Once the pet goldfish familiar to many people is released into ponds, lakes or other natural freshwater environments, it may trigger a chain of ecological damage, with an impact far beyond public imagination.A research team from the University of Toledo and the University of Missouri said they have obtained the strongest evidence to date through controlled experiments that goldfish will significantly disrupt freshwater ecosystems after entering the wild; the relevant research results have been published in the Journal of Animal Ecology.
Study leader William Hintz, associate professor in the Department of Environmental Science and Lake Erie Center at the University of Toledo, pointed out that the public must be aware that pets can become "pest species" under certain circumstances and cause harm to freshwater ecosystems. He said releasing goldfish into the wild may appear to some to be a well-intentioned act, but the practice could actually turn into a serious ecological threat.
In order to more accurately assess the ecological impact of goldfish, researchers conducted large-scale, controlled outdoor mesoscale ecological experiments to simulate operating conditions in a real lake environment. In the experiment, the research team introduced goldfish into two common types of simulated freshwater systems: one is an oligotrophic water body with a lower nutrient level, and the other is a eutrophic water body with a higher nutrient level, and continued to track system changes.
The results showed that after goldfish entered the system, the quality of the water environment deteriorated rapidly. Under eutrophic conditions, researchers observed a significant decrease in water clarity and a significant increase in suspended particles, indicating that the ecological balance has shifted significantly.
At the same time, native organisms declined at multiple trophic levels. The study pointed out that through direct feeding and disturbance of the habitat, goldfish have led to a significant reduction in basic organisms of the aquatic food web such as snails, amphipods and zooplankton. These small organisms are originally an important part of maintaining healthy freshwater ecosystems.
The study also found that native fish species were also negatively affected. Goldfish compete with native fish for food and other resources, reducing native fish's body condition, which is often seen as an important signal in assessing the long-term health of a population.
It is worth noting that neither oligotrophic nor eutrophic lakes are immune to the impact of goldfish. While the specific impacts on different types of water bodies vary, the researchers point out that no freshwater ecosystem can currently be considered "naturally immune" to goldfish invasion.
In terms of experimental design, the research team used both incremental and substitution methods to distinguish the impact of the goldfish itself from the impact of changes in the total number of fish. The results showed that although some changes in aquatic plant communities were related to overall fish density, the most severe ecological disturbances were caused directly by goldfish.
Researchers have also documented a phenomenon known as "state transition," in which ecosystems cross a certain tipping point and rapidly reorganize into a new, often more degraded state. Once this transition occurs, subsequent recovery is often difficult and costly.
The research team pointed out that in the context of the rapid expansion of the global pet trade, species are flowing across regions at an unprecedented rate, and goldfish is one of the most widely distributed ornamental fish in the world. Once they enter rivers, lakes and ponds due to artificial release or flooding, they may quickly establish invasive populations.
Rick Relyea, a professor in the College of Agriculture, Food and Natural Resources at the University of Missouri, director of the Johnny Morris Institute of Fisheries, Wetlands and Aquatic Systems, and co-author of the paper, said that goldfish will quickly grow into large individuals after being released into the wild. These fish will stir up lake bottom sediments, hunt large quantities of prey, and compete with native fish. Together, these behaviors amplify their damaging effects on ecosystem structure and function.
Based on the research results, scientists called on the natural resources management department to list goldfish as an invasive species that requires priority prevention and control, and to take prevention, monitoring and control measures as soon as possible. At the same time, the research team also emphasized that public education should be strengthened so that owners can fully understand the environmental risks that may arise from releasing aquatic pets at will.
For people who can no longer keep their goldfish, the researchers recommend alternative options, including returning the fish to a pet store, passing it on to another aquarist, or contacting local wildlife management agencies for advice.