What the Fish? Episode 9: Carpe Carpam

Seize the Carp

Ever been swimming at your favorite local spot and encounter a piranha? Believe it or not, this happens across North America all the time - not just in late night B-movies! So how does a fish that is native to South American freshwater rivers find itself living in a Missouri pond? Often these invasive species (a term that describes biodiversity that is introduced into a non-native environment and locale) are simply dropped off by pet-owners that are releasing them into the wild.  In some cases invasive species take hold in a non-native environment purely through accidental circumstances. Occasionally, invasive species are purposefully placed in a locality because someone thought they would serve a specific positive purpose. For example, mosquitofishes (Gambusia affinis) have been frequently introduced in non-native habitats because people wanted them to control mosquito populations. Join us and our special guest, Caleb McMahan, as we discuss this environmentally important topic.

Introducing non-native species frequently has negative effects for the local environment and biodiversity. Invasive species can dramatically alter the fragile ecosystems they are introduced into and severely threaten native wildlife. One example of an introduced fish that has reeked havoc on the native fishes of Illinois is the Round Goby (Neogobius melanostomus). The Round Goby was introduced into the Great Lakes (including Michigan) through freighter vessels traveling from the Black Sea. Once the Round Goby was accidentally brought to the lakes they began spreading at a rapid pace. Unfortunately, the increase in these invasive gobies has harmed many native fish populations, such as the Mottled Sculpin (Cottus bairdi). Round Gobies are voracious predators on the eggs and fry of other fishes and they are fiercely territorial with their spawning sites.  This creates competition with native fishes for reproductive space. Another invasive species in Illinois is the Grass Carp from Asia (Ctenopharyngodon idella), which was purposefully introduced in the United States in an effort to control aquatic weeds. The introduction of the grass carps into non-native habitats was carefully controlled, and many of the  introduced populations were gentically modified to be sterile in an effort to curb unwanted population growth in the wild. Despite these precautions, populations of Grass Carp have spread across the United States since their intial introduction in the 1960's.

Fish of the Week: Northern Snakehead (Channa argus)

Family: Channidae

Distribution: Native to freshwater river systems in China, Russia, North Korea, and South Korea.

Maximum Size: 4.5 ft

Not So Fun Fact: Because of its voracious appetite, scientists and fisheries personnel have been trying to keep the snakehead from invading the Great Lakes of North America.

Encyclopedia of Life: Northern Snakehead

The Northern Snakehead is a exclusively freshwater species that cannot tolerate marine environments. While most fish collect oxygen from water and breathe through their gills, the Northern Snakehead breathes through a modifed organ that allows it to breath air both in and out of water. Because of this, snakeheads can survive outside of water for days! 

Snakeheads have been introduced globally by human populations because they are considered to be an important fish for human food. Unfortunately, many of these introductions are not legal, and because the snakehead is capable of thriving out of water for days and is a voracious predator, the species has managed to invade numerous freshwater habitats all over the world. When populations of snakeheads are discovered in the United States, the government usually takes swift action to eradicate the individuals so the species does not threaten the native fishes of North America and damage ecosystems across the continent.


You can download or subscribe to our podcast on iTunes, follow us on Twitter, and tweet us your fishy questions @FM_WhatTheFish, or email us at whatthefish@fieldmuseum.org.

So long, and thanks for all the fish!

Fish Nerds Podcast Team:

Beth Sanzenbacher

Caleb McMahan (special guest, Biological Sciences graduate student, Louisiana State University)

Eric Ahlgren

Leo Smith

Matthew P. Davis


Science Focus: