How To

How to Recognize 9 Common Game Fish Diseases

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Just like land animals, fish also suffer from all manner of maladies and parasites. Disease is one of the prime factors in fish mortality and can range from viral or bacterial ailments to fungal infections. But how do you recognize these diseases, and should you keep an affected fish? Is it safe to eat? What should you do to prevent the spread of the disease?

Below are descriptions of nine common diseases and parasites found across game fish in the United States, as well as information on what they are caused by, whether or not the fish is still edible, and how you should dispose of uneaten portions. The information is primarily sourced from Maine’s Department of Inland Fisheries and Wildlife, Minnesota’s Department of Natural Resources, the US Fish and Wildlife Service, and other agencies.

This fish looks "cooked" even before you put it on the skillet.

This fish looks “cooked” even before you put it on the skillet.

Heterosporis

If you have ever noticed a fish with flesh that resembled cooked meat without being cooked, you may have encountered heterosporis. This parasite affects yellow perch, walleye, northern pike, rock bass, and other fish. The parasite is actually spread by spores that come from from infected fish or carcasses. It does not cause mortality by itself, but will infect the fish’s muscles and produce spores at an alarming rate. The spores can eventually replace muscle matter altogether. There have been recorded instances of fish being found with 90 percent of their muscle tissue replaced by the spores.

Sometimes fish diseases can seem like they come straight out of a sci-fi horror movie.

Is it safe to eat?

There is no evidence that the parasite affects humans, yet many anglers will not eat fish affected by heterosporis. Experts advise cooking affected meat thoroughly before consumption.

How should I dispose of uneaten portions?

Parts of affected fish can be disposed of in the trash or buried, but should never be discarded into a body of water.

How can anglers prevent its spread?

Never release unused minnows into a body of water. If you catch fish with these parasites, please report it to wildlife officials.

A close up of VHS on an affected fish.

A close up of VHS on an affected fish.

Viral hemorrhagic septicemia (VHS)

VHS affects a variety of fish, including black crappie, bluegill, common carp, muskie, white bass, yellow perch, channel catfish, northern pike, rock bass, rainbow trout, Chinook salmon, and a number of other species. VHS is an infectious viral disease that can cause widespread fish kills, and spreads when infected fish move from one body of water to another. Symptoms often involve widespread hemorrhages, especially from the eye, skin, and fins, although internal bleeding is also common.

Is it safe to eat?

Yes, the virus has no impact whatsoever on humans.

How should I dispose of uneaten portions?

Parts of affected fish can be disposed of in the trash, but should never be discarded into a body of water.

How can anglers prevent its spread?

Do not move live fish between bodies of water and drain water from your boat, livewell, and other areas before leaving the access area. It is suggested to let your boat and gear dry for 12 hours before entering another area.

LEARN MORE ABOUT WILDLIFE DISEASES: How to recognize 5 common, lethal deer diseases

Despite not being fatal, a fish affected by lymphosarcoma can be quite unsightly.

Despite not being fatal, a fish affected by lymphosarcoma can be quite unsightly.

Lymphosarcoma

If you have ever seen these cauliflower-like growths on a muskie or northern pike, you have seen lymphosarcoma. This viral disease is transmitted between fish by physical contact, often during spawning or in crowded waters. Severe infections are fatal but many fish live to be caught by anglers, who are then puzzled by the strange disease. It is most commonly seen during the fall and winter and tumors can range from grayish white to blood red. Even though the virus has been known of for at least 80 years, scientists still know very little about the disease.

Is it safe to eat?

Uncertain. Experts are not sure what effects, if any, the consumption of affected fish will have on humans. It is currently suggested that anglers avoid eating fish with this disease.

How should I dispose of uneaten portions?

Parts of affected fish can be disposed of in the trash or buried, but should never be discarded into a body of water.

How can anglers prevent its spread?

There are no known methods of limiting this disease’s spread.

Have you seen these grape-like clusters before?

Have you seen these grape-like clusters on a fish before?

Dermal sarcoma

This viral infection only affects walleye and is spread through physical contact. Dermal sarcomas are not usually associated with fish mortality, yet the condition can cause skin lesions that penetrate into the fish’s muscles. If a fish has this disease, you will usually find evidence of it on its skin in the form of grape-like clusters of growths.

Is it safe to eat?

Yes, although experts advise cooking the fish thoroughly before consumption.

How should I dispose of uneaten portions?

Parts of affected fish can be discarded normally with household waste, but should never be discarded into a body of water.

How can anglers prevent its spread?

There are no parctical methods of limiting this disease’s spread.

Lymphocystis is quite similar to dermal sarcoma, can be more severe for the fish.

Lymphocystis is quite similar to dermal sarcomas, and can be severely to a fish’s health.

Lymphocystis

A viral infection that effects a vast number of freshwater and saltwater species, lymphocystis is not usually fatal but severe infections can cause death due to organ damage. The most noticeable symptom of the disease is the fungal growths, or “warts” that can grow on the skin of fish. Infections typically are highest in the late winter and early spring.

Is it safe to eat?

Yes, although experts advise cooking the fish thoroughly before consumption.

How should I dispose of uneaten portions?

Parts of affected fish can be disposed of in the trash or buried, but should never be discarded into a body of water.

How can anglers prevent its spread?

There are no practical methods of limiting this disease’s spread.

Tapeworm in an infected bass.

Tapeworm in an infected bass.

Bass tapeworm

This disgusting parasite is found in both largemouth and smallmouth bass and are particularly gruesome in their method of transmission. The tapeworm larva develops in crustaceans and other fish, but grows into an adult once introduced to a bass. Adult tapeworms will then swell, burst, and spew a number of eggs which will be released with the fish’s feces.

The presence of the parasite causes damage to the fish’s liver, spleen, and reproductive organs, sometimes causing the internal organs to appear as a single mass. On the outside, it would appear that the fish has a potbelly.

Is it safe to eat?

If you don’t mind the tapeworms, affected bass can still be consumed without danger. Make sure you cook your fillets thoroughly.

How should I dispose of uneaten portions?

Parts of affected fish can be disposed of in the trash or buried, but should never be discarded into a body of water.

How can anglers prevent its spread?

Be careful when transporting live bass from one lake to another, as well as releasing live baitfish.

Symptoms of this disease include yellowish mineral deposits.

Symptoms of this disease include yellowish mineral deposits.

Myofibrogranuloma

This viral disease is believed to only affect walleye and can cause areas of opaque, dry flesh that resemble a freezer burn. Not much is known about the disease although scientists suspect that it is not infectious, and may be caused by genetics or environmental stressors.

Is it safe to eat?

Uncertain. Experts are not sure what effects, if any, the consumption of affected fish will have on humans. It is currently suggested that anglers avoid eating fish with this disease.

How should I dispose of uneaten portions?

Parts of affected fish can be disposed of in the trash or buried, but should never be discarded into a body of water.

How can anglers prevent its spread?

There are no known methods of limiting this disease’s spread.

SVC can cause anemia, darkened skin, and pale gills in addition to other symptoms. Image courtesy Dr. Andrew Goodwin/MN DNR.

SVC can cause anemia, darkened skin, and pale gills in addition to other symptoms. Image courtesy Dr. Andrew Goodwin/MN DNR.

Spring viremia of carp (SVC)

SVC is a serious viral disease that affects carp species and can cause widespread fish kills. The virus weakens a fish’s immune system and can cause symptoms such as lethargy, dark skin, pop-eye, swelling, and severe hemorrhaging. In addition to carp, SVC has also been observed to affect fish like northern pike, rainbow trout, bluegill, and largemouth bass.

Is it safe to eat?

Yes, the virus has no impact whatsoever on humans.

How should I dispose of uneaten portions?

Parts of affected fish can be disposed of in the trash, but should never be discarded into a body of water.

How can anglers prevent its spread?

Do not move live fish between bodies of water and drain water from your boat, livewell, and other areas before leaving the access area. It is suggested to let your boat and gear dry for 12 hours before entering another area.

Neascus is fairly noticeable due to dark spots in the fish's flesh.

Neascus is fairly noticeable due to dark spots in the fish’s flesh.

Neascus (black spot disease)

Many fish species are affected by this parasite, which comes in the form of black spots on the fish’s flesh. The parasite is very common in many parts of the country and is hard to limit. Also known as “black grub,” the neascus parasite is spread by fish-eating birds that deposit their eggs into water. From there, the parasite enters a snail and incubates until it finds a fish. When that happens, the parasite burrows into the fish and encloses itself in cysts.

Is it safe to eat?

Yes, although experts advise cooking the fish thoroughly before consumption.

How should I dispose of uneaten portions?

Parts of affected fish can be disposed of in the trash, but should never be discarded into a body of water.

How can anglers prevent its spread?

There are no known methods of limiting this disease’s spread.

All images courtesy Minnesota Department of Natural Resources and US Fish and Wildlife Service, thumbnail image from imgur

Any views or opinions expressed in this article are those of the author and do not reflect those of OutdoorHub. Comments on this article reflect the sole opinions of their writers.
  • nae

    this is good to know. I searched it because we found black spots in a minnow in the lake and i was wondering wat it was. Thanks!!