Logo Fragments Left
Logo Fragments Right
ISC Inner Banner
ISC - Banner

Learn About Invasive Species

HOMEbreadcrumb separatorLEARNbreadcrumb separatorInvasive Fish and Invertebrates

Invasive Fish and Invertebrates 


Invasive aquatic species pose a significant threat to all water bodies from small streams to the Great Lakes. Most invasive aquatic species dramatically alter food web structures, decreasing the food available for native species. This direct competition leads to population decline and loss of biodiversity. The loss of native fish species also dramatically impacts the fishing industry, both commercial and recreational. Invasive aquatic species pose a serious threat to the use of water bodies, making it difficult and even dangerous to swim and boat. Human activity is a primary reason why invasive aquatic species spread; improper equipment cleaning and illegal transportation of fish has made it possible for the invasion of isolated water systems. All water sport equipment, clothing, and pets must be cleaned thoroughly after they come out of the water. Also, it is illegal to transport invasive fish between water bodies and to possess live invasive aquatic species.


Asian Carp

Asian carp refers to four species, bighead, black, grass, and silver carp. Asian carp are native to China and southern Russia but were brought into the U.S. as a biocontrol method in aquaculture; they escaped into the wild and have become established in the eastern United States. Asian carp thrive in cool water temperatures, reproduce rapidly, eat up to 20% of their body weight in plankton a day, and displace native species competing for food and space. Also, when they feel vibrations through the water, carp will leap up to 3 metres into the air which can cause serious injury to boaters and other water users. It is illegal to have live Asian carp in your possession in Canada; any information regarding importing or distribution and any potential sightings of this invasive aquatic species should be reported immediately. Also, bait must only be used from the area you are going to fish and must not be transported. For in-depth information regarding Asian carp and what is being done to keep them out of the Great Lakes go to Asian Carp Canada at asiancarp.ca.

Fact Sheet

Sea Lamprey

Sea lampreys are eel like fish that cylindrical and can be 30 to 80 centimetres long. They have dark grey or brown leathery skin with dark markings and a light underbelly. They have two thin dorsal fins and seven distinct gill holes on each side. Their mouth is a large sucker with rings of sharp teeth and a raspy tongue, used to latch onto the side of fish and feed on its blood. If the fish survives the lamprey attack it will be left with a large open wound that normally becomes infected, causing the fish to die. This invasive aquatic species has reduced the number of sport fish in the Great Lakes as only 1/7 of fish attacked survive. If a fish is caught with a sea lamprey attached, the lamprey should be killed and put in the garbage. Never return a sea lamprey to the water, and contact the Sea Lamprey Control Centre of Fisheries and Oceans Canada at 1-800-553-9091 regarding any sea lamprey questions.

Fact Sheet

Rusty Crayfish

Rusty crayfish are large and aggressive, with adults reaching a body length of 7.5 to 13 centimetres (not including claws). This invasive aquatic species gets its name from the rust coloured patches that run down either side; the rest of the body is gray/green to red/brown. While the rusty crayfish look similar to native crayfish they are distinguishable by the oval space between their closed claws, and their pinched concave rostrum. Because of their size and aggressive feeding nature, they out-compete native species for food and space. They also damage fish populations by consuming aquatic vegetation needed for fish to spawn in and raise young. It is illegal to transport any crayfish species, dead or alive, and they can only be used for bait in the water in which they were caught.

Fact Sheet

Zebra and Quagga Mussels

Zebra and Quagga mussels are invasive freshwater mussels that are throughout the Great Lakes. They are, on average, around two centimeters and do not sit flat. They are light with dark brown markings; zebra mussels have a zigzag pattern and quagga mussels have dark concentric rings. Mussels filter plankton out of the water, which depletes it as a food source for native species. Large colonies can take over fish spawning areas and beaches, cutting the feet of potential swimmers. They also clog water intake lines because of their dense colonies. These invasive mussels also increase the presence of toxic algal blooms which can have health impacts on native wildlife. Zebra and Quagga mussels latch on to boats and are easily passed from water to water; ensure that all plants, animals, and mud is removed from boats and trailers before leaving an area.

Round Goby

The round goby is a small, bottom dwelling fish that aggressively feeds on small aquatic organisms and can spawn several times each year. Adult round goby can be between 6 and 16 centimeters long with a cylindrical body and rounded snout. They are fully scaled and are mostly brown or olive with dark brown and black spots. Round goby decrease the levels of native fish by eating eggs and young and by out competing them for food. It is also suggested that round goby pass a strain of botulism to the birds and fish that eat them; this toxin comes from the zebra mussels that the goby eat and causes fish and bird death. It is illegal in Canada to possess live round goby or use them as bait. Never transport fish from lake to lake and make sure to always wash your equipment after being in the water.

Fact Sheet

Northern Snakehead

The northern snakehead is a predatory fish that can live in a wide variety of water conditions; they have the ability to “walk” short distances on land and its lung-like organ allows them to survive out of water for up to four days. Northern snakeheads can reach up to 85 cm and have a dark and light brown mottled, thin elongated body. They have a large mouth filled with teeth and a single long dorsal fin. This fish can consume a wide variety of food including fish, amphibians, insects, invertebrates, small reptiles, birds and mammals. Although not in the Great Lakes yet, the northern snakehead is capable of adapting to Ontario waters easily. It is against the law to have a live snakehead in your possession. Do not transport and release live fish into any waterbody.

Fact Sheet

Killer Shrimp

Killer shrimp are an aggressive predatory freshwater invasive invertebrate. They grow up to three centimetres long, have two tail cones, and two large powerful mandibles. Killer shrimp can either be solid in colour or have a striped pattern. It is so named because of its aggressive feeding habits, the killer shrimp consumes large amounts of aquatic insect larva and food that native fish rely on. They also kill large amounts of organisms but don’t actually consume them. This feeding behaviour disrupts food webs and decreases native biodiversity. Killer shrimp can survive up to four days outside of water making it very easy to accidentally transfer them from water body to water body. It is very important that all fishing equipment is properly cleaned between uses and that your boat is washed off before switching water bodies.

Fact Sheet