Fish diseases are always around

COURTESY TEXAS FISHERMEN have been seeing this a lot this year. Biologists say it is a common infection in fish call Columnaris.

Unless it is something like largemouth bass virus that results in a major die-off, the furthest thing from a fisherman’s mind is fish diseases. Worm versus swimbait versus frog is a much higher priority.

But just like the flu or a stomach virus moves through a human population from time to time, fish also suffer maladies occasionally.

That has been the case this year on a number of lakes in Texas as fishermen are finding bass missing scales on their sides. It appears as if the fish have been attacked, but in reality it is disease with an official name: columnaris.

It is one of those things that is not uncommon, especially in the spring, but also is not as common as it appears to be this year.

“It is a combination bacterial and fungal infection,” explained Richard Ott, Texas Parks and Wildlife Department Fisheries district biologist from Tyler. “We have been seeing it all over the place this spring. Usually it is related to something like spawning or temperature change that represses the fish’s immune system. Usually they recover.”

A common cause in the spring is rising water temperatures and can be heightened with the fish being in a weakened physical condition following spawning activity. It currently appears most prolific in bass, but that might be because they are so highly sought by fishermen on Texas lakes. The disease can impact most of the freshwater species found in the state and around the country. It can also result in the fish dying.

Columnaris is just one of many diseases that can flare up in a fish population. They constantly carry them around like humans.

“Most fish diseases are endemic in the population, meaning they are present all the time,” Ott explained. “They manifest as the disease when the fish are stressed. Fish usually recover as long as they keep feeding. If they are caught on rod and reel they are still feeding. The high number this spring has been unusual and is wide spread around East Texas lakes.”

Ott said another example of a common fish disease in Texas waters is lymphocystis.

“It is a viral infection that produces tumors on the exterior of the fish,” Ott said.  “Most often it looks like chewed chewing gum. Once again, this disease is endemic in the population and only shows up when the fish’s immune system is challenged by stress. We have been seeing a fair amount of it this spring also. Although I am not completely sure of the mechanism, both diseases were more common last spring and this spring when there was so much flood water.”

Diseases are spread in the fish community in different ways, including from fish to fish or from something existing in the water. They can be introduced into the water in several ways, including from birds or mammals, either existing on beaks or feet or through droppings.

Studies have shown that only a few fish parasites may be transmitted to humans who consume them. It is recommended, however, to either cook the meat thoroughly to 140 degrees or to freeze it at 0 degrees for up to 48 hours before consuming it. Ott added, when in doubt, simply don’t eat the meat.

Largemouth bass virus continues to be the most infamous of fish diseases to Texas fishermen. It rampaged through several Texas lakes starting with Sam Rayburn in 1998 and Lake Fork in 1999.

“We know it was transmitted by live fish and water transfer with the virus from lake to lake,” Ott said. “It appears to have run its course 15 to 20 years ago and has not been a problem since. It is likely that the fish that were susceptible died and those with natural immunity passed that immunity on to their offspring. We only ever saw one fish kill related to the disease on each lake; then it was over.”


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