According to an article published by the American Institute of Biological Sciences, a total of 138 alien fish species have been introduced into the United States (Courtenay, 1997). Forty-four native species of fish are threatened or endangered by alien-invasive fish (Wilcove and Bean, 1994). An additional 27 native fish species are also negatively affected by introductions (Wilcove and Bean, 1994).  Nearly 100 aquatic invertebrate species have also been introduced.

Invasive Fish “Set Free” by Their Keepers

The excuses for releasing pet fish and invertebrates into the wild are endless, but none are good enough.  As aquarists, we have to accept responsibility for the lifetime of fish, snails and shrimp we obtain, regardless of size, aggression, or a change in personal circumstances.  Aquatic pets released into the wild can cause serious, long-term damage, and it simply is not an option for unwanted pets.

The most serious consequences of releasing fish and other aquatic pets into the wild are the spread of disease and the risk of them becoming an invasive species. Introduced fish species may also hybridize with native species and they frequently alter the ecology of aquatic ecosystems. Some species of aquatic snails can multiply and mow vegetation at alarming rates.

Of course, aquarium and pond hobbyists aren’t the only people to blame for invasive species, and some might argue that it’s just easier to point the finger at them as the problem.  In reality, aquarium enthusiasts are usually more aware and concerned than others when it comes to environmental impact.

Other culprits:

  • While the government is now more aware of the consequences of actions such as fish introduction for bio-control, that hasn’t always been the case.
  • One of the biggest offenders are ships coming into our ports.  It is estimated that every single day, ship ballast water distributes over 10,000 alien species around the world.  In fact, at least one third of the Great Lakes alien species is attributed to ship ballast water.
  • Fishing can introduce bait or transfer species from one body of water to another.
  • The weather can transport and introduce species through hurricanes, floods, etc.

Fish-keepers are to blame for a portion of the problem, however, and it is our responsibility as a group to both refrain from the practice and to educate other hobbyists. It’s also the law.  We must also be aware that introducing fish to ponds which are native to our area in another location can still have a negative impact.  Ponds also pose a risk of wild introduction via birds, raccoons and the weather.

If you don’t care about the environmental impact, at least think of the impact on our hobby.  Do you want fish keeping to be so heavily regulated that we need permits to own and ship any fish that may survive our climate?  It can, has, and will happen if we don’t take responsibility, address the issues and most importantly, educate other fish-keepers.

Wild Release of Aquarium Fish

Is it really a problem for cold climates like Canada?

While most of the introduced fish and invertebrates in the US are in warm climates, there are several species of fish commonly kept in aquariums that can survive cold climates as well.  In the Great Lakes alone, there are over 160 introduced species of plants, fish, crustaceans and plankton.  Yes, it is a problem, and it’s a big one.

Dr. Hugh MacIsaac, director of the Canadian Aquatic Invasive Species Network (CAISN) states “Invasive aquatic species are changing the appearance and function of our ecosystems. In the Great Lakes, there is a new invasive species happening every seven months.”

According to a report filed by MacIsaac, 18 identified invasive species have an economic impact of $13 to $34 billion.

Some aquarium fish species that may survive a cold climate include Goldfish, Koi, some Catfish and Minnows.  Even if the fish we introduce cannot survive a cold climate, they can still introduce disease or hybridize with native species.

What can aquarium hobbyists do?

  • Keep it in tanks or euthanize it.  You may be able to find a new home through classifieds, your local fish club, stores, or schools and other public aquariums.  If you cannot find a good home or return the creature to the store, you must humanely euthanize.  Consider it a lesson learned the hard way.  NEVER, under any circumstances, release aquatic pets into the wild.
  • Research!  Find out about aquatic pets before you purchase them.  Be aware of their size, aggression levels and breeding habits to make sure you can accommodate them for their entire lifespan. Remember that large fish are very difficult to find homes for and don’t assume you’ll be able to do so.
  • Educate fellow hobbyists in a friendly, informative manner.  Share information and educational materials through online communities, pet blogs, and aquarium clubs.  It’s a fantastic fish club meeting topic for which you can have speakers and educational materials.
  • Encourage your local fish clubs and stores to get involved (resources below).
  • Work with the authorities and conservation groups.


There are many websites that offer information about invasive aquatic species and we’ve included two of them below.  Some also offer free materials and printable documents for you to distribute.

Keep Our Lakes Great

As aquatic pet keepers, let’s be part of the solution instead of part of the problem! Do you have tips or suggestions for how we can help? Please add them in the comments below.

Pimentel, David.  Environmental and Economic Costs of Nonindigenous Species in the United States. Bioscience, Vol. 50 No. 1.

You May Also Be Interested in Reading:
Welfare Weekend: 3 Groups Of Fish That Are Cruel to Keep in Your Aquarium


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14 thoughts on “Welfare Weekend: Wild Release of Unwanted Aquarium Pets ©

  1. I don’t know how anyone can be so cruel to fish but they don’t seem to matter to anyone. Your article is a very pleasant breath of fresh air and I anticipate enlightenment by all who read it.

  2. So important to be responsible fish people and report people when they’re not before they ruin it for everyone else.

  3. And that’s only the species we know about, there’s probably a lot more invasive species.

  4. Someone let goldfish go in a pond where I grew up and they were so big that my dad thought they couldn’t be goldfish. I can understand how they can take over.

  5. Yes! This topic isn’t talked about enough and how can fishkeepers know about it if we don’t tell them??? SPREAD THE WORD!!!

  6. I saw a big Chinese algae eater in a stream by Burn’s Bog once so I can tell you at least one aquarium fish survives in Canada.

  7. A few can ruin it for everyone else. Thanks for educating people. A fish club night about invasive species is a great idea, I’m going to arrange one.

  8. There’s goldfish in our local river and it makes me so mad every time I see one. They can cause so many problems and should be banned from sale.

  9. For a long time I didn’t know that letting fish go wild would cause any problems. Thank God for the internet, it sure helps spread the word.

  10. Great coverage of an important topic. I agree that fishkeepers aren’t the biggest offenders but they contribute to it. I recommend covering ponds during bad weather and at night to keep them contained.

Comments are closed.