WHIRLING DISEASE EDUCATION PROJECT
WHAT IS WHIRLING DISEASE?
Whirling disease affects salmonid fish (e.g., trout, salmon, whitefish) that get infected by a tiny parasite called Myxobolus cerebralis. The parasite relies on two essential intermediate hosts: salmonid fish (like trout), and the “boogie worm” Tubifex tubifex. Infected young fish often develop skeletal deformities resulting in a ‘kinked’ spine that makes the fish swim in a circular “whirling” pattern. While whirling disease does not affect humans, it impacts fish survival rates and can lead to significant population declines.
WHIRLING DISEASE RISK TO THE ELK RIVER WATERSHED
Originally from Europe, M. cerebralis was first detected in North America in 1958, and in 2016 it was first reported in Canada in Banff National Park’s Johnson Lake. Over the following five years, infected fish were found in many Albertan watersheds, including the Crowsnest River. Whirling Disease was detected in British Columbia’s Emerald Lake in 2023, resulting in the closure of the Yoho and Kootenay National Parks for one year. The Crowsnest River is a mere 15 minute drive from the Elk River Watershed in BC; a careless transfer of wet boating, fishing, or wading equipment could easily cause disease transmission. Additionally, in 2020 the Elk River Alliance detected DNA presence of the Tubifex tubifex worm in the Elk River Watershed, meaning both essential M. cerebralis hosts are present (see section below). Over the next two years the Elk River Alliance will continue monitoring tributary streams for Tubifex worm presence to assess the risk of whirling disease establishment.
A ONEWAY STREET
Once established, getting rid of Whirling Disease is impossible as there are no known cures or treatments. The Westslope cutthroat trout and Mountain Whitefish, two target fish that support a thriving fishing tourism industry in the Elk Valley, have a high risk of being infected and suffering population declines. All downstream watersheds, such as the Kootenay River and Columbia River, will have a higher risk of transmission. It is up to all users of the Elk River Watershed to ensure transmission is slowed down.
CAUSES OF SPREAD & PREVENTION
Although whirling disease can spread naturally through fish movement or bird faeces, a major cause of spread is human activity. Because there are no known treatments for whirling disease, the main preventative method is not exposing fish to M. cerebralis in the first place. A single fish can contain thousands of spores, so it is essential that live fish or fish parts do not get transferred between streams. As recreational river users move from one stream to another, there is a considerable risk of picking up M. cerebralis spores and transferring them on boats or fishing equipment. To prevent “hitchhiker” invasions, the best-practice method recommended by the Province of British Columbia is to Clean, Drain, and Dry all your equipment. Studies have shown that drying even the resilient spore stage significantly reduces the infectious ability of M. cerebralis.
To learn more about Government of BC clean drain dry please visit https://www2.gov.bc.ca/gov/content/invasive-mussels/what-can-you-do
CLEAN
Thoroughly inspect boat (hull, drive units, trim plates, transducers), trailer and components (rollers, bunk boards, axles, etc.), equipment (i.e., water pumps, hatchery equipment, siphons, nets, ropes, traps, etc.) and remove any mud, dirt, plants or aquatic species. Some aquatic invasive species are very small such as New Zealand mud snails and can be found in small amounts of mud or dirt. Pay attention to hidden, hard to reach areas, gaps, crevices, holes and other inconspicuous places (i.e., around the motor housing, trim tabs, and water intake screens, or pump fittings).
DRAIN
Whenever possible, areas that hold water should be drained so there is no standing water. Eliminate water from any conceivable item before you leave the visiting area. This includes live wells, bilges, cargo areas, pipes, water pumps, etc.
DRY
Dry all areas of the vessel that may have gotten wet for 24 hours. Drying boats, gear and equipment will help to minimize risk of contamination.
OTHER INVASIVE SPECIES PREVENTED BY CLEAN DRAIN DRY
ZEBRA AND QUAGGA MUSSELS
Not yet detected in BC
Native to Eurasia, these mussels spread fast by growing on all substrates and reproducing rapidly. Both species can alter food webs by filtering out nutrients and can cause millions of dollars of damage to hydroelectric dams, fisheries, and recreation.
EURASIAN MILFOIL
Present in BC
The Invasive Milfoil outcompetes and replaces native aquatic vegetation with its dense stands. It also interferes with freshwater lakes, streams, ponds, and irrigation ditches. It may also limit the amount of recreational activity due to its dense formation.
WHIRLING DISEASE BIOLOGY
M. cerebralis is a relative of corals, anemones, and jellyfish (Phylum: Cnidaria). It has two life stages: the spore stage and the triactinomyxon (TAM) stage. These stages switch between infecting the Tubifex tubifex worm and salmonid fish. While TAMs are fairly fragile, spores can survive adverse environmental conditions such as high temperatures, low pH, digestive enzymes, and freezing.
LIFECYCLE STAGES
- Tiny Myxobolus cerebralis spores in the water column get eaten by the Tubifex tubifex worm
- The spores open up in the worm gut and develop into a Triactinomyxon (TAM). The TAM stage exits the worm with worm poop
- TAMs float in the water column and attach to the fish skin
- TAMs inject the fish with cells that develop into the spore stage within the fish cartilage
- The spores get released when the fish dies, and float in the water column until they get eaten by the Tubifex worm again. The cycle repeats.
WHAT CAUSES SYMPTOMS?
After the TAM attaches to the salmonid fish skin:
A. The TAM injects cells that will grow into spores through mucous cells in the fish skin.
B. The cells travel along nerve cells to the fish cartilage.
C. As the cells develop into spores they feed on fish cartilage, weakening it.
D. This causes inflammation, which deforms the fish spine and puts pressure on pigment nerves, resulting in a black tail.
WHIRLING DISEASE SIGNS & SYMPTOMS
BLACK TAIL
Inflammation of the tissues surrounding cartilage puts pressure on the nervous cells responsible for pigmentation of fish skin, inducing high pigmentation and a black tail.
SKELETAL DEFORMATION
A kinked tail and truncated misshapen skull can be indicators of whirling disease infection. As M. cerebralis develops within salmonid fish, it feeds on cartilaginous tissue. This not only deforms and weakens the cartilage but induces an inflammatory response from the fish immune system. The inflammation causes constriction of the spinal cord, which results in a bent tail shape. It is important to note that other disorders can also cause deformities, and they do not necessarily mean whirling disease infection.
WHIRLING SWIMMING PATTERN
The namesake of “whirling” disease comes from the erratic swimming behaviour fish develop after infection. Deformities in the spine and brainstem of the fish prevent it from controlling the swimming direction. This behaviour not only exhausts the fish but makes it more visible to predators and less capable of escape.
DEATH
Fish can die directly from whirling disease degrading their body, or by incidental consequences of whirling disease. Because of the weakened and deformed skeletal system, infected fish have a decreased ability to find food and escape predators. This greatly decreases their chance of survival.
WIDESCALE EFFECTS
Drastic population declines of trout species have been attributed to whirling disease in many streams. In some rivers in Colorado, trout declines exceeded 90% of the population in less than two decades since disease detection. Since not all trout species are equally susceptible to infection, the disproportionate impact on one trout species could result in a change of the species present in rivers. Of fish found in the Elk River, the partially resistant Bull Trout could be less impacted than the susceptible Westslope Cutthroat Trout and Mountain Whitefish (see Sarker et al., 2015).
Additionally, cumulative effects from many factors acting in combination with whirling disease could increase the chance of population declines. In the Elk Valley, various land uses and recreation activities already impact fish habitat, so the addition of whirling disease could act as “the straw that breaks the trout’s back”. Fish hatcheries are also concerned as infection can require fish quarantine and spread necessitates discarding entire hatchery stocks.
DETERMINANTS OF DISEASE SEVERITY
Although M. cerebralis presence or even infection does not mean fish will show symptomatic signs, in some cases infection results in 90% mortality of young fish. Infection severity is determined by: fish age, fish species, temperature, and the extent of M. cerebralis TAM exposure.
AGE
Age is perhaps the most important factor when determining salmonid disease risk. While fish eggs are not susceptible to infection, immediately after hatching fish are at very high risk of serious infection. In one experiment, a group of 2-day old alevin that were exposed to 100 TAMs contained over 40,000 spores two months later and suffered a 91% mortality rate. Even 7-week-old juvenile Rainbow trout (one of the most susceptible species) exposed to TAMs showed clinical signs of infection and increased mortality rate. One of the reasons young fish are thought to be more prone to infection is that a greater proportion of their skeleton is made of cartilage, rather than bone. Older fish, despite not showing symptoms, may still act as a disease carriers.
SPECIES
So far, only salmonid fish are known to be susceptible to whirling disease infection, and not all salmonids are equally at risk. Some salmonid fish have not yet been recorded to develop symptoms and are thus considered more resistant to whirling disease. Conversely, rainbow trout/steelhead salmon (Oncorhynchus mykiss) are highly susceptible and readily show clinical signs of infection even when exposed to a low parasite load. What determines each species’ susceptibility to whirling disease is so far not known, but genetic differences in an ability to mount an effective immune response seems to be a likely factor. This effect can even be seen within different strains of the same species. German rainbow trout, for instance, are considerably more resistant to infection than US rainbow trout because they have had over a century of exposure to whirling disease.
TEMPERATURE
Studies show that temperature is a key determinant of M. cerebralis development. Within Tubifex tubifex, temperatures of 10-15C result in the highest production of TAMs, and salmon infected at 10-12C develop the most severe symptoms. Unfortunately, these are similar temperatures to those the Elk River Alliance measures in key salmonid spawning habitat during early summer, when salmon eggs hatch into alevins and are most susceptible to severe infection.
PARASITE LOAD
As with many diseases, more infective agents result in a greater risk of symptomatic infection. While as few as 10 TAMs can cause symptomatic disease in some species, high TAM numbers can cause infection of juvenile fish even in less susceptible species. Because of this, a slowed introduction of whirling disease could be effective in preventing extreme fish population decline.
REPORT A FISH
IF YOU FIND A FISH YOU SUSPECT OF WHIRLING DISEASE INFECTION
Report it to the Elk River Alliance. Include a photo, your location, and the fish species (if you can).
INFO@ELKRIVERALLIANCE.CA
ABOUT THE PROJECT
This 3-year project aims to educate local and out-of-province river users about whirling disease biology, risk of spread, and prevention methods. Additionally, we will engage volunteers in tests of tributary streams for DNA evidence of one of the key hosts of whirling disease Tubifex tubifex. This will serve as a stewardship opportunity for locals, and inform ERA about the potential risk of spread of Myxobolus cerebralis into the Elk River Watershed.
2022
- Research & Development
- Content and digital asset design
- Video development
- Pamphlet distribution
- Social media promotion
- First year of Tubifex tubifex monitoring
2023
- Restocking pamphlets
- Social Media Promotion
- Second year of Tubifex tubifex monitoring
2024
- Restocking pamphlets
- Social Media Promotion
- Third year of Tubifex tubifex monitoring
- Reporting
PROJECT FUNDERS
PROJECT PARTNERS
Whirling disease photos courtesy of Dr. Sascha Hallett, Oregon State University
