Responding to Whirling Disease

by | Feb 14, 2017 | news | 0 comments

Responding to Whirling Disease in Alberta Waters
By Kate Wilson
Aquatic Invasive Species Specialist
Alberta Environment & Parks

Responding to Whirling Disease

Image Courtesy Alberta Environment and Parks

Whirling disease is becoming more widely known in North America as a serious fish health issue. It can affect salmonid populations including trout and whitefish and is caused by a microscopic parasite called Myxobolus cerebralis. The parasite also requires a segmented worm, Tubifex tubifex, a species native and common in Alberta waters. Myxobolus requires two hosts to complete its lifecycle – salmonid fish and the tubifex worm. The parasite is not transmissible to humans or wildlife.

The impacts of the disease can be highly variable, depending on species susceptibility and environmental factors, but can lead to spinal deformities, erratic swimming and death of affected fish. Not all susceptible species exhibit signs of whirling disease – for example, brown trout are known to be carriers/hosts of whirling disease, but have been found to be quite asymptomatic. Westslope cutthroat trout and some strains of rainbow trout, however, are highly susceptible. There is concern that a fish disease like this could really prove to be problematic for species at risk, especially in locations where there is already a fair amount of disturbance or habitat issues. Anglers will want to pay special attention to whirling disease positive waters, and ensure that they take the necessary steps to curb the spread of the disease to uninfected waters.

In August 2016, the first detection of whirling disease was reported in Canada, inside Banff National Park at a popular fly fishing spot, Johnson Lake. It is not known how the parasite was introduced, but research and literature suggest it is most commonly introduced primarily by the movement of infected fish, either by fish culture practices or anglers. It can then be spread downstream or with the movement of fish, but also by fishing and boating activities, any kind of in-water work, and even potentially waterfowl. The parasite is introduced to a waterbody in the form of microscopic spores found in the bottom of the river or earthen pond, in the sediment. The spores are then ingested by the tubifex worm, which is found in some waterbodies in Alberta. Fish most often contract the disease unknowingly, as once the parasite matures inside the infected worm, it produces tiny triactinomyxons (“TAMS”) that are carried in water currents and can infect a fish through the skin. Penetration of the fish by these TAM spores takes only a few seconds; within a few hours, the infectious sporoplasm is spreading via the nerves. This process takes days to weeks, eventually reaching the cartilage where most of the damage occurs. The organism has a sequential affinity for skin, nerves & finally cartilage of the fish. Once a tubifex is infected, it is infected for the life of the worm.

Responding to Whirling Disease

Image Courtesy Alberta Environment and Parks

Whirling disease mainly affects juvenile fish, such as fingerlings and fry, causing skeletal deformation and neurological damage. Fish exhibiting signs often “whirl” forward in an awkward, corkscrew-like manner, have difficulty feeding and are much more vulnerable to predators. The mortality rate can be high for affected fry/fingerlings with losses up to 90 percent of an infected population. Those that survive heavy infection may be deformed by the parasite’s destruction of cartilage and resulting abnormal bone formation (e.g. crooked tails). These survivors, as well as asymptomatically infected fish, are carrier fish that can then act as a reservoir for the parasite, which is released into water/sediment following the fish’s death.

The Government of Alberta took immediate action upon being notified of the detection in Banff National Park in August, working closely with the Canadian Food Inspection Agency (CFIA) and Parks Canada. The “Early Detection, Rapid Response” Plan developed for invasive Dreissenid mussels was utilized for the response, given the many similarities with an invasive mussel introduction (larvae are microscopic) and spread. An Incident Command System was set up to respond to the detection, as well as teams to address the myriad of aspects needed in a response, including policy development, risk assessments, mapping, communications and monitoring. Fisheries biologists province-wide were deployed to sample all “susceptible waters” in the province (e.g., waters that support trout and whitefish), which over the course of a few months equated to more than 200 sites in six watersheds.

Whirling disease cannot be detected directly in water or soil samples, so fish tissue must be sampled. Wild fish samples were collected last fall by Alberta Environment and Parks staff and stored in -80°C freezers; but we currently do not have the ability to analyze such large numbers internally, so this has created some delay in obtaining results. Samples are being processed by both CFIA labs and AEP labs; presently we’re working with the University of Alberta for molecular testing of Myxobolus cerebralis, a test which has more sensitivity than spore detection, thus is more appropriate for smaller fish. At this time, some salmonids in the Bow River watershed have yielded positive results for the Whirling disease agent. The CFIA posts positive results on their website when they are confirmed. Decontamination protocols are in development for all government staff conducting in-water work, and more information on the issue and what you can do can be found on the AEP website.
Currently, fish from several locations within Banff National Park, as well as many locations outside of the Park in the Bow River watershed (including some tributaries) have tested positive for Myxobolus cerebralis. In addition, fish from five private aquaculture facilities have also tested positive, all of which are currently under quarantine. This means that no fish or fish culture equipment is allowed to leave the positive facilities until infected fish are no longer present, the facilities are decontaminated and deemed to no longer be a risk by the CFIA and the Government of Alberta.

Responding to Whirling Disease-Clean Drain DryBe part of the solution! Fish diseases and aquatic invasive species are commonly spread by organic material (fish, plants), mud and standing water. It is imperative that anglers, boaters, aquatic ecologists, researchers and anyone coming into contact with water CLEAN all equipment, DRAIN any residual standing water and DRY watercraft, waders and equipment thoroughly before using again. These “boat and gear hygiene practices” are always a good idea, as this reduces the chances of spreading all kinds of aquatic invasive species. But these practices are especially important for those who are going from positive zones to susceptible waters. If possible, use hot water (90C) to wash your gear, and ensure water does not go down a storm drain or enter surface water. If you are using a boat, the drain plug must be pulled while in transport – it’s the law! Boat inspections are mandatory for all passing watercraft when inspection stations are open. Do your part to protect Alberta waters from aquatic invasive species and fish disease – CLEAN, DRAIN and DRY your watercraft and equipment before you leave the launch/lake every time. To report suspect fish or aquatic invasive species, please call 1-855-336-BOAT (2628).

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