The round goby is a well-studied invasive species introduced to the United States from Europe and Asia in ship ballast water from the Black Sea. This is the same method by which zebra mussels (Dreissena polymorpha), another invasive species and the round goby’s preferred prey species, were introduced to the Great Lakes.
Round gobies are small, brown fish with elongated bodies that average between 4 and 10 inches (10 and 25.4 cm) in length. In North America, the round goby competes with other generalist predators, especially the mottled sculpin (Cottus bairdii), for food and breeding territory. Unfortunately, the two species are also difficult to distinguish, making management efforts difficult. Other species impacted by the round goby include the northern madtom (Noturus stigmosus) and the sand darter (Ammocrypta pellucida).
In their native range, round gobies are essential members of their local food chain. Generally, gobies are abundant and a critical food source for many piscivorous birds, fish, and other animals. In addition, round gobies eat many invertebrates and are an intermediate link in the food chain between insects and top predators. They are also highly tolerant of adverse water conditions and thrive in many different habitats, ensuring they can survive when other, more sensitive species may not fare well. Unfortunately, round gobies are also a nuisance to anglers because they steal bait from anglers’ hooks.
What Are Gobies?
Gobies are fish that belong to the suborder Gobioidei in the order Perciformes, which contains over 2,200 different goby species. They occupy many different habitat types, including fresh, brackish, and saltwater habitats. Additionally, round gobies specialize in environments other fish cannot access and are highly adaptable to adverse conditions (i.e. drought, pollution, salinity). Typically, gobies are found at the bottom of the water column and use their large, round pectoral fins to perch on submerged debris. However, their small size enables them to fit into tight spaces, and therefore many goby species have evolved to construct small burrows in the substrate where they hide or nest.
This group of fish has evolved to suit various niches, from scavengers that pick parasites off of marine animals to semi-terrestrial mudskippers (subfamily Oxudercinae) that can take regular walks on land. Some gobies even form mutualistic relationships with pistol shrimp, where the shrimp digs and defends a burrow, and the goby, with its superior eyesight, alerts the shrimp to danger. Not all gobies are invasive; many have unique and exciting survival strategies.
Why Is the Round Goby Invasive in North America?
In North America, the round goby is considered non-native, meaning that it was introduced from another ecosystem, and it is invasive, meaning that it harms introduced ecosystems. Established populations are present in the Great Lakes and connected waterways. Species within this region evolved to occupy specific niches, ensuring a balance within the ecosystem. When a dietary generalist, like the round goby, is introduced, it directly competes with any native generalists, and it often thrives in an introduced environment because native predators did not evolve to hunt the introduced species. Round gobies are also aggressive towards other fish and viciously chase away other species from hunting grounds.
Round gobies unintentionally work with the zebra mussel to destabilize ecosystems in the Great Lakes. The zebra mussels thrive in the Great Lakes, where there are fewer predators to eat them and plenty of structures and substrates for zebra mussels to build colonies on, often clogging pipes and causing millions of dollars in property damage. They also feed on algae that other native mussels would typically feed on. Round gobies have a similar effect on native environments but thrive where zebra mussels are present because round gobies eat them. The introduction of both species in the Great Lakes has exacerbated their adverse effects on this ecosystem in an “invasional meltdown” where two invasive species “help” each other establish in or damage their introduced environment.
In addition to competition, the zebra mussel and round goby increase the frequency of disease in the Great Lakes. For example, avian botulism is passed from zebra mussels to gobies and then to piscivorous birds that eat the gobies. Gobies are also a host for viral hemorrhagic septicemia, a virus that infects fish.
How Can I Tell the Difference Between Mottled Sculpin & Round Goby?
Round gobies are easily distinguished from other species of North American fish based on their pectoral fins. Gobies have fused pelvic fins that form a suction cup, allowing them to perch on rocks. They also have prominent cheeks and eyes positioned at the top of their head.
Round gobies are mottled in color and most closely resemble mottled sculpins, although sculpins lack the fused pelvic fins found in gobies. Round gobies also have a distinctive black spot on their first dorsal fin. Both species have large, rounded pectoral fins, but mottled sculpins have more distinct recessed webbing in between the spines that give the fin its structure.
Where Do Round Gobies Live?
Round gobies are found at the bottom of the water column in nearshore areas of lakes and rivers near aquatic plants. They use their fused pectoral fin to stick to the surface of rocks and other debris and will quickly dart from a perching position back into submerged vegetation if they spot a predator. From their perches, round gobies will readily consume any mollusks or aquatic insects and scavenge for fish eggs.
They can tolerate a wide range of temperatures from 32 to 86 °F (0 to 30 °C). Additionally, they are tolerant of salinity and are able to survive in water with a salinity of up to 3.5%. Low dissolved oxygen and high turbidity are also not a problem for the round goby. This impressive environmental tolerance is one reason why they are such successful invaders in the Great Lakes.
Round Goby Reproduction Facts
Adult round gobies can reproduce at 2 to 3 years of age. During the mating season, which extends from April to September, the male round goby will find a suitable nesting site where they prepare a suitable space for female round gobies to lay their eggs. Males also change colors to attract a mate and don a dark coloration during the breeding season. Female gobies will visit nests and lay adhesive eggs on a solid structure like a rock, shells, or nearby plants. The male will guard their eggs until they hatch and are known to die at the end of the spawning season.
