There are many different types of gobies and they have a worldwide distribution in salt and freshwater systems. These benthic fish species have the potential to seriously impact North American aquatic ecosystems in the future. The round goby, Neogobius melanostomus and the tubenose goby, Proterorhinus marmoratus, are bottom dwelling freshwater fish native to Eurasia and are considered invasive species which were accidently introduced into the habitats/ecosystem here in the United States. The species are originally native to the Caspian and Black Sea regions including their tributaries and the adjacent waters in Europe and Asia, where they are actually fished commercially and used as bait fish since they are already indigenous to the area. As transatlantic ships have come from these areas into the Great Lakes, the gobies have been transported and accidently released into the Great Lakes from the ballast water discharged by the ships. The round and tubenose goby were first reported as seen in Lake St. Clair in 1990. Both types of gobies have since spread into each of the Great Lakes and are working their way inland through the rivers, such as the Mississippi River system, and canal systems, where they continue to be an invasive species. The tubenose goby is actually considered an endangered species in its native habitat and continues to remain uncommon in the United States waters, quite possibly because, even though they are both invasive species, the tubenose goby is not as aggressive towards other native fish as the round goby.
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The distinguishing characteristics between the tubenose and the round goby are the black spot on the dorsal fin, thick lips and the frog like eyes, which seem to be specific characteristics the round goby has. It may be hard to tell the difference between the native species (sculpins) to the invasive species (round gobies), but the goby's have a fused pelvic fin unlike any native species that might look similar to them. The fused fins act as a suction cup which allows the goby to attach themselves to the bottom of the substrate.
The morphology of the juvenile and adult round gobies are about the same, except for the color. Both juvenile and adult gobies have the black spot on the front dorsal fin, except the juvenile has more of a light border around the black spot. The juvenile color is slate gray solid in color and the adults are made up more of different colors such as mottled gray, olive green, and brown markings.
The life cycle of a goby starts out with the eggs which are about 4 x 2.2 mm in size. The female hits maturity between 1-2 years and the males hit maturity between 3-4 years and the male actually ends up dying right after they spawn. Spawning happens April through September and the female can spawn up to 6 times every 20 days during each spawning season. The female lays between 300-5000 eggs each year. The males guard the nests and attract females to spawn in the particular nest which may have eggs from many different females in it.
Generally, gobies are larger than most species they compete with, they also have a well developed sensory system, which helps them to easily detect water movement, allowing them to be able to feed in total darkness using their highly sensitive lateral line to detect prey. Gobies are also known to be aggressive feeders eating young fry, eggs, and smaller fish but they are also aggressive defenders of their territory which ends up displacing native fish from their own habitat. Round gobies are robust and can also tolerate a wide range of environmental conditions (temperature, oxygen, salinity, and water quality). Gobies are able to survive in eurythermal temperatures, but tend to thrive in warmer water. Thirteen percent of the gobies respiration is obtained via the skin, which makes them also able to withstand low oxygen concentrations. They can inhabit slightly brackish waters or fresh water and inhabit water depths from zero to thirty meters. They also are able to survive under degraded water conditions, which make them such a great invasive species. These are some of the factors that give the gobies a competitive advantage over native species, such as sculpins and logperch, which have been affected by the goby invasion.
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Gobies are found in rivers and near the shore of lakes, preferring rocky habitats with many opportunities to hide. They are mostly found in habitats that are rocky, cobble, and gravel surroundings but can be found in fine gravel and sandy substrates in which they may burrow to hide from possible predators within the area.
Studies within the United States have revealed the diet of gobies includes insect larvae and zebra mussels. Other organisms which gobies prey on are benthic organisms such as mollusks, crustaceans, worms, fish eggs, small fish and insect larvae. In their native habitat, the diet of gobies consists of similar types of fish and organisms as those in the U.S. This is why the gobies have been able to adapt so well to the different habitats within the Great Lakes; the Great Lakes environment and their native environment have similar prey for them to feed on. The gobies main diet is made up of approximately seventy zebra mussels a day, another invasive species, which happens to filter the toxins out of their habitat, in this case the Great Lakes. When the gobies eat the zebra mussels, they accumulate these toxins in their system, then the contaminants are passed on to the larger sport fish such as smallmouth, rock bass, walleyes, yellow perch, and brown trout if they feed on the gobies. This chain of passing toxins along has increased some health concerns about eating these sport fish.
The gobies have positive and negative impacts on the waterways and lakes in the U.S. The positive impacts of gobies are that they eat many zebra mussels each day, which are another invasive species, they also serve as food for larger predatory fishes because larger fish still need to be able to eat, and are easily caught by anglers and provide some sport because the round goby is aggressive and will attack the bait on the hook.
The negative impact of the gobies is due to their competitive nature. They compete successfully with native bottom dwelling fish, such as sculpins and darters, and drive them from their habitats. In the U.S., they end up out-competing the native fish for food resources, such as eggs, fry, and smaller fish, due to their unique ability to feed in darkness. Interestingly, it has been found that gobies, in their native habitat, do not negatively affect populations of other species. This might be because they have come to a balance in their native environment and are now co-existing with other species. The adult male gobies will aggressively defend spawning sites and may occupy the prime spawning areas in the native fish's habitat, keeping natives out. Another negative impact is they aggressively take bait from anglers hooks, where they end up getting caught on the hook instead.
Scientists claim they will be unlikely to remove the gobies from the Great Lakes because of their aggressiveness. Since the gobies will be unable to be fully removed from the Great Lakes, control measures are being taken in order to help prevent the spread of the fish. Electrical nets are being used to deter the gobies movement into inland streams, rivers and lakes. Piscicides, chemical substances which are poisonous to fish and used to eliminate a dominant species of fish in a body of water, are being used to deter the movement of invasive fish species, such as the goby. Regulations are also being put into place to prohibit the capture or possession and transport of gobies as bait fish. These are ways that management efforts are trying to control them, but there is actually little information on successful management options for this species.
In order to help avoid the spread of the gobies any further into the waterways in the U.S, the Wisconsin DNR asks anglers to: not use round gobies as bait, to dump the bait buckets on land, to help stop spread of all aquatic exotics by cleaning your boat and trailer before going to a new water body because this is how the gobies were initially transferred, to drain the water from your boat motor and wells on land, and to remove plants and debris from your trailer before leaving the launch ramp. Following these simple steps every time you leave the water or every time you enter the water, will help the DNR keep the goby, and other invasive species, under control.
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Gobies, an invasive species originating in Eurasia, and now found in the Great Lakes, are an aggressive fish. Scientists who have done studies claim they will be unlikely to remove the gobies from the Great Lakes partly due to the large number of eggs that are produced, their well developed sensory system, and their ability to survive in a variety of water conditions, including degraded water quality conditions. Even though they may never be fully removed from the Great Lakes, attempts are being made to prevent further spread into additional U.S. waterways via electrical barriers, chemicals and regulations.
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