Small Fish, Big Effect: Invasive Round Goby

Help Stop the Spread

Anglers, we need your help! While fishing, have you caught this small bottom-dwelling fish? Credit Valley Conservation (CVC) has received reports of round goby (Neogobius melanostomus), an invasive fish species, spotted in two new locations in the Credit River Watershed.

Round goby is confirmed by CVC to be present in Fairy Lake in Acton. Their presence in the pond at Ken Whillans Conservation Area has also been reported but is still unconfirmed by CVC. Previous confirmed sightings of round goby in the watershed are in the West Credit River in Hillsburgh and the lower Credit River near Port Credit.

Help stop the spread with our identification tips, history and reporting tools.

Identifying Round Goby

A small brown and olive-coloured fish with dark brown and black spots, inside a clear plastic container of water. — Round gobies are fully scaled and mostly brown or olive with dark brown and black spots.

Before you can help stop the spread, you need to know how to identify round goby. These fish can be mistaken for other native fish.

You can identify round goby by looking for two key features:

A large black spot on their dorsal, or back fin.

A person holding a pebble and a small brown and olive-coloured fish with dark brown and black spots. — Round goby can be between six and sixteen centimetres long with a cylindrical body and a rounded snout. They can be identified by the prominent black spot on their dorsal fin.

A fused pelvic, or bottom fins.

A person holding a small fish showing the under belly and its fused bottom fins. — You can identify round goby by their fused pelvic fin.

How Did Round Gobies Get Here?

Round goby is a native fish of the Black and Caspian Seas. It made its way to North America through the ballast waters of ships. Ballast water is held in the ballast tanks of ships and is used to provide stability and maneuverability during a voyage. Ballast water is one of the major pathways for introducing non-native aquatic species into new environments.

Researchers first discovered round goby in the St. Clair River in 1990. Within five years, round goby became established in all five Great Lakes.

Understanding Their Expansion

We saw the rapid expansion of round goby because of their ability to out compete native species and prolific spawning.

Round goby compete with our native species for habitat and food. Native fish populations are threatened in areas where round gobies are present because of their consumption of native fish eggs.

Another key component of the round goby diet is mussels, such as the invasive zebra mussel (Dreissena polymorpha). Zebra mussels invaded the Great Lakes just a few years before round gobies arrived. This provided an abundant food source contributing to their spread.

Round goby spawn multiple times from late spring to early fall. Male round gobies take care of their clutch, which contain hundreds to thousands of eggs. They fan eggs to keep them oxygenated and protect them from predators. This can result in a successful hatch rate of up to 95 per cent.

Present Status

A top-down view of a small dark brown and green fish in a plastic container filled with water. — Young round gobies are solid slate grey. Older fish are blotched with black and brown and have a white to greenish dorsal fin with a black spot at the back fin.

The spread of round goby into inland lakes and ponds has been continuous since they became established in the Great Lakes. The illegal use of round goby as baitfish often leads to their invasion into inland lakes and ponds. The provincial government has banned the possession and use of round goby as bait. Even with the ban in place, we need help from anglers like you to stop the spread.

Catch and Report

Using your seasoned angler knowledge and our helpful identification tips, report your catches of round goby.

Use our online invasive species reporting tool and EDDMapS. Make sure to include the location and a photo. Round gobies should be destroyed. Do not release them back into any waters.

You can take more steps to stop the spread of invasive species by keeping your boat clean. Follow the steps outlined in the Clean, Drain, Dry program.

Learn how CVC is managing and removing invasive species to protect our watershed’s natural biodiversity and beauty.

By Claire Doherty, Assistant, Natural Heritage Management