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Disease could affect hatchery operations

Bruce Ajari
Gone Fishin'

The Truckee River Watershed Council hosted a meeting on Wednesday, Dec. 6, on the subject of Bacterial Kidney Disease caused by the bacterium Renibacterium salmoninarum (RS), a disease that affects both hatchery and wild salmonids (trout and salmon).

It was an informative session with panel members from the California Department of Fish and Game and the United States Fish and Wildlife Service.

Doctor William Cox, a fish pathologist from the California Department of Fish and Game and a disease expert, gave a very good Powerpoint presentation on the disease that is listed as serious by the California Department of Fish and Game.

The disease is of great concern to hatchery operations, but the disease itself is very difficult to detect because it rarely shows in fish less than 6 months of age. Cox indicated that the pathogen that causes Bacterial Kidney Disease is already present in the Truckee River drainage. He felt that there was no reason for concern for wild fish at the moment because stocked fish must meet the Department’s stocking criteria.

The California Department of Fish and Game’s policy prohibits planting of diseased fish, and its regulations prohibit the importation of diseased (or infected) fish or eggs from broodstock testing positive for serious fish pathogens.

However, during his presentation, Cox did indicate in a response to a question regarding the impact of regulated flow regimes that if the environment degrades (becomes stressful), or fish become concentrated, RS infections could progress to a disease state. And concentrations of fish would facilitate horizontal transmission in the population.

The reason that the disease is serious is that it is a slowly progressing disease that affects trout by shutting down the kidneys. I asked Cox after the meeting if trout could develop an immunity to the disease over time. He indicated that the there was no cure and likened the disease to Tuberculosis. It kills.

The disease can be transmitted vertically and horizontally. Vertical transmission is from parent to child, a hereditary link. Horizontal transmission is the passage of the disease through water, by nearness to a carrier animal, or by the ingestion of an infected fish, snail, copepod, or other animal.

Because of the typically soft water in the Truckee River, the Pathogen could only survive about seven days in normal conditions, thus making the concern for transmission of the disease in wild fish populations lower in risk, Cox said.

The disease occurs when environmental conditions are poor or stressful and/or host is susceptible. As Cox indicated, there is no “successful” treatment for the disease.

In the mid 1990’s, around 1996 or 1997, anglers were very concerned with an outbreak of some disease that turned out to be a Bacterial Gill Disease (not BKD) in Martis Lake. Very large Eagle Lake strain rainbows were dying off in very large numbers. The fish that we saw during this period would beach themselves on the shore or in the vegetation before dying. Many of the fish had issues with their eyes, which appeared in bright red or orange. There also was some appearance of white fungus on their bodies.

Bacterial Kidney diseased fish apparently have similar issues with their eyes showing a pop-eyed effect or their bellies being distended. You may also see blisters on their bodies or other damage to their eyes.

As anglers, if we catch fish that show symptoms of disease, Cox recommends that we place the fish in a plastic bag, put it on ice and then call the Department of Fish and Game. The Fish Health Laboratory can be reached at (916) 358-2822.

It is very important to provide this feedback to them because diseased wild fish are rarely seen. Predators and natural decomposition quickly remove them from view.

Slow diseases such as this may weaken the fish and they can die from other causes such as predation. A weakened fish is also less capable of responding to environmental changes and is less capable of feeding.

While BKD was the topic of the forum, there are a number of other diseases that are known to be in our region, including whirling disease. As anglers out on the water, we can provide some valuable feedback should an outbreak such as the one in Martis Lake occur.

Bruce Ajari is a Truckee resident and regular fishing columnist for the Sierra Sun and other area newspapers.


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