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   Pomacea canaliculata (mollusc)     
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      Pomacea canaliculata in Cambodia (Photo credit: R.H. Cowie) - Click for full size   Pomacea canaliculata (Hawaiian) (Photo credit: R.A. Englund) - Click for full size
    Taxonomic name: Pomacea canaliculata (Lamarck, 1828)
    Synonyms: Ampullaria canaliculata Lamarck, 1822
    Common names: apple snail (English), channeled apple snail (English), Gelbe Apfelschnecke (German), golden apple snail (English), golden kuhol (English-Philippines), miracle snail (English-Philippines)
    Organism type: mollusc
    Pomacea canaliculata is a freshwater snail with a voracious appetite for water plants including lotus, water chestnut, taro and rice. Introduced widely from its native South America by the aquarium trade and as a source of human food, it is a major crop pest in south east Asia (primarily in rice) and Hawaii (taro) and poses a serious threat to many wetlands around the world through potential habitat modification and competition with native species.
    Description
    Large (up to 10cm), more or less globular freshwater snails. Aquarium trade snails are often smaller. Shell colour generally brownish or greenish, often with spiral banding patterns around the whorls. Some aquarium bred animals are bright golden yellow. Body colour can vary from dark, almost black to pale cream. Their presence is often first noted by observation of their bright pink egg masses laid on solid surfaces up to about 50cm above the water surface.
    Occurs in:
    agricultural areas, lakes, water courses, wetlands
    Habitat description
    P. canaliculata is widely distributed in lakes, ponds and swamps throughout its native range of the Amazon Inferior Basin and the Plata Basin. This amphibious animal remains submerged during the day, hidden in vegetation near the surface. It is more active during the night, and leaves the water in search for fresh vegetation. The activity rate of this snail varies highly with the water temperature. At 18°C they hardly move around, this in contrast with higher temperatures e.g. 25°C. Nevertheless, Pomacea canaliculata is more resistant to lower temperatures than most other snails from the genus Pomacea (The Apple Snail Website, 1998-2003).
    General impacts
    Pomacea canalicualata was originally introduced from South America to south-east Asia around 1980, as a local food resource and as a potential gourmet export item. The markets never developed; the snails escaped or were released, and P. canaliculata became a serious pest of rice throughout many countries of south-east Asia. In the Philippines, it is considered the number one rice pest and has caused huge economic losses. It was introduced to Hawai‘i in 1989, probably from the Philippines, and for the same reasons as for its initial introduction to south-east Asia. Again, the snails rapidly escaped or were released and quickly became major taro pests. P. canaliculata can spread rapidly from agricultural areas into wetlands and other natural freshwater systems where it may have a serious impact. These potential impacts could involve destruction of native aquatic vegetation leading to serious habitat modification, as well as competitive interactions with the native aquatic fauna, including native snails. Already, introduced P. canaliculata has been implicated in the decline of native species of Pila apple snails in south-east Asia. Also, native species of Pila in the Philippines are reported to have declined as a result of extensive pesticide applications against introduced P. canaliculata. Climatic modeling has shown that it has the potential to spread to many as yet uninfested parts of the world, for instance the huge rice-growing areas of India. It has already been introduced to the USA and threatens the major rice-crops of Texas and California. Australia in particular is extremely concerned about its potential introduction to natural wetlands (e.g., Kakadu) as well as to rice-growing areas.
    Notes
    The true identity of the pest species (perhaps more than one) is not completely clear, partly because the taxonomy of the group of species to which it belongs in its native South America is poorly understood. Much additional information can be found in Cowie, R.H. (2002) Apple snails as agricultural pests: their biology, impacts and management.
    Geographical range
    Native range: temperate Argentina northwards to the Amazon basin.
    Introduced range: Most of southern, eastern and south-east Asia, including the Philippines, Japan, Taiwan, Vietnam, Cambodia, Thailand, Laos, Korea, Sri Lanka, parts of Indonesia and Malaysia, southern China, Singapore; also Hawai‘i, Guam, and Papua New Guinea; the Dominican Republic; the USA (Florida, Texas, California).
    Introduction pathways to new locations
    Live food trade: Imported legally and illegally for development of aquaculture projects for human food.
    Nursery trade: Possibly introduced as eggs or small juveniles attached to aquatic plants.
    Pet/aquarium trade: Developed as a domestic aquarium snail and sold in pet stores.
    Smuggling: Illegally introduced, usually for development as a human food resource.


    Local dispersal methods
    Aquaculture (local): Deliberately moved in order to establish new aquaculture facilities. Probably accidentally dispersed as eggs or more likely small juveniles on agricultural products. Deliberately introduced to uncontained wetland systems in the hope of harvesting the snails for food.
    Escape from confinement: Escape (or even release) form aquaculture facilities is probably the major dispersal mechanism.
    Other (local): Release of domestic aquarium snails.
    Water currents: Probably one of the main means of dispersal within a watershed.
    Management information
    Preventative measures: The primary management approach must be prevention. Strict quarantine must be enforced to prevent introduction and spread. Incipient invasions must be eradicated rapidly while it is still possible to do this. For rice and taro fields, it is preferable to use plants from areas that are known to be apple snail free. If that's not possible, examine the plants and make sure that there are no apple snails or other unwanted snails and also check for egg clutches. The use of a screen on water inlets helps to retard the spread of apple snails. Screens should be cleaned regularly to obstruction. Around rice and taro fields, a barrier of copper could be used to slow the snail spreading to some extent. Copper is toxic to snails and they do not cross this material. The copper wire or strip should be placed above the water level, on the border of the field.

    Control: Eradication of established populations is probably not possible. Numerous measures have been tried in attempts to control apple snails in agricultural settings. These include: widespread use of pesticides, with serious environmental and human health consequences; biological control, notably the use of fish and ducks; a range of cultural and mechanical control measures. None has proven entirely effective, safe, and economically viable. None is likely to be appropriate in natural ecosystems. In rice and taro fields, hand picking is a successful method to control apple snail populations without harming the environment. The disadvantage is that it only works when done on regular base. The best results are obtained if the hand picking is done as a community effort. All visible snails should be collected with a scoop net or by hand. After collection the snails can be used for human consumption (beware of parasites!), crushed to serve as a food source for fish or destroyed otherwise. Eggs should not be forgotten during collection! Baited traps filled with lettuce, cassava and taro leaves can be used to attract the snails and to facilitate the collection. All vegetation and obstacles around fields should be removed as much as possible as the snails need this to deposit their eggs. When there are no suitable eggs-laying sites available, the snails are forced to deposit the eggs on the bare ground where the eggs are very vulnerable and easily fall into the water, which drowns the eggs. Before draining a field, make shallow trenches so that the snails will congregate in the trenches and can be captured easily.

    Nutrition
    A highly generalist and voracious macrophytophagous herbivore. Most plants are eaten, though it does show some preferences, for instance in Hawai‘i it will not eat water hyacinth.
    Reproduction
    Sexes are separate. Females lay clusters of bright pink eggs attached to solid surfaces (rocks, walls, logs, emergent vegetation, trash) up to usually about 50cm above the water surface. Eggs generally hatch within 7-15 days, but may take longer, probably depending on ambient temperature regime.
    Reproductive output can be enormous. Clutch size is up to 1000, but averages probably 200-300. Clutches are laid every few weeks.
    Lifecycle stages
    Longevity is up to 4 years. Reproductive maturity is reached in 3 months to 2 years, depending on ambient temperature regime.
    This species has been nominated as among 100 of the "World's Worst" invaders
    Reviewed by: Dr. Robert H. Cowie, Center for Conservation Research and Training, University of Hawaii, USA
    Compiled by: Dr. Robert H. Cowie, Center for Conservation Research and Training, University of Hawaii, Honolulu, Hawaii, USA & IUCN/SSC Invasive Species Specialist Group (ISSG)
    Last Modified: Wednesday, 13 April 2005


ISSG Landcare Research NBII IUCN University of Auckland