This Is One Of The Worst Things You Can Do With Your Pet Fish

You may have had the best intentions when you emancipated your pet fish into the nearest lake, but setting your overgrown or unwanted aquatic pet free into the ecosystem is about the worst thing you can do with it.

Such pet-dumping is one of the reasons that on Wednesday, officials agreed to begin pumping poison into the San Francisco Presidio’s natural Mountain Lake, which has long been polluted by lead; toxins from car emissions, motor oil and pesticides; and non-native species like dumped pet goldfish that can grow to be more than a foot long in a lake.

“We have done everything we could to get rid of the fish humanely,” Terri Thomas, director of conservation for the Presidio Trust, told the San Francisco Chronicle. “Nobody likes to use pesticides. We tried everything that we knew we could do. It’s the last alternative.”

Presidio trust wildlife ecologist Jonathan Young estimated there were thousands of the “little fish” in the lake and a few hundred sturgeon and bass. Those intruders, wildlife ecologists told The Huffington Post, are problematic for a number of reasons.

“The main issue with aquarium releases is that the non-native critters released into the environment interact with the original aquatic community, often competing with or preying on native organisms, which can lead to declines in the native species,” Stephanie Carlson, an assistant professor in the environmental science department at the University of California, Berkeley, told HuffPost. “There are also issues with potential disease transfer from non-native to native organisms.”

University of California, Davis, extension aquaculture specialist Fred Conte pointed out that aquarium pets introduce harmful remnants from their former homes.

“Aquarium water, goldfish bowls and fish mucus potentially carry spores of common aquarium plants such as Elodea, which can become overabundant in the body of water; and infestations of aquarium plants can cause millions of dollars damage to combinations of water ways, farm ponds and lakes,” Conte told HuffPost.

“Today it is someone’s pet goldfish, tomorrow it may be someone’s northern pike,” he said, pointing to a 2007 incident in the High Sierras’ Lake Davis, where pike illegally dumped in 1997 aggressively preyed on the native trout -- a major component of the area’s economy. Officials there released the same poison, rotenone, used in Mountain Lake.

Conte is skeptical about whether poisoning the lake will be effective.

“Even if people do not continue to sneak fish in, birds can reintroduce carp from eggs adhering to their feet, along with other organisms,” he said. “Carp are almost impossible to remove once introduced. If any part of the lake is wet, eggs can survive.”

The Presidio Trust, which is carrying out the eradication as part of a multi-million dollar effort to restore the lake, is taking steps to control what it can and is setting up an “amnesty station” at the lake shore where pet-dumpers can leave unwanted pets in a tank.

Otherwise, Carlson says, the best thing you can do with an aquatic pet is bring it back to the pet store. Conte, meanwhile, suggests giving it to a friend.