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Myths About Trout and Slime Removal

Throughout the trout angling community there is a pervasive belief that you need to be careful not to harm a trout's skin or remove its slime otherwise it will develop a skin infection and die. This is a myth whose death is long overdue. Fact of the matter is, it is extremely unlikely for a trout caught and released in the wild to develop a skin infection, much less die from it, regardless of how it is handled.

Above is a brown trout with a skin infection from pathogenic Saprolegnia, the main cause of skin infection among trout. As you can tell it is very visible.

Causes of Trout Mortality

I am aware of 4 studies conducted between 1980 and 2005 indicating the causes of trout mortality due to being caught and released by anglers and none of them mentioned skin infection. One was done in Alberta Canada, one in the upper Midwest Driftless area, and the two others done elsewhere in the USA. They all agreed on the following points:

1. The mortality rate for trout ranged from 1.5% to 3% with 2% being the general average.

2. The main cause of death by far was lactic acid build up (exhaustion).

3. The second main cause of death by far was hypoxia (oxygen deprivation).

4. The third main cause of death was use of natural bait.

5. The remaining causes of death were attributed to various factors such as barbed treble hooks, dropping fish, shaking fish, squeezing fish, damage to the gills, eyes, or internal organs.

Once again, none of those studies found slime removal or skin infection to be a factor. I would like to point out that these studies were generally conducted with average fishermen during the peak fishing season. During that time the water temperatures tend to be moderate and the size of fish tends to be modest. Both of those qualities help to contribute to a low mortality rate of around 2%. On the other hand, most of the people releasing the fish were not fanatically obsessed with careful handling of the fish as can be indicated by issues such as shaking fish off the hook or using bait or barbed treble hooks. This would tend to increase the mortality rate. Also to be noted is that the majority of anglers participating in these surveys used artificial lures. Studies have shown that fish caught on live bait can have mortality rates of up to 84% (Hunsaker et al., 1970).

Susceptibility to Infection

A study was done by Schwabe et. al and published in the 2014 Vol 34 issue of the North American Journal of Fisheries Management (p. 1221-1226). 137 rainbow trout were caught with a fishing net and briefly handled so as to simulate actual fishing conditions and then placed in a tank and observed for 2 weeks to see if they developed any skin infections. To make matters more interesting the tank was deliberately contaminated with the main nemesis to a fish's skin: potentially deadly Saprolegnia zoospores. This pathogen causes a white fungus to grow on the fish's skin and can lead to death. It is found the world over and is probably the most common serious threat to fish in terms of skin infection.

The result was rather interesting. Of the 137 trout put in the tank only one died but it had nothing to do with skin infection. In fact, none of the trout became infected. It is interesting that in one of the articles I read for researching this matter it actually cited the above study to support the belief that loss of mucus from handling during the catch and release process can make a trout more susceptible to skin infection. However, the article actually shows that there is no evidence for such a belief.

Wetting of Hands

Since I began posting videos about trout streams I have had lots of people tell me that I should wet my hands before touching the fish. I understand this has been repeated many times in the outdoor media and believed by a majority of anglers but it is a complete myth. As far back as 1980 scientific studies have shown there is no correlation between wetting your hand before handling a trout and whether or not that trout lives or dies. Such an experiment was published by P.J. Hulbert and R. Engstrom-Heg in vol 27 of the New York Fish and Game Journal. A similar experiment was done in 1987 by Hegen et. al and published in the Annual Conference Association of Fish and Wildlife Agencies, vol 38, p. 488-494. Again, both studies have shown that wetting your hands prior to handling a trout has no impact on whether that trout lives or dies. There are reasons which I discuss in another article as to why the outdoor media refuses to mention these findings. Yes, there is a coordinated conspiracy in the outdoor media!

There was another study done by Teah W. Lizee et. al, 2017, regarding brook trout in the state of Maine. This study concluded that attempting to land a brook trout using wet hands resulted in the fish being dropped 4 times as often as when a net is used. This study specifically recommended NOT using wet hands when attempting to land a trout. In my experience this is very obvious. I should also point out that brook trout are probably the easiest fish to hold because they tend to be small. Brown trout and rainbows are usually bigger and cutthroat trout are the most slippery. As discussed at the beginning of this article, dropping of fish was cited in several studies indicating the cause of trout dying whereas skin infection due to mucus loss was not indicated. In fact, despite extensive research I have yet to find any published scientific report of a trout dying due to skin infection resulting from being handled by an angler.

Nets

Many people have told me that if I use a net it should be a rubber one so as to not damage the fish's skin. Once again, there is an incorrect assumption here that damaging the skin or removing some mucus from a trout's skin would make it susceptible to skin infection and then death. While I hope at this point I have convinced the reader this concern is unwarranted, let us consider the effect nets have on trout.

There are 3 basic types of nets used by trout anglers. Traditional nets are usually made of polypropylene with sparse webbing and bulging knots at the point of mesh intersection. Standard trout nets are typically wooden, small, lightweight, and have a smooth nylon mesh with dense webbing and no knots. Often the mesh of these nets is somewhat thick with a cushioning quality to them. Lastly there are rubber nets designed to satisfy the conscience of those trout anglers who have bought the concern expressed by the outdoor media that you need to be very careful to avoid removing mucus from a trout's skin to prevent infection and death.

I have had some concerned viewers tell me of a study they read showing the harm non-rubber nets were doing to fish. I believe this article originated from research by Colotelo and Cooke in 2011 involving Northern Pike and was then summarized in the outdoor media. There were photographs of scars on the skin due to the net. These fish were kept in tanks to see what the long-term effects were. It appears the long-term effect is that the fish have a scar that remains visible for some time. Hopefully these fish weren't planning on having an acting career. I wonder if these people were aware that if these fish were to grow to trophy size and get caught and mounted that the taxidermist is going to just paint over the scar so it will not be seen when hung on some proud angler's wall. The main point is that while the non-rubber net may have scarred the fish it did not kill the fish or prevent it from growing to a larger size. The second point to take from this study is that the comparison was unfair because it compared a rubber net to a traditional net and left out standard trout nets. Most trout anglers who wade use traditional trout nets (including myself). A traditional trout net is not going to leave any marks on a fish's skin. I believe this article, or at least the summary as published by the outdoor media, was deliberately biassed towards rubber nets and I wouldn't be surprised if there was either direct or indirect compensation for the article by the companies that manufacture rubber nets.

A more comprehensive study about nets specific to trout was done by Teah W. Lizee, A.J. Danylchuk, Lian Nowell and Steven J. Cook and published in the north American Journal of Fisheries Management vol. 38, 2018. This study considered all 3 types of nets used for trout fishing. It found a serious flaw with rubber nets in that the wider gap between the mesh caused fin injury, fin fraying and damage to connective epithelia. No such mishaps were observed with standard trout nets.

One interesting observation from the above mentioned study was that they actually quantified the amount of mucus removed by the various types of nets. This was described in terms of proportion, with rubber nets removing a proportion of 0.07 of mucus from a trout. The other net types removed up to 0.3 proportions of mucus. For comparison, bare wet hands removed 0.2 proportion of mucus from trout. Of course this study in no way found any correlation between mucus removal, skin infection and mortality in regards to trout. Unfortunately, the outdoor media has used studies such as this to emphasize the importance of using rubber nets for trout under the false premise that mucus removal results in fish mortality. It does not.

Observations of Jay Thurston

Jay Thurston is a master trout angler, author of 3 books on trout fishing and a person I had the privilege to fish with once. The guy was out fishing me so badly I decided to put my rod away and just film him as he caught fish after fish. On August 13, 2014, Jay wrote in the La Crosse Tribune that during his years of fishing he had caught enormous quantities of trout and yet never once observed one with a skin infection. I should point out that Jay had a college degree in Geology, so like me (Physics) he was a trained scientist. For most of his life he meticulously recorded the length of each trout caught, the time, water temperature, and lure used. When I fished with him on Wisconsin's Pine River I observed him looking each trout over quickly but carefully before releasing it.

You might think that maybe skin infections are difficult to notice. I don't think Jay would agree with you. He once took a tour of a fish hatchery. At the hatchery he could notice small patches of white fungus growth on the skin for some of the trout. This was mentioned in his article and offered as an explanation as to why some biologists who work for state department of natural resources warn anglers to take care in not removing slime from trout.

Immune suppression in fish hatcheries is not uncommon. Studies from Mazeaud et. al in 1977 show that chronically stressed fish tend to be less disease resistant as a result of a weakened immune system. The same is probably true for people. Fish hatcheries tend to have high levels of ammonia and nitrates in the water and that can stress a fish. Those types of water imbalance can be difficult to correct, especially for fish hatcheries that rely primarily on recycled water. I once had a fish tank with gold fish in it, a very hardy fish. My filter was not working as well as it should and a water chemistry imbalance resulted in the same type of skin infection in the gold fish (white patches of fungus) that Jay saw in the hatchery. My goldfish died. These types of water chemistry issues generally do not occur in trout streams. Even in the Driftless Area of southwest Wisconsin where Jay did most of his fishing, where the streams are surrounded by farmland with manure spread on their crops and roaming cows and all of those fertilizers washing into the streams after rain, the water does not get contaminated enough to cause the trout to become susceptible to skin infection.

Observations of Dan Coppersmith

As of the moment I haven't fished as long as Jay Thurston and probably haven't caught as many trout as he has but I have still caught a lot of trout. Furthermore, I have fished trout streams all over the United States as well as Canada. Like Jay I always record the length of the fish I catch and especially since I got involved in film production I display the fish for the camera and so I take a good look at it. Never in all of my travels and catches have I observed a trout with a skin infection. I have seen many trout with a wide assortment of injuries. Some of these looked like they were inflicted by anglers, such as an injury to the jaw, while others appear to be wounds from otter or heron attacks. Even for the fish having an open wound I have seen no sign of infection.

Even when fishing warm water streams having a fair amount of pollution it is rare I see any signs of skin infection. Note that trout live in waters that tend to be cool and clean and not the best habitat to foster bacteria growth. Other fish species are often in waters that get considerably warmer and have more bacteria and these bacteria are considerably more active.


Brown trout with wound from heron attack. No infection was observed.	Brown trout with wound from otter attack. No infection was observed.	Carp with portion of tail bit off. No infection was observed.

Years ago I used to fish several warm water streams in southeastern Wisconsin for rough fish. I would fish until I caught about 60 pounds of fish and then stop because that is all the fish my cooler could hold. These included carp, channel catfish, bullhead, sheepshead, dog fish, redhorse and white bass. While these streams were monitored and the fish deemed safe for human consumption there was a lot of farm land in the watershed and a lot of manure ended up being washed into the rivers. This is one reason the streams were so fertile and produced so many fish. As there were few game fish present not many people fished the area. I do recall seeing one fish from that area that looked like it had a skin infection although it was not the white fungus that the angling world is so concerned about. And no, I doubt think the fish had been caught and released. Upon reviewing my pictures of these fish I don't see any examples of infection. Perhaps the fish was turned the wrong way for the photograph. The point is, even in streams having warm water, high bacteria levels and lots of fish the incidence of skin infection is extremely rare.

Trout Hatcheries

As mentioned previously, fish hatcheries can easy experience chemical imbalances that stress trout and make them susceptible to skin infection. What a lot of people don't know is the trout in a hatchery can also experience a tremendous amount of abrasion from concrete holding tanks. Concrete has a naturally abrasive surface, and unlike rocks that have been subject to stream flow and polished by chunks of floating ice or other debris for decades or centuries the only think polishing up the concrete holding tanks are the soft bodies of trout. I have caught stocked trout from Virginia to California whose tail fins have been eroded by as much as 70%. I have caught stocked trout whose pectoral fins have been reduced to little tiny stubs that appeared totally useless for swimming. I know these fish were recently stocked because these were streams that get fished out fairly soon after each stocking. I would assume the fins eventually grow back and appear normal looking although I don't know how long that takes.


Rainbow trout from hatchery, Robinson Creek, CA	Close up of tail.	Close up of pectoral fin.

The point of the matter is that we have a significant number of anglers, persuaded by the outdoor media, to be obsessively concerned about being gentle to not damage a trout's skin or remove its mucus, meanwhile many of the trout they are catching just came from a hatchery possibly having bad water and horribly abrasive holding tanks. If the trout survived the bad water chemistry and rubbing up against abrasive concrete while they grew to catchable size without getting a skin infection then I really don't think loosing a little mucus in a clean trout stream is going to cause them a problem.


Rainbow trout from hatchery, Back Creek, VA	Close up of tail.	Close up of pectoral fin.

Rainbow trout from hatchery, Back Creek, VA	Close up of pectoral fin.

Gloves

The last point I would like to bring up is the use of gloves. I wear a pair of sun gloves whenever I fish. These gloves have a synthetic leather palm and an outer side that dries quickly. They protect my hands from sunburn, abrasion, biting insects and stinging plants. I would advise every angler to consider wearing them. The gloves are sprayed with water and slime repelling additives to help reduce the amount of fish slime that adheres to them. To be honest I don't add those repellants for the sake of the fish. I add them because I don't like a lot of slime accumulating on my gloves.

There are many people who mistakenly believe every fish I touch while wearing gloves ends up dying. There have been many people who have insisted I stop wearing gloves when fishing. I have to congratulate the outdoor media for being so successful at misleading the general public. While no official testing has ever been done, I suspect the proportion of mucus removal while handling trout with gloved hands is probably comparable to that of a standard trout net.

My gloves give me a considerably better grip when holding a fish than using bare hands. There have been occasions when I have held a trout with bare hands and the difference in grip is incredible. When you consider that death by dropping and death by squeezing too hard has been consistently documented in trout mortality studies, where as death by mucus removal has never been documented, it continues to show just how out of touch with reality the outdoor media and general public is regarding this topic. I also find it disturbing that many anglers appear more concerned about the well-being of a fish than that of a person.

Conclusion

It is my hope that those reading this article will have come to the realization that there is no need to be concerned about trout contracting a skin infection and dying from it as a result of handling during the catch and release process. It is my advice that conscientious anglers focus on other factors that have an actual impact on whether the trout lives or dies and stop worrying about slime removal.

Most of all, it is my hope that all of those anglers who keep telling me I am killing trout due to skin irritation are redirected to this article, read it, and stop irritating me with such stupid concerns. This article has been written as a response to all of those concerning comments and I have nothing more to say on the matter. If this strikes a nerve in someone and they have a deep need to discuss it please consider there are 9 billion other people on this planet. Find someone else to discuss it with. The people with whom I have tried to explain this to have appeared totally close minded and incapable of an intelligent discussion. I am a busy person and if I have a few spare minutes in my day I would prefer to spend it playing beautiful, peaceful music on my guitar rather than telling some fanatic who just wants to show everyone how much they know and care that they are wrong.

Regards,

Dan Coppersmith 07/01/2024

Created by: Dan Coppersmith 2024| www.CoppersmithStudios.com

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Myths About Trout and Slime Removal