. 39(4): 395-410.

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