What it takes to be a successful Invader

Invasive species have received a lot of bad press, but let’s face it, some of these alien species really have what it takes to make it!  One example of a highly successful invasive species is the Round Goby, a native to central Eurasia including the Black Sea and the Caspian Sea.

Male Round Goby in black spawning coloration

Male Round Goby in black spawning coloration

Identifying an alien

Recently a graduate student in Michigan sent a request for identification of a fish skull.  When I saw the skull on a photo that the student attached to the inquiry my first thought was that this is a species I haven’t seen before.  I was thinking to myself, “in my mind I’ve got a fairly good catalog of all the native species that are found in the Great Lakes, so this one is probably exotic”.  Furthermore, I examined the teeth and the rest of the skull picture, and found features that are similar to the marine blennies and gobies that I’m familiar with; quite possibly a Round Goby.

OSUM 104701, Neogobius melanostomus skull

OSUM 104701, Neogobius melanostomus skull

When one observes the teeth of a Round Goby skull, it becomes readily apparent that they are eminently suited to catching prey: numerous, closely packed and somewhat curved teeth. Once the fangs are sunk into the prey’s body it would be difficult to wriggle out of the goby’s maw.  Speaking of the “maw”, the width of the Round Goby’s head and mouth are somewhat disproportionately large in comparison to the size of the body.  This aspect of the anatomy amplifies the capacity of the fish to suck in its prey.  By opening the mouth quickly a vacuum is created, which when combined with the sudden forward lunge that the goby employs toward the prey, improves the likelihood of successful capture.

Neogobius melanostomus are extremely aggressive and will challenge fishes larger than themselves, outcompeting native fish for preferred habitat as well as preying on other fish’s eggs and young.

What makes the Round Goby so successful?

Round Gobies are found primarily in the benthic zone of the water body, from the bottom of shallow areas down to 70 feet in depth.  They prefer areas where there is plenty of cover such as around rocks, sticks and logs.  The species has been found to tolerate polluted conditions, which enables it to occupy areas that less tolerant species cannot live in. This increases their opportunities to grow into a large population that aids in overcoming the other species in less polluted areas.  Another aspect of their biology that enhances their prowess is a highly developed lateralis system, a fishes’ sensory system conveying environmental information to the brain and making them an effective competitor and predator in dark, murky conditions as well as in clear daylight.

High productivity is a hallmark of an effective invader.  A mature Round Goby female is able to produce over 3,000 eggs, the older the female the more eggs they produce.  The male uses posturing and coloration (see the photo above) to attract females to its nest, often mating with more than one female.  The females spawn up to six times in a season, which lasts all summer long from April through September. Let’s do the math: a female could produce 18,000 young in just one year, that’s a lot of Round Gobies!

Although the deleterious effects of this intruder are considerable in scope, as some research here at OSU has shown, one must nonetheless admire their capabilities.  But we should keep in mind that without our assistance it is doubtful that Round Gobies would have spread so far and certainly not so quickly.  Their ability to tolerate euryhaline conditions, a wide range of salinities, facilitates their natural spread under normal conditions over a much longer time. It has allowed them to survive in the ballast waters of vessels and occupy new areas when the ballast is flushed.

Although they are best known from the Great Lakes they are now found in the lower reaches of larger rivers and have been captured in the Illinois River drainage, presaging their invasion of other Mississippi River tributaries.

map of Round Goby invasion in Great lakes regionBut thus far the most dramatic spread of the Round Goby has occurred in the Great Lakes of North America where a lack of effective competitors facilitated their occupation of new territories.

Northern Europe, too, has suffered from a Round Goby Invasion as shown in these maps and the potential for their spread in Europe is estimated to be much greater. You can follow them on AquaMaps, enter genus “Neogobius” and species “melanostomus” to obtain a map showing their predicted spread.

map of Round Goby invasion in Europe

 

Because they are not tasty to humans it is hard to truly appreciate this fish from any perspective other than that of their successes as invaders. But to a larger, piscine predator they must indeed be tasty as they have become a substantial part of native gamefishes’ diet.  And for Lake Erie water snakes, as well as aquatic birds like gulls and cormorants, Round Gobies are a major new item on the menu.  Indeed, Round Gobies are so abundant in Lake Erie that frustrated anglers often complain that the pesky little perciforms are the only thing they can catch.

The Round Goby is here to stay, and changes wrought by their incursion will reverberate for decades across the Great Lakes at least. Have you caught one yet?

 

About the Author: Marc Kibbey is Associate Curator of the Fish Division at the Museum of Biological Diversity.

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