LOS ANGELES, CA (Catholic Online) - "During these surveys, we've found a nice corner where there's about 15 other goldfish," environmental scientist Sudeep Chandra of the University of Nevada says. "It's an indication that they were schooling and spawning."

The fish were probably dumped by aquarium owners. It's not yet known whether the giant fish were introduced as fully grown adults, or while they were still small. Even a small creature can have a big impact, if there are enough of them.

"The invasion is resulting in the consumption of native species," Chandra said. Scientists have noted that the goldfish are just one of several species of invasive warm-water fishes in Lake Tahoe. These types of fish excrete nutrients that cause algal blooms, which threaten to muddy Tahoe's clear waters.

Aquarium dumping has become a common practice in the United States and elsewhere, and it's taking a toll on native wildlife. A recent report on California's aquarium trade found that fish owners and importers are introducing hardy, nonnative aquatic species to California waters.
 
Scientists know that the practice of aquarium dumping is occurring because these species could not have ended up in these waters naturally. Between 20 and 69 percent of fish keepers surveyed in Texas admitted to dumping, according to Williams.

Other ways that invasive species find their way into natural ecosystems include aquaculture, live seafood, live bait, and fishing and recreation vessels. More than 11 million non-native marine organisms representing at least 102 species arrive at ports in San Francisco and Los Angeles alone.

The worst invaders include tropical fish, seaweed and snails. An example of one of the worst and most costly invaders was deadly type of seaweed known as Caulerpa, a type of algae that produces toxic compounds that kill off fish. Caulerpa was eradicated in 2000, at great expense from lagoons in Southern California.

Aquarium owners should be more careful when disposing of unwanted fish and other animals, Williams cautioned. "It's pretty simple: Don't dump your fish," she said.

Scientists suggest calling the pet shop that sold the fish or your state department of fish and wildlife. While euthanasia is another option, but simply flushing fish down the toilet can be problematic - for the fish and for your plumbing.

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