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Invasive Fish and Plants




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I'm a huge fan of aquariums and ponds, but there is a darker side of the hobby that bears discussion. That "dark side" is the issue of dumping unwanted aquarium and pond fish or plants into local waterways. When an owner decides, for whatever reason, to get rid of their aquarium or pond, it is tempting to give their fish a new home at the local river. It's so easy to take those unwanted pond plants to the lake on the next fishing trip. While that might sound like an easy, and completely safe, way to deal with unwanted fish and plants, it can have a devastating effect on the environment.

Non-Indigenous Fish
It is quite common for aquarium fish owners to be faced with the dilemma of a fish they no longer want. Perhaps the fish was small when they purchased it and it grew much larger than they expected. Or it may have been more aggressive than expected, or didn't get along with other fish in the tank. There are man reasons that can prompt a fish owner to ponder ways of ridding themselves of a fish. Regardless of the reason for wanting to get rid of a fish, there are two options that should never be pursued. Those are flushing the fish in question, or dumping it in a local waterway.

Nile Perch
Fish that are not native to a stream, river or lake, can have an extremely damaging effect on the local habitat. This is particularly true if the fish is aggressive and has no natural predators. An aggressive, or even a large, non-indigenous fish, can quickly kill off the native fish, or out-compete them for food sources. In some cases this can result in the extinction of an entire species. One of the worst cases of this happening, was the introduction of the Nile Perch into Lake Victoria in Africa. Initially introduced during the 1950s for the purpose of commercial fishing, there was no thought to the effect this would have on the habitat. The native fish were no match for the much larger Nile Perch, which quickly wiped out many local species of fish. Although some species returned, dozens of Cichlid species that were found only in Lake Victoria, were lost forever.

In the United States the introduction of the highly aggressive Snakehead into local waterways is yet another example of the damage that non-Indigenous fish can do to native habitats. The fish first hit the news when specimens brought into the country as a food fish, were dumped into a pond in Maryland. Those fish reproduced voraciously and spread to nearby waterways. Eventually the Northern Snakehead established itself in the Potomac River, where it has no predators to keep it in check. In addition to eating many of the native fish, the Snakeheads also compete with some species for the same food sources.

Although not as often seen in the news, the Asian Carp is perhaps the most widespread of all non-indigenous fish in the United States. Introduced in the 1970s as a means to eliminate unwanted algae in ponds, they eat anything in sight. Having already taken over huge areas in the Midwest, there is concern that the Asian Carp may reach the Great Lakes region and cause irreversible damage there. Freshwater fish aren't the only problem. In Florida the Lionfish, which are not native to ocean surrounding the state, have significantly reduced local fish populations in some areas. Some lobster fishermen have reported catching hundreds of pounds of Lionfish daily.

However, even seemingly non-threatening fish can damage the native habitat. Goldfish are quite often dumped in local waterways. Clearly they are not aggressive, but they are voracious eaters of the vegetation. That means there is less food for other veggie eating fish, and even the meat-eating fish are impacted, as many of them use vegetation for shelter and breeding. Many other aquarium fish have established themselves in non-native waterways. A few of them are:
  • Goldfish - Carassius auratus
  • Jack Dempsey - Rocio octofasciata
  • Jewel Cichlid - Hemichromis sp
  • Lionfish - Pterois volitans
  • Mayan Cichlid - Cichlasoma urophthalmus
  • Mosquitofish - Gambusia affinis
  • Snakehead - Channa argus
  • Texas/Rio Grande cichlid - Herichthys cyanoguttatus
  • White Cloud Mountain Minnow - Tanichthys albonubes
All of the above fish were introduced by aquarium owners who either didn't realize, or didn't care, that habitat damage would occur as the result of dumping aquarium fish. The bottom line is that aquarium fish should always be kept in an aquarium, never set free into the local habitat.

Non-Indigenous Plants
Non-indigenous plants can be just as damaging to local habitats as fish. They compete with native plants for nutrients, thus reducing or eliminating the local vegetation. Often they promote massive algae overgrowth in ponds and lakes, which in turn causes a cascade of damage to the habitat. Some of the most damaging species are popular aquarium and pond plants. Those include:
  • Brazilian Waterweed - Egeria densa
  • Eurasian Watermilfoil - Myriophyllum spicatum
  • Hydrilla - Hydrilla verticillata
  • Water Hyachinth - Eichornia crassipes
  • Water Lettuce - Pistia stratiote
  • Water Lilies - Nymphaea odorata
Some of these plants are almost impossible to eradicate once they take hold in a pond or lake.

What To Do
The key thing to remember is never dump an aquarium fish or plant in a pond, stream, river or lake. If you have unwanted fish or plants dispose of them in safe ways. There are more options than you may realize. Consider these possible ways to get rid of a fish your plant you no longer want.
  • Give them to a local pet shop
  • Donate then to a public aquarium
  • Donate them to a school, nursing home, or medical office
  • Place an ad for a free fish/plants in the newspaper
  • Donate them to an aquarium club
  • Give them to a friend with an aquarium
  • Compost or burn unwanted plants
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