Exotic Aquatics: Life and Death

With the recent surge in reports of various species of non-native fish being caught in small lakes near or inside in populated areas, I think it's time that we start thinking critically so that we can act responsibly on the waterways we enjoy. Non-native species are a hot topic these days, and one that I'll cover again and again; for the moment, I'll speak on the specific issue of two common sources of conscious and intentional release of non-native aquatic species.

Interestingly, both of these sources of exotic species-release originate from people with highly benevolent intentions, at least as far as the release is concerned. The pervading reality following the release, however, is anything but positive in a number of ways and is a matter of education; in that education is a dose of prevention.

Source #1: Hobby Aquariums
This is a hugely popular passion/hobby/interest of many, many people in the US. While the industry has seen a steady decline since 2004, it is still going strong and, in some markets, growing again. The bottom line here is that there are millions of fish kept as “pets” in American homes. That can be a dangerous statistic, even in general terms. Without going into dissertation-mode, there are a few species which are especially likely to go from aquarium to local pond. The Pacu, various species of Plecostomus and Oscars all grow very quickly and to sizes that are unusually large for the typical home aquarium. Here are a few scenarios that I've run into:
  1. Sally is a second grade teacher who just bought a 10 gallon tank for her classroom, chooses the active and interesting-looking Pacu and is totally unaware that within months the fish will have outgrown that 10 gallon tank. In fact, that fish, if properly kept, can easily grow to 20 pounds and some to 60 pounds. On her underpaid budget, she can't afford to upgrade tanks and by the end of the school year is met with a huge fish in a tiny tank with no way out.
  2. Jerry, who has a 20 gallon tank that is in need of a bottom-dweller, becomes infatuated with the look of the “Common Pleco” and buys two. Unfortunately, he is unaware that many different species are sold under the name “Common Pleco” so 1) he isn't really sure what he's getting and 2) doesn't know that most of those species grow quickly to upwards of 24”. He soon realizes that these two fish are leading to overcrowding in his medium-sized tank.
  3. Brett, the freshman at Mizzou who got a 5 gallon tank for his dorm room and something to show off to friends, buys a single small Oscar. He loves the fact that he can drop a cricket in and see it get torn apart and swallowed as if he had a piranha. Unfortunately, Oscars are also notorious tank-outgrowers, growing 18 inches easily. The salesman at the petstore didn't know to recommend at 100 gallon setup for his fish, so was sent home with one 20 times smaller. After being fed with plentiful bugs and bacon by every visitor, “Oscar” is now unable to swim inside the tank.

These are, of course, only examples of fishing outgrowing their tank. There are just as many examples, if not more, of people getting in over their head, overpopulating, or simply losing interest and having a sudden “surplus” of fish about which, they really don' know what to do. In any scenario, many times the result is a fish released from it's aquarium into a local streamway or pond-lake. It is, after all, better than killing it...right? Wrong.

Source #2: Fishermen and Live Bait
It's no rare sight to see a fisherman sitting bank-side watching dutifully over his quarry of multiple poles, each armed with a live minnow. If he is an experienced fisherman at all, he'll know that bait gets stolen or swims off; to replenish his hooks, he has a bucket well full of healthy little Rosy Reds or small goldfish, each ready for action at a moment's notice.

The problem does not come from the use of live minnows as bait; most of them either get eaten or die from the wounds inflicted by being baiting onto the hook. The worst harm these fish can do is introduce parasites and/or bacteria that is foreign to that water, otherwise they simply become fodder for catfish or turtles. That is fairly harmless; it's not ideal, but fairly harmless in the relative grand-scheme.

The harm comes at the end of the fishing. The fisherman has bait left over that he now feels responsible for out of some paternal instinct. What was just moments ago gut-hooked and offered for bait is now tugging on his conscience like an orphan out in the rain. What to do with the 16 extra minnows? Releasing them into the same water that he's been tossing them for the past 4 hours seems logical...right? Wrong.

Again, without going into dissertation-mode, there is a huge difference between half-dead bait and viable individuals that will fight tooth-and-nail to survive (wouldn't you?). In addition to the parasites and/or bacteria that they may introduce en masse into that aquatic environment, here is a whole school of young-adult fish that need to find food and shelter. Imagine if a busload of children (who possibly have Swine Flu) were to show up at your kid's cafeteria at lunchtime. What would result is: 1) food shortage, 2) infections and 3) a lot of territorial behavior. That isn't the peaceful, benevolent and happy ending that was imagined for the bait minnows or the native fish.

So what is the solution for unwanted fish, either from an aquarium or bait bucket? There are several options:

Relocation to another home or fisherman. Other fisherman may be happy to take the extra minnows and use them as bait or other aquarium hobbyists may take that too-big fish. Ask around. There are a lot of petstores, clubs, and other fisherman that could become an easy and live solution for those unwanted individuals. Obviously, this is the best option.

Euthanasia is really the only other option. There is some serious and wide-flung debate on the best and most human processes available for euthanizing a fish. Here's a quick summary:
  1. Freezing: This shouldn't be considered a viable option because of concerns of humaneness. Debates over the ability and degree to which fish experience pain will go on long after we all die, but what is a definite “known” is that freezing a fish (or any animal) causes ice crystals to form in the tissue long before death. Anyone who has had frostnip or frostbite knows that hurts, and it hurts a lot. Don't freeze a fish to kill it.
  2. Clove Oil (eugenol): Mixing doses of 400+ mg per liter of water is required, but it effectively puts the fish to sleep. A kill-method is still required, but at least the fish is “out” for it. This is a widely agreed-upon humane method.
  3. Blunt-force trauma (“BFT”): Another widely agreed-upon method for humane euthanasia, this entails any number of options that are all fairly gruesome and must include destruction of the brain.
  4. Decapitation: This is acceptable for large fish or fish that you can handle well and complete the decapitation in one attempt and quickly. Most agree that BFT is still necessary afterward to stop all brain processes, so some may shy away from this since it's doubly-gruesome.
  5. Carbon dioxide infusion: This is a difficult process wherein CO2 is run through the fish water, suffocating the fish quickly. It's fairly human, but complicated and typically not convenient. There is disagreement over whether or not Alka-Seltzer tabs accomplish this; the prevailing professional opinion is that it does not.
  6. Out-of-water suffocation: Taking a fish out of the water to suffocate is not a good option; most fish can live for long periods of time (sometimes hours), suffering as they slowly die.
  7. Flushing: This is probably the worst option. It introduces the fish and it's possible parasites/bacteria into the sewer system/waterway and even worse for the fish—entails a lot of suffering. Imagine throwing your lab down your septic system; it would be the same for a fish. It leads to a long, slow and very unpleasant death. Do not flush fish that are alive.
  8. Temperature Shock: This is introducing the fish to a “pot” of water that is either super-cooled (using alcohol) or boiling. The shock of being transferred to an environment that is a radically different temperature is almost instantly fatal with only momentary pain. This, surprisingly, is a good option.
You may be grimacing at the “good” options, since most of them are pretty gruesome sounding. If that is the case, then especially consider what it means to be a responsible “owner” or keeper of fish. If you are unwilling to do the necessary steps to ensure your fish do not become exotic and harmful residents of some local waterway, then you have no business having the fish in the first place. Hopefully, release is not ever necessary; you've done the important work to be an educated and responsible keeper such that you never have to go down that road. If it's bait that needs to be dealt with (and use by another fisherman is not an option) and you are not comfortable with any of the effective and humane methods of euthanasia, then you have no business fishing with live bait—choose another method. It's not fair to the species living in the pond/lake/stream to act in such a way that will definitely harm them because you are squeamish.

While the idea of the death of even a single Danio or Rosy Red minnow is truly regrettable and should be prevented at all costs, the death of that one fish becomes pale in comparison to the definite risk it poses to the native fish and other aquatic species living in the water into which it gets released. In some cases, certain exotic species so dominate a body of water that the only option to save that “water” is a total fish kill—every fish dies. In those cases, saving the life of one fish (because you couldn't bear to kill it) signed the death warrant for hundreds of others. Life is a balance, and the scales do not accommodate shaking.

So what can you do? Think twice about any live fish purchase, whether for an aquarium or bait. Come up with a plan and think through every possible outcome. Be prepared to euthanize, but act wisely to prevent it from ever becoming necessary. That local pond or stream does not want the fish you don't want. Spend the time and energy to be responsible for the life that is in your care, and the life around you that's affected by your choices. Ultimately, if you propagate in your mind and heart the conviction that “all life is precious,” you will automatically act with compassion, wisdom and conservation-consciousness.

Written by: Will King, The Riparian Corridor Blog


  1. Will, how do you feel about feeding it to the cat?

  2. I think that falls somewhere between decapitation and BFT, depends on the dentition of the cat and how hungry it is. Acid bath is low on humaneness, but if it keeps a Pacu out of your local lake...ring the dinner bell for Jingles.

  3. Very well written. I'm actually in the process of writing something about exotics myself. I make trips down to the Everglades down here in Florida every year to fish for them.

    How do you feel about established exotics that are now seen (for lack of a better term) sport fish? Such as Buttefly Peacock bass (which I know were purposefully introduced by the state), Oscars, Mayan Cichlids and others?

    What about those species that have shown no negative impact on the ecosystem...yet?

    We have these debates in all of my fisheries classes and they usually just end up going around in circles. I'm interested to know what others think though!


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