The aquarium trade is a popular business and it is not difficult to obtain a pet fish. People may purchase fish for a hobby and others may have gained an additional pet goldfish when their child won at a ring toss game at the county fair. For as many reasons people get a pet fish there are just as many reasons for why they may eventually want to it up. The fish may be sick, noncompatible with other tankmates, it may be too expensive to upgrade the aquarium when the fish grows, moving to a new apartment is a hassle with an aquarium and the list goes on. The issue with this choice is when a fish owner decides that the most humane way to treat their pet is to release it to swim free in the wild (1).
Unfortunately releasing a pet is unethical due to the physiological stress from the new environment, it’s susceptibility to parasites and disease and possible predation from a larger predator (1). If the pet(s) survive then there is a risk of the fish establishing a population and spreading which can be ecologically harmful if the fish is in a nonnative habitat. In the United states alone, 75 if 185 different exotic fishes that have been caught are known to have established breeding populations, with half of them being due to release or escape (1).
When a pet exotic fish becomes invasive it is not only costly to remove but can harm native species and alter predator prey dynamics. A classic example of the pet trade influencing invasive species is with the goldfish (Carassius auratus). The goldfish is a durable fish, that can tolerate a wide range of conditions, which makes all continents except Antarctica carry potential habitats for the fish (2). When the fish is established, the fish may deplete native food resources, taking away from native organisms. The fish can decrease the overall diversity of an ecosystem by uprooting plants and predation, increase cyanobacterial blooms, and alter the chemical properties of the water (2,3).
A solution to preventing invasive establishment is to return unwanted fish to a local pet store for resale or trade. The fish may also be given to another hobbyist, public aquarium or even a public institution such as a school. The last option is to have a fish humanely euthanized and assistance can be sought by a veterinarian or fishery biologist (1).
References
1) Problems with the Release of Exotic Fish. USGS. Available at https://nas.er.usgs.gov/taxgroup/fish/docs/dont_rel.aspx (Last accessed November 1, 2017).
2) Pinto L, Chandrasena N, Pera J, et al (2005) Managing invasive carp (Cyprinus carpio L.) for habitat enhancement at Botany Wetlands, Australia. Aquatic Conservation: Marine and Freshwater Ecosystems 15:447-462.
3) Guo Z, Sheath D, Trigo FA, et al (2016) Comparative functional responses of native and high-impacting invasive fishes: impact predictions for native prey populations. Ecology of Freshwater Fish 26:533-540.
