A wetland 'goldfish bowl'. This is no fish story. Well, actually, it is...

Updated: Sep 4, 2019

By Patricia Lowe, Watershed Stewardship and Outreach Education,

Central Lake Ontario Conservation


Students Catherine and Allysa are part of CLOCA’s Aquatic Monitoring Crew who collect data in local wetlands, creeks and Lake Ontario, to help us better understand overall watershed health. One of their recent tasks was identifying fish communities in local wetlands along the north shore of Lake Ontario in our watershed; they use a boat and electrofishing equipment to shock the water, which stuns the fish long enough so they can easily be netted. The nets full of fish are brought onto the boat for processing and information about the species, size and capture location are recorded as data, to assess overall fish community health. The fish are then released back into the water, unharmed.


Ideally, we want to see a diverse population of native fish species in our wetlands when we do our monitoring. Imagine our students' surprise when electrofishing in Pumphouse Marsh recently, a Provincially Significant Wetland in Oshawa, when their fish capture was just domestic goldfish. Actually, hundreds of them. Yes, you got that right; those orange and gold pet fish found in backyard ponds or in a child’s fish bowl.


While those domestic environments are completely okay for goldfish, it’s what happens when garden ponds become overpopulated or the child loses interest in their nurturing of that pet that we at CLOCA encounter problems. From many years of monitoring water bodies in our watershed, those cute little fish end up in our lakes, ponds and wetlands.

Most people think that its perfectly fine to release goldfish into natural water bodies because they do in fact survive the winter and breed successfully. Well, Catherine and Allysa will tell you from their school studies and field experience that goldfish populations in Ontario’s ecosystem will significantly reduce overall biodiversity of native fish species in these systems.


Goldfish eat snails, small insects, fish eggs and young fish, making this fish a competitor with and a predator of our native fish populations. Because they are a member of the carp family, they also stir up mud and other matter in the bottom sediments of a water body when they feed. This further contributes to cloudiness in the water and impacts the growth of aquatic vegetation. In some situations, like in Pumphouse Marsh, they have the potential to produce a large population, unchecked with limited predators and very successful rates of reproduction, and we lose the diversity that is critical to watershed health. They can also carry domestic fish disease which can harm the native fish population.


We know in the case of Pumphouse Marsh that some of the goldfish have been in the pond for some time, and others have recently been delivered from folks in the surrounding community. The colour of the individual fish gives us a clue as to the length of time in their new home. If they are orange, they have recently been released. If they are gray and silver, they have been there for a couple of years. Over time they lose their gold colour, which is simply a mutation that made them attractive for domestic breeding in the first place.


So now you see the dilemma faced by Catherine and Allysa when they capture hundreds of goldfish. They cannot return them in good conscience because of the impact they will continue to have on that wetland’s ecosystem. So they made a few phone calls to nurseries in the pond business and pet stores to see if anyone could take their capture. You will be glad to know the fish have found a new home at Big Al’s Pet Store, where they will live out their goldfish years domestically, as they were intended to live.


If you've got a goldfish or two you don’t want, please don’t release them or any other aquatic pet or plant into our lakes, rivers or streams. Donate them to a pet store or local school. Both the fish and the recipient will be grateful.


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