Lurking in the depths of a 40,000-liter fish tank within the Paris Aquarium in Paris, France, is an unlikely sight—one that many visitors might be surprised to see. The freshwater tank is just one of several that house the aquarium’s growing population of goldfish. Over the past few years, the aquarium has become a refuge for unwanted goldfish, to the extent that rarely a day goes by without a local resident dropping off an unwanted pet. At last count, the aquarium has more than 1,000 goldfish, 600 of which are rescues, and that number continues to grow.

The goldfish sanctuary began about four years ago when visitors started approaching former curator Guillaume Eveillard and his colleagues to ask what they should do with their goldfish besides flushing them down the toilet. (Yes, people actually do this, and no it’s not a wise choice.) Rather than force these pets to an untimely death, the aquarium began adopting them instead, with people bringing them to the aquarium in tanks, buckets or any receptacle they can transport them in.

Typically, parents would bring in goldfish after their children won them as prizes at local carnivals. But what starts out as a pretty pet often becomes nuisance for many people, since they're not quite sure how to properly care for them.

"I think that people who purchase goldfish aren't always well informed of the implications of having one as a pet and the space needed to raise one," says Eduardo Da Forno, aquarium manager at the Paris Aquarium. "They ususally just want to make their child happy, but they aren't realizing the living conditions these fish [need to survive]."

According to the aquarium, many Paris homes simply aren't large enough to house fish tanks equipped with filters that are the appropriate size for goldfish. Although goldfish may seem like one of the smaller species of fish swimming in circles in fish tanks, once they reach maturity in about five years’ time they can grow up to 16 inches in length and live up to 30 years in the wild, according to the aquarium. In small tanks, they typically top out at two inches long. (The oldest known goldfish to have ever lived made it to 45.)

The Paris Aquarium dedicates three tanks of various sizes to goldfish and their freshwater neighbors, including sturgeon, carp and bream. A number of breeds of goldfish are represented there, including lionhead goldfish and several types commonly found in Japan. Da Forno says that, to date, they've collected approximately 1,000 goldfish and plan to continue collecting them to help educate the public.

"The main goal of this program is to empower people and educate them about what it takes to have a goldfish in their homes," he says. "We want to raise awareness."

The goldfish sanctuary has proven popular with visitors, and become an educational resource for the aquarium to teach people about the harm that releasing them into the wild can do—to the environment, as well as to the goldfish themselves.

"Obviously it's better to donate the fish to the aquarium," Da Forno says. "That way they can continue their lives in an appropriate place instead of flushing them down the toilet, which equals death for them."

Not only that, but flushing them or releasing them into the wild can be bad for the environment, since that same water eventually makes its way into our local streams and rivers. If a fish has any sort of parasite or virus, the disease has the potential to spread to other species. Furthermore, the fish that survive the journey tend to reproduce quickly and compete with native species.

So the next time you go to a carnival, resist the urge to play a game where the prize is a goldfish. Winning a stuffed animal is a better option. But if you’re really deadset on having a pet fish, consider adopting a guppy. Their size at adulthood: a measly one inch.