Most of these fish may not fly the freak flag as we know it, but all of them are invasive species that are dominating an environment in which they are not native–and adversely affecting the habitat they now call home. This year Food & Water Watch, the non-profit that helps people navigate making safe and sustainable food and water choices, has included invasive species in their Smart Seafood Guide–with the idea that adding invasive species as a menu item may help to control their populations at less destructive levels. And with so many other aquatic species being overfished to the point of extinction, it may be an idea whose time has come. What do you think? Asian swamp eel for dinner?
Following are 9 invasive species as Food & Water Watch has described in the new guide.
1. Asian carp (Midwest and Great Lakes regions)
Asian carp, as they are known in the United States, actually includes several different species, including the bighead, black and silver carp. Asian carp species are not bottom feeders, and so are generally lower in contaminants than the common carp. Although the FDA has not yet evaluated these fish for contaminants, they are believed to be low in mercury. These fish are native to Asia and were brought to the United States primarily by catfish farmers in the 1970s to control algal blooms in aquaculture ponds. Today, Asian carp have spread through major waterways from the Southeast through sporadic flooding events, and have moved toward the Great Lakes regions. Asian carp are a problem because they are prolific spawners, grow and mature quickly, and feed on both plant and animal plankton. Silver carp, for example, may consume two to three times their own body weight in algae and phytoplankton each day — throwing off ecosystem balance. Asian carp may compete with other native fish populations in the lakes and ponds of the Midwest. Asian carp can be caught with cast nets, hand nets or occasionally on hook and line.
2. Asian shore crab (East Coast states from Maine through North Carolina)
Asian or Japanese shore crab is native to to parts of Russia and Japan, but has become invasive along the East Coast, from Maine through North Carolina. It was probably introduced into the United States by international ship travel. Asian shore crabs are small, usually measuring not more than an inch and a half across, but are opportunistic feeders and will consume small fish, crustaceans, algae and anything else they come across. Its primary negative impact as an invasive species is displacement of native crab populations, as it competes for similar habitat to native blue crab, rock crab, and lobster.
3. Asian swamp eel (Hawaii, Georgia, Florida)
Asian swamp eels are native to many parts of Asia, and are currently listed as invasive in three states: Hawaii, Georgia, and Florida. In New Jersey, their status is listed as unknown but they have recently been found there. The eels’ introduction to the wild probably took place accidentally in the Southeast (from an aquarium or fish farm escape) and they may have been introduced as a food fish in Hawaii by immigrants. They have no known predators in North America. The eels are highly adaptive, can live in just a few inches of water, and can travel short distances on dry land. They are predators, feeding on insects, worms, fish, crustaceans and small amphibians — but can also survive for weeks without food. All of these traits make them especially risky as an invasive species. In particular, there is concern that populations of Asian swamp eels have been found within a mile of Florida’s Everglades National Park; if these eels manage to establish themselves in that sensitive ecosystem, it could displace threatened native populations and vegetation. It is a popular food fish in Asian cuisine and has a meaty texture. Contaminants unknown, no incidents reported.
4. Chinese mitten crab (California and New Jersey)
The Chinese mitten crab is native to Southeast Asia but was introduced to California in the early 1990s, probably by way of international ship travel. It is now established throughout many California water networks surrounding the San Francisco Bay, and also in New Jersey, with several other states reporting sightings. The crabs are edible, and considered a delicacy in some cultures. They are imported live, sometimes illegally, as the sale of these crabs is prohibited in certain states. Release of live crabs from these shipments may be another means of introduction. Ecologically speaking, Chinese mitten crabs are a nuisance in non-native areas, especially in urban areas, and may clog water pumps and hamper water delivery. They also burrow into soil, which can exacerbate riverbank erosion and weaken levees. The mitten crab eats a variety of plant and animal materials, which may harm recovery efforts of endangered species in the California delta; they are also a problem for rice farmers, as the crabs can damage the rice crop in flooded fields by eating young shoots. Although there is limited data, testing on Chinese mitten crab captured in California has revealed low levels of chemical contaminants20; there is little data on New Jersey populations of this species.
5. European green crab (Eastern and Western Coasts of U.S.)
The European green crab was introduced to the East Coast of the U.S. in the early 1800s, probably by way of ship travel. In the late 1980s, the crab was discovered on the West Coast, and invasive populations have since become established from California through Washington and up into British Columbia. The European green crab is a small but voracious predator, and it is able to outcompete other crabs for food and habitat. It eats a variety of small crustaceans (including the young of commercially important crab populations), algae, and shellfish such as oysters, clams and mussels. They can be caught in traps or collected from shellfish operations (they are a nuisance to these facilities). Although the FDA has not yet performed testing specifically on this species for contaminant levels, academic studies suggest that it does not contain levels of mercury or PCBs that can be harmful to human health, because it is especially sensitive to these contaminants itself. Although the meat yield from a green crab is somewhat lower (because they are smaller than other types of crab), it can be eaten like any other kind of crab — in soups, seafood bisque or crab cakes.
The lionfish is a tropical fish native to a wide range of regions in the western Pacific Ocean. Since the early 2000s, it has become an established invasive species on the East Coast of the U.S. and in the Caribbean, probably as a result of people releasing aquarium fish in coastal waters. The lionfish is fast-growing, a voracious eater, reproduces yearround, and has no known predators in the areas to which it has now been introduced, so it is quickly becoming a threat to local ecosystems, especially along the central and south Atlantic coasts. Because it is not native to the U.S., it has not traditionally been considered a food item there; however, in areas where it is native, such as the Red Sea between Egypt and Saudi Arabia and many islands in the Pacific, the fish are regularly consumed. Because they are slow moving, lionfish are typically caught with spears or hand-held nets, a catch method that is very selective and results in little bycatch or damage to habitat. Although its spines are venomous, they are easily removed after capture and the poison in them is neutralized by heat, as through cooking. The lionfish is a whitefish and is said to taste similar to certain snappers and groupers.
7. Rusty crawfish
The rusty crawfish is native to Kentucky, Ohio and Indiana, but it has become invasive in at least 17 states throughout the U.S., from Maine to New Mexico. Because it is a popular baitfish, this crawfish has probably been introduced into new waters accidentally by recreational fishing. Most people may not be familiar with the risks that these creatures can pose to new environments. Rusty crawfish can establish themselves in new areas easily, as females can lay 500 eggs or more at a time. The rusty crawfish is a voracious and opportunistic eater, and can change the ecology of regions it invades by reducing the abundance and diversity of plants and aquatic life where it lives. Because it can eat twice as much as native crawfish, it also has the potential to outcompete and overtake the local crawfish population. The rusty crawfish is caught for commercial consumption in some areas, and can be eaten like any other type of crawfish. Because they live in the mud, crawfish are generally purged in fresh water for several hours prior to eating to flush out any contaminants. However, care should be taken to adhere to state laws, some of which prohibit the capture of live rusty crawfish (which means they can’t be adequately purged before cooking). Contaminants unknown, no incidents reported.
8. Tilapia, Mozambique and blue
Two populations of tilapia have been introduced to the U.S. through escapes from fish farms — the Mozambique tilapia, which is native to southern coastal Africa, and the blue tilapia, native to the Middle East and parts of Northern Africa. These fish are now established throughout many warmer southern states from Hawai`i to Florida. Tilapias can tolerate a wide range of salinity, and so can live in freshwater or marine habitats (and everything in between). Tilapias can be a threat to native species because of competition for food and habitat; the presence of invasive tilapia populations can lead to declines in wild populations of native fish. Tilapia is white-fleshed and mild-flavored, and a popular food choice in many countries. It is already growing in popularity in the U.S. Contaminants unknown, no incidents reported.
9. Walking catfish (Florida)
The walking catfish is native to Southeastern Asian countries, but has become invasive in southern Florida, and is at risk for becoming invasive in other states. It was introduced to the U.S. in the 1960s, probably as a result of the aquarium trade, and after attempts to farm the fish commercially here. The walking catfish is unusual because it is able to live out of water for short periods, and even to move short distances over land. This allows it to take advantage of flooded fields, canals, and even rainy days to expand its territory. This fish has previously invaded several eastern coastal states and Nevada, but as of 2011, has been eradicated from all locations except for Florida. Like many types of aquatic invasive species, the walking catfish is a voracious eater and will consume a wide variety of foods including small fish, insects, plant material and detritus. Its eating habits may help it to outcompete other predators in ponds and it can quickly establish itself as the dominant species in new areas. This type of catfish is viewed as a delicacy in much of Southeastern Asia, and especially in India — and can be eaten as any other type of catfish. Contaminants unknown, no incidents reported.
More from Food & Water Watch
See the Smart Seafood Guide: Dirty Dozen for the fish that fail.