If you have pet fish you can no longer keep, you have several good options: rehome them to another fishkeeper, surrender them to a local aquarium society, return them to a pet store, or, as a last resort, euthanize them humanely. The one thing you should never do is release them into local waterways. Even a single aquarium fish dumped into a pond or stream can trigger serious ecological damage.
Why You Should Never Release Fish
Releasing aquarium fish into lakes, rivers, or storm drains is illegal in many states and environmentally destructive in all of them. The global ornamental fish trade is a multi-billion dollar industry, and it has been responsible for introducing countless non-native species into ecosystems where they don’t belong. Once established, these fish can outcompete and displace native species, alter water chemistry, and collapse local fisheries.
The scale of damage can be staggering. Pleco catfish, one of the most common aquarium species, have invaded rivers across the southern United States, Mexico, and Southeast Asia. In one river in southern Mexico, introduced plecos reached a density roughly 160 times greater than the native fish population. Their sheer biomass fundamentally rewired the river’s nutrient cycle, flushing nitrogen into the water at 25 times the rate of native fish while locking up phosphorus that other organisms needed. In several Mexican states, pleco invasions have decimated freshwater fisheries that local communities depend on.
Goldfish, oscars, and snakeheads are other frequent offenders. Even tropical species that seem unlikely to survive a cold winter can establish breeding populations in warm-water outflows near power plants or in southern waterways. Flushing fish down the toilet is equally harmful. It’s not a humane death, and in some plumbing systems, fish can survive and reach open water.
Rehome to Another Fishkeeper
Your best option is finding your fish a new home. Start with the people closest to you: friends, family, coworkers, or neighbors who already keep aquariums or have expressed interest in one. A fish that’s healthy and well-cared-for is an easy gift for someone already in the hobby.
If no one in your circle wants them, cast a wider net online. Local Facebook groups dedicated to fishkeeping are one of the most active marketplaces for rehoming. Post clear photos, list the species, size, temperament, and any tank requirements, and you’ll often find a taker within days. Craigslist, Reddit’s r/aquaswap community, and apps like Nextdoor are also worth trying. Many hobbyists actively search these platforms for specific species.
Surrender to a Local Aquarium Society
Most regions have local aquarium clubs or societies that accept surrendered fish. These groups hold regular meetings and auctions where members buy, sell, and trade livestock. Some, like the Greenwater Aquarist Society in the Midwest, have formal rehoming programs specifically designed to prevent owners from releasing exotic species into local waters. They’ll accept unwanted fish at meetings and find them new homes through their membership network.
To find a club near you, search for your city or state name plus “aquarium society” or “aquarium club.” Many are listed through the Federation of American Aquarist Societies directory. Even if you’re not a member, most clubs welcome surrendered fish, particularly unusual or large species that are hard to place through casual channels.
Return to a Pet Store
Many local fish stores (not always big chains) will take back healthy fish, especially desirable species they can resell. Call ahead and ask. Independent shops are generally more flexible than corporate pet stores, and some will offer store credit in exchange. Large chain stores like Petco and PetSmart have inconsistent policies that vary by location, so your experience will depend on the manager. Bring the fish in a sealed bag with its tank water, and be prepared for the possibility that the store says no.
Contact a Public Aquarium or School
Public aquariums, zoos with aquatic exhibits, science museums, and school biology departments sometimes accept donated fish, particularly larger or more exotic species that are educational to display. This is a long shot for common species like guppies or tetras, but if you have an arowana, a large cichlid, or a sizable pleco, it’s worth making a few calls. Some teachers also welcome classroom aquariums, though end-of-school-year releases are such a common problem that conservation groups like Habitattitude have developed educational materials specifically discouraging it.
How to Transport Fish Safely
Whether you’re driving fish to a new owner or shipping them, proper transport keeps them alive and healthy. For short car trips, place each fish in a sturdy plastic bag filled about one-third with tank water and two-thirds with air. Double-bag to prevent leaks, and set the bags inside an insulated cooler to stabilize temperature. Avoid feeding the fish for 24 hours beforehand, which reduces waste production during transit.
Temperature matters more than most people realize. A fish’s metabolic rate doubles with every 18°F increase in water temperature, which means warmer water burns through oxygen faster and produces more ammonia. For most tropical freshwater species, aim for a transport temperature around 55 to 60°F. You can add gel packs to the cooler to bring the temperature down gradually. Half a pound of ice lowers one gallon of water by about 10°F. For longer trips or shipping, insulated Styrofoam boxes inside cardboard shipping containers are standard. If you’re mailing fish, many hobbyists use breather bags or sealed bags filled with pure oxygen to keep dissolved oxygen levels high throughout transit.
Humane Euthanasia as a Last Resort
If you’ve exhausted every option and truly cannot rehome your fish, humane euthanasia is preferable to releasing it. The American Veterinary Medical Association recognizes clove oil (eugenol) as an acceptable method. You dissolve clove oil in warm water, then add it to a container holding the fish. Low concentrations sedate the fish first; euthanasia requires roughly ten times the anesthetic dose. The fish loses consciousness before dying, making this far more humane than the alternatives.
Two methods the AVMA specifically calls unacceptable: flushing fish into sewer or septic systems, and placing live, unanesthetized fish into a freezer. Freezing without prior sedation causes ice crystals to form in the fish’s tissues while it’s still conscious, which is painful and slow. If you’re unsure about the process, a veterinarian who treats exotic animals can perform euthanasia for you, typically for a small office visit fee.
Selling or Donating Your Equipment
If you’re leaving the hobby entirely, your tank, filter, heater, and accessories have value. Facebook Marketplace, Craigslist, and local aquarium club groups are the most common platforms for selling used gear. Used bare tanks in good condition typically sell for around a dollar per gallon, though large tanks (200 gallons and up) command higher prices. Bundling a complete setup, with the tank, stand, filter, heater, and lighting together, moves faster and appeals to beginners looking for an all-in-one deal.
Before selling or donating, clean everything thoroughly with white vinegar and rinse well. Never use soap or chemical cleaners on anything that will hold fish. If you had a disease outbreak in the tank, a diluted bleach solution (one part bleach to nineteen parts water) followed by thorough rinsing and dechlorination is the safest way to sanitize hard surfaces. Let everything air dry completely before packing it up.