Alligator Gar How are they spreading? They have spread to China and Japan because they are desired for aquariums. What impact do they have on the freshwater system they occupy? Alligator gar are accused by sport fishers of depleting stocks of game fish, such as bass, but all they do is eat what they can find. A positive impact they have is that they eat the silver carp, an invasive species, and are believed to eat Northern Snakehead, another invasive species.
Zebra Mussel How are they spreading? They stick to boats and hide in ballast water of ships, then are released elsewhere. What impact do they have on the freshwater system they occupy? They smother out other species of mussel, negatively affect the plankton food chain, clog pipes, grow on and cover other animals, etc.