It’s the very definition of big fish in a small pond — in this case, a whole lot of supersized goldfish in a Toronto-area stormwater pond.
Last summer, biologists were surprised (and more than a little concerned) to discover some 20,000 goldfish in a pond the size of a couple of basketball courts. Likely flushed down the toilet, the tiny pets were obviously thriving. Not only are they breeding, but some have become massive three-pound versions of the ubiquitous fish in a bowl.
Given that stormwater ponds are incredibly dirty and polluted, ecologists are the University of Toronto and Fisheries and Oceans Canada are concerned that the extra-large, extra-tolerant fish may become “superinvaders” that will outcompete native species as they invariably spread and make their way into the Great Lakes ecosystem.
The story, reported in Scientific American, noted that Asian carp are already present in the Great Lakes, but that these urban pond fish could wreak even more havoc as they have adapted to a low-oxygen, warm-water environment.
Future management comes down to prevention. Fish owners need to know how important it is to return unwanted pets to the store or give them to a friend instead of dumping them. And land developers and engineers may need to design stormwater ponds, perhaps building barriers between ponds and adjacent waterways or stocking them with goldfish predators such as native largemouth bass.