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Home > Resources & Publications > Newsletters & Magazines > Fins and Waters > 2008 > 04-08

Resources & Publications:  Fins & Waters

April 2008

Some folks may find it odd that the list also includes the red swamp crawfish Procambarus clarkii. Yes, that’s the main one in everyone’s crawfish boil around here. But this species isn’t welcome in areas that haven’t been part of its native range. In those places, the red swamp crawfish causes problems through burrowing – damaging irrigation systems, levees, dams and water control structures. It also acts as an intermediate host for some helminth parasites that may be limited in their reproductive capacity without this “new” species.

By this example, we see that the term “invasive species” has a lot in common with the term “weed.” According to gardeners, a weed is any plant that is growing somewhere where it isn’t wanted.

Unfortunately, plants and animals and even disease organisms are now traveling to more places where they are definitely not wanted. As an example of how fast species are being moved around the world now, the 2003 species list does not mention two of Louisiana’s newest aquatic invaders: the apple snail (genus Pomacea) and the Rio Grande cichlid fish (Herichthys cyanoguttatus).

Infestations of apple snails have occurred in several places in south Louisiana. Reports have described the invaders as one of two very similar species within the group called channeled apple snails: Pomacea canaliculata and Pomacea insularum. Originally from South America, this genus has been popular for food and for use in aquaria. Wild populations now cause tremendous damage to rice crops in Southeast Asia and the Dominican Republic. In the United States, this pest has become established in Florida, California, Texas, Georgia, Alabama and Hawaii. Even in locations where rice crops aren’t threatened, wetland vegetation can be damaged. Since 2006, the U.S. Department of Agriculture has banned the importation and interstate transport of most apple snails. However, some biologists have reported seeing the banned species in stores this year.

In 2006, apple snails were found near New Orleans in canals in Gretna. Attempts were made to control this infestation by aggressive removal and destruction of egg masses. Finding the bubble-gum-pink egg masses attached above the waterline on trees and pilings is a sure indication of the species’ presence, even where the fist-sized snail isn’t apparent. In the past few months, P. insularum has been found in huge numbers at locations near Houma. This outbreak is probably too extensive to control manually. Hoping for cold weather to kill this species won’t help, either. P. insularum is native to the Buenos Aires region of Argentina, where their average minimum monthly temperature in winter is 4–6 degrees Celsius (39–43 degrees Fahrenheit), which is actually colder than north Louisiana. In addition, channeled apple snails are relatively tolerant of estuarine salinity concentrations. We may be in the situation of hoping that there is an unknown factor which will limit this species in Louisiana.

Should they become established, the question will be raised on their edibility. Apple snails are popular as food in parts of Asia, but they are the intermediate host of several parasites. Anyone who tries one of the published recipes will want to cook them thoroughly.

Since about 1995, the Rio Grande cichlid is becoming more common in the waters in and around New Orleans. Known as the Texas Blue in the aquarium trade, this fish breeds readily in aquaria, and a number of folks have admitted to dumping excess fish into the canals. Now, people fishing for bluegills in City Park or Bayou St. John are as likely to pull up a Rio Grande as a native bream, and Rio Grandes have been found in bayous outside of the metropolitan area, including LaBranche. UNO researchers have found that the fish have no trouble living in Lake Pontchartrain at least long enough to infest nearby freshwater habitats. While this species originates from warmer locales, it seems to be doing fine in south Louisiana. And researchers are also finding that the Rio Grande can defend territory more aggressively than native bluegills, possibly leading to total displacement of native bream. While there is still some hope that conditions will develop that limit this species, people may want to investigate recipes for this one.

To learn more about preventing the spread of aquatic invasive species, visit www.protectyourwaters.net where the following procedures are explained:

  • Remove any visible mud, plants, fish or animals before transporting equipment
  • Eliminate water from equipment before transporting
  • Clean and dry anything that came in contact with water (boats, trailers, equipment, clothing, dogs, etc.)
  • Never release plants, fish or animals into a body of water unless they came out of that body of water

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