Unfortunately we have quite a bit of experience dealing with major fish kills here in Texas to the point that we have a group of people in TPWD that work on nothing but fish kills. To name a few examples that people are probably familiar with, we had a large bass kill at Sam Rayburn in 1998 due to largemouth bass virus. Toledo Bend experiences striped bass kills often in the summer due to temperature stress. In West Texas there are major die offs nearly every year associated with Golden algae. This is obviously a major problem that fishermen are aware of due to the number of calls we receive concerning sick fish or fish with strange sores on them. Which is good, if you see something or think something is out of place don’t hesitate to call, that’s what we are here for. I thought about writing this article after answering such a call recently, and figured it would be good to go over some things concerning fish health that may be observed while on the water.

Diseases can be lumped into two categories, noninfectious and infectious. Noninfectious diseases are disorders that are linked to poor water quality or environmental conditions. Infectious diseases are caused by living things that parasitize fish or infect them. Usually an infectious disease is linked to a noninfectious disease or an environmental condition that makes things worse.

Fish can often fight off a disease through their natural defense system just the way people do. Most often environmental conditions are the difference between a healthy fish, sick fish, and ultimately a dead fish. In other words disease causing organisms are always present in a fish’s environment and there are conditions that must be present that stress the fish to compromise their overall health or conditions that are favorable for the disease to spread.

Most fish diseases have an ideal temperature for it to grow and become more virulent (ability to cause disease). This causes seasonal occurrences of certain diseases and given the water temperatures at the time of a disease incident gives specialists an idea of what to look for. Largemouth bass virus that killed many bass in Sam Rayburn is more likely to cause death at water temperatures at about 85 degrees. Usually when diseases like this hits it will make itself known then disappear as water temperature increases or decreases. Warm water usually is favorable to bacteria and parasite infections while cooler temperatures are more likely to produce fungal infections. Most diseases will not do much harm unless the fish is sick or unhealthy already, which is like adding insult to injury. Some things other than temperature that can make a fish weak and open to disease are stressful events such as spawning, poor diet, wounds, etc…

So what are some things to look for when deciding if a fish is sick or not? The first thing to look for is to see if the fish is acting strange. If the fish doesn’t spook easily or is swimming erratically are both good signs that something is wrong with the fish. The fish themselves will have sores or other things wrong with their appearance that will indicate that a problem may exist. Physical signs to look for are:

· Skin lesions or sores – These signs are an indication of several infectious diseases. Skin sores can be caused by bacterial infections or parasites.

· Reddish fins – Reddish fins with sores near the base of the fin are often associated with bacterial infections.

. Abnormal skin coloration – This can be caused by several things. Parasite infestations may cause the fish to produce a heavier than normal slime layer. Poor water quality can cause the fish to become anemic (the blood doesn’t carry much oxygen) that can discolor the skin.

· Abnormal appearance of the gills – Gills that are brown are associated with poor water quality and again is linked to anemia (not much oxygen in the blood). Swollen gills can be a sign of a parasite infestation. Sometimes toxins in the water will damage the gills.

· Swollen belly – Make sure the fish’s belly isn’t swollen due to food in the gut. Swollen stomachs indicate the body cavity is full of fluids. Swollen bellies are usually due to viral and bacterial infections.

If you suspect that fish are sick you can give TPWD a call to investigate. It is important that diseases be properly identified if we are able to treat the problem. Live fish with symptoms are best to submit for diagnosis. Try to collect at least a few fish to submit. Live fish are best to collect because tissues rapidly break down after death and bacteria will colonize dead tissue making identification of the problem difficult. Place the fish in a bag with no water in it and then place the fish in ice (cover the fish with ice). Do not freeze the fish, because this can cause cells to burst and kill parasites that may be the problem to be identified. Usually fish that are caught by fishing are pretty healthy, sick fish often will not feed. If you are unsure what to think or do, like I mentioned before simply give TPWD a call.

As always, if you should have any questions concerning this article or have any other fishery questions please don’t hesitate to contact me at This e-mail address is being protected from spambots. You need JavaScript enabled to view it or call me at 409-384-9572. Good Luck and Good Fishing!

Dan Ashe is a fisheries biologist with Texas Parks and Wildlife Department. He has worked out of the Jasper, Texas field office since 2005 helping to manage east Texas reservoirs including Sam Rayburn and Toledo Bend. Dan has also worked as fisheries biologist in Puerto Rico, California, and Alaska but now calls Texas home.