Young snakeheads are brownish-red and slender with stripes. The problem is that they don't stay young and slender, and get too large for aquariums. Adults have light bellies and dark backs, and their heads look like snakes, with many sharp and spiked teeth. So people are no longer fascinated, and dump them into ponds and other freshwater bodies of water.
With other freshwater aquarium fish such as goldfish, releasing them into the wild isn't a problem―they just blend in with other fish species and become new natives to the area, predators of smaller fish and prey of larger fish.
Snakeheads are capable of spawning up to five times a year. Because they can produce up to 50,000 eggs in each spawning, they are able to totally decimate native fish species, including popular game fish such as trout and bass.
They have adapted through the years to survive in water that has little oxygen, and as a result, they can crawl for short distances across land, using their fins to balance, breathing in oxygen through small bronchial appendages.
Although they will not attack humans they may encounter on land, they may cause injury to anyone who steps on them. However, adult snakeheads are very vigorous in protecting their young. One species of snakehead reportedly attacks people, and has occasionally killed humans who approached their brood.
So far, there have been snakeheads captured in northern California, Maryland, Massachusetts, Rhode Island, and Maine areas, where the climate is not conducive to the maintenance of a population.
But if a snakehead is ever released into the subtropical waters in Hawaii or Florida, chances are that the fish would be able to successfully reproduce, and many endangered species in the United States―as many as 115 species of fish, 16 amphibians, and 5 endangered crustaceans―would be affected or become extinct.