Cyprinodontiformes vivíparos e ovovivíparos

Livebearer Cyprinodontiformes

Aquariofilia > Libertação de espécies exóticas

Aquaristics > Exotic species release

















Exotic fish and aquatic plants release in the wild

Personalized from the original text from Nonindigenous Aquatic Species ( U.S. Geological Survey ) 

Don't release exotic fish
or aquatic plants in nature

Any plant or animal that is not native to your region is considered an exotic species. 

All most all aquarium fishes and plants available for sale in national pet shops are exotic and are imported predominantly from farms located elsewhere, but the original ones were collected out of Europe, specially in Central and South America, Africa, or Southeast Asia.

Each year, over 2000 species, representing nearly 150 million exotic freshwater and marine fishes, are imported just into the United States for use in the aquarium trade. 

Europe and Japan probably fallow this income, however on a different proportion.

A massive income of potential invasive organisms is a daily threat in those countries where aquarium is a popular hobby.

Most hazard species will not resist to the first winter lower temperatures here in Europe, but their impact on local ecosystem can be potentially dreadful for years after a single summer season.

Potential problems

Unfortunately, a number of exotic fishes are released into the wild each year.

Hobbyists may not be able to take their fish with them when they move, so relasing the pets in natural waters is a hypotetical fast and nice solution. 

Others simply may have lost interest in maintaining some species or the aquarium itself.

Fish may also be released if they outgrow the tank capacity or if they appear to be in poor health. 

Whatever the reason it can be considered, releasing exotic fish and aquatic plants into local waters is not a good idea at all.

As in many other countries, in Portugal that it is an illegal practice .

You can read from the published document on the legislation issue all the details, ( unfortunately still only in Portuguese by now ). 

But there are sound biological reasons, too. 

Released fish will be physiologically stressed upon introduction to a different environment.

These newly unconfined animals will be susceptible to parasites and diseases from the wild or can pass on fatal unknown pathological agents to the new ecosystem.

Native predators such as larger fish, fish-eating birds, or water snakes and mammals that prey on fish might attack them.

For the environment it can be dramatic.

If exotic species can survive and reproduce, once establish they are difficult, if not impossible to control or eradicate.

Invasive plants and animals are a major threat to natural ecosystems and their species, second only to direct destruction of habitats by humans.

Non-indigenous aquatic plants can become a pest out of control in no time. They can colonize water bodies, competing for space and light, eliminating original aquatic flora and alter radically the environment. 

Floating aquatic plants, for instance, can grow as much as limiting boat traffic, swimming and fishing, preventing light and oxygen from reaching the water column. 

Introduced fish often cause changes in the existing aquatic original faunal makeup and food chains, through competition with native species or predation on them, as well as through overcrowding or aggressive behaviour.

They may contaminate native fish with exotic parasites or diseases to which local fauna isn’t biologically prepared to respond against.

An exotic may also affect the genetics of native species by hybridizing with them in the presence of close species.

Even the simple relocation of a few individuals from one hydrographical basin to another, inside their natural distribution, can cause harm to the gene diversity of the entire population.

Sole species may pose a physical or public health threat, such as some rare freshwater dangerous and noxious introduced fish.

Current situation

Currently, in Portugal there are 14 introduced freshwater species for a total of about 57.

In many other European countries the situation is far from be very dissimilar.

On the other side of the Atlantic, at least 185 different species of exotic fishes have been caught in open waters of the United States, and 75 of these are known to have established breeding populations. Over half of these introductions are due to the release or escape of aquarium fishes. 

Because many of these fishes are native to tropical regions of the world, their thermal requirements usually prevent them from surviving in temperate areas.

In the U.S., therefore, most introduced fishes have become established in Florida, Texas, and the Southwest. Examples include a number of cichlid, ( Cichlidae Family ) and livebearer Cyprinodontiformes, such as Swordtails (Xiphophorus helleri ), Platies ( Xiphophorus maculatus ) and Mollies ( Poecilia sp ).

The goldfish, a native of China, is one of the few examples of a temperate aquarium species that is established throughout the U.S.

What can someone do to avoid introductions ?

Alternatives to release, avoiding subject the fish to potentially harmful environmental conditions or risking prospective remarkable ecological and dreadful consequences are not very widespread yet, but there are optional means for disposing of unwanted pet fish.

Merely as a starting point there are a few possibilities to take in consideration while dealing with healthy fish too numerous or too big for the aquarium. One last hypothetical reason can even be those fish viewed as discarded pet as well.

In any of this odds here are some potential solutions :

a) Return it to a local pet shop for resale or trade.

b) Give it to another hobbyist, an aquarium in a professional office, a museum, or to a public aquarium or zoological park.

c) Donate it to a public or private institution, such as schools, hospitals, prisons, enterprises, clubs, fire departments and other places where aquariums are kept.

If these options are not available, or fish are agonising and perception of recovery is almost null, a veterinarian or fishery biologist can euthanize it ( put it to sleep ) with anaesthetic.

You can also do this at home by placing the fish in a container of water and putting it into the freezer. 

Because cold temperature is a natural anaesthetic to tropical fishes, this is considered a very humane method of euthanasia, while doesn't work well with all species.

Some pet shops also may be able to assist you if euthanasia is the option you choose.

Feeding other piscivorous fish with live prey is an ultimate option that many persons are reluctant to accept when time to deal with unwanted fish arises.

An excellent discussion of fish euthanasia was published in the September 1988 issue of Tropical Fish Hobbyist. This magazine is probably not very easy to find outside the United States, but it may be available through pet shops or at your local library with luck. 

If you must give up your pet fish, please consider its well-being and its potential impact on the environment. 

Do not release exotic fish and plants into a natural body of water or even to an artificial water environment. In the most unsuspicious places there is still a continuous risk of late dispersal to the wild by countless ways, without disregard even human action.

Back to top


Optimized for 1024 x 768 resolution

© 2006 - 2011 All Rights Reserved 

e-mail :

- Data and information authored and produced on this website are in the public domain.

While the content is in the public domain, some pages contain images and material that are copyrighted by others and used here with permission.

Such information is available for private use, study or research. You should obtain permission from the copyright owner for other uses. Please carefully examine all the content and all linked pages for copyright restrictions and to secure the necessary permissions.

Content accuracy and usability of data and information - Every effort is made to provide and maintain accurate, complete, useable, and timely information on this website. However, some data and information accessed through these web pages may, of necessity, be presented prior to final review and confirmation.

These data and information are provided with the understanding that they are not guaranteed to be correct or complete. Users are cautioned to consider carefully the provisional nature of these data and information before using them; such data and information are the singular responsibility of the user.