A dead, round goby — an aggressive fish native to the Black Sea that has become a major problem in the Great Lakes — was recently found in the Susquehanna River near Binghamton, NY.

An angler discovered the fish floating in the river not far from the Pennsylvania state line and reported it to the New York Department of Environmental Conservation. Biologists who examined the fish concluded it most likely had been used as bait, as a hook had been run through its side.

As a result, David Lemon, the DEC’s regional fisheries manager, said biologists do not believe the fish came from a breeding population in the river, but they are concerned that whoever used the goby for bait may have released others.

No special sampling is planned to look for other gobies in the river because finding one would be “a needle in a haystack,” Lemon said, but he added that biologists would look for the exotic invader when they do routine sampling.

“If they do establish themselves, they are going to make their presence known in coming years,” Lemon said. “We do some sampling in the river each year.”

A breeding round goby population could have a significant impact on other species in the Susquehanna — including smallmouth bass which are already struggling in the river — and would have the potential to eventually reach the Chesapeake.

“It’s hard to overstate the impact of these gobies,” said James Grazio, a Great Lakes biologist with the Pennsylvania Department of Environmental Protection. “These are very successful invading fishes, and they have a proven track record of significant damage.”

Round gobies are native to Eurasia, where they originally lived in the Black, Caspian and Azov seas and their tributaries, consuming large numbers of zebra mussels. In 1990, they were discovered in the St. Clair River, which drains Lake Huron. Biologists believe the fish were inadvertently transported to the Great Lakes in the ballast water of ocean-going ships. They have also invaded other lake and river systems in Europe in recent decades.

Gobies are bottom feeders that eat benthic dwellers such as mollusks, clams, insects, snails, small fish and fish eggs. They are soft-bodied and can reach 10 inches in length, though adults in the Great Lakes typically are less than 7 inches. Young gobies are slate gray, while older fish are mottled with black and brown, and have a greenish dorsal fin with a black spot. Males may be entirely black when spawning. They have a large head with protruding eyes, like those of a frog.

They outcompete native fish in bottom habitats with their aggressive nature, chasing them from nesting sites and consuming their eggs. They are able to detect movement and consume food in complete darkness, unlike native species, and can tolerate poorer water quality. They have directly impacted populations of sculpins, logperch and darters, and biologist blame round gobies for hampering efforts to restore native lake trout populations.

They have a complex relationship with larger predators, such as smallmouth bass, yellow perch and walleye, Round gobies are an abundant, and popular, source of food for many game fish. But they also raid the egg nests of species such as smallmouth bass — a single round goby can eat 4,000 smallmouth bass eggs in 15 minutes. While smallmouth bass guard their nests, abundant round gobies are often ready to take advantage of any absence. “They can be very detrimental,” Grazio said. Ohio has had to periodically close its smallmouth bass fishery in Lake Erie as the result of low numbers of fish.

Even one of the good things they do can become a problem. Round gobies are major consumers of zebra mussels, one of their main food sources in their native Black Sea region. They can eat up to 78 a day. The mussels have also infested the Great Lakes, where in many areas the filter-feeding mussels build up toxins, which then accumulate in the gobies that eat them. These toxins are ultimately passed on to sports fish, creating a potential health problem for people who consume them.

Round gobies are also able to live in rivers, having already spread to the Mississippi basin. “I think the question is, does the Susquehanna have suitable, slow, deep water habitat for the goby?” Grazio said. “They don’t do well in swift currents.” Gobies don’t have swim bladders, so they have trouble passing obstacles to move upstream, he added, though they can move downstream past dams and other impediments.

If they made it to the Chesapeake, they are capable of tolerating low-salinity waters, like those found in the Black Sea.

“A lot of people consider the round goby to be a model of a perfect invading species because it has such a wide range of tolerances,” Grazio said. Once they establish, they can be highly productive — a female can produce six batches of eggs in a spawning season.

The Susquehanna borders the Great Lakes watershed in New York. “It is pretty concerning,” said Matthew Shank, a biologist with the Susquehanna River Basin Commission. “There is obviously something going on where it jumped from the Great Lakes inland to the Susquehanna.”

Three years ago, round gobies were discovered in a gravel pit near Erie, PA. Their presence was thought to have stemmed from a release of bait fish.

Although the transfer of round gobies as bait is prohibited, Grazio said it is not uncommon to see them in bait buckets. “They are small, they are excellent bait for a lot of bottom-dwelling fish like smallmouth bass, and people know that and they move them around,” he said. “There is a great likelihood of them being spread to other watersheds by bait buckets.”

Help prevent the spread of the round goby

Preventing the spread of round gobies to new areas is the best way to prevent further ecological and economic damage. Anglers are often the first to discover new infestations because they are commonly caught by hook and line. Here’s how to help:

  • Always check for and remove any plants, mud and debris from boats, trailers, clothing and equipment before leaving a water body.
  • Young goby can resemble bait fish, so it’s important to drain water from bait buckets, bilges and live wells before going to another area.
  • Clean and dry all equipment after fishing.
  • Never use round gobies as bait.

Pennsylvania Sea Grant