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Stuff already there: Centrocestus formosanus

Centrocestus formosanus is a trematode parasite of Asian origin that has found its way into North American streams and rivers. It not only affects the fountain darter but many species of commercially important fishes.

The parasite is transmitted via a freshwater snail Red-rimmed melania Melanoides tuberculata that was introduced in the United States and Mexico in the 1960s. The parasite is believed to have been introduced from shipments of black carp to fish farms in Mexico. The definitive hosts of Centrocestus formosanus appear to be piscivorous birds that migrate along the central flyway from South America to North America.

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Life Cycle
C. formosanus shares a similar life cycle to others within the family Heterophyidae. Miricidia develop in eggs for around 12-15 days in the environment outside the definitive host. Snails are the first intermediate host and they get infected by the parasite by consuming embryonated eggs from the feces of a definitive host. Snail species Semisulcospira libertine, Melanoides tuberculate, and Stenomelania newcombi are common first intermediate hosts. Sporocysts develop from the miricidum and are found in the mantle tissue of the snail host. Rediae develop from the sporocysts and migrate to the digestive tract. It takes around 90 days from start of infection to develop into cecaria, the motile larval stage. Cecaria then leave the first intermediate host and swims till it encounters fish, which are its second intermediate host. In their second intermediate hosts, they develop into metacecaria and encyst on gill filaments. Many different species of freshwater fish have been found infected by C. formosanus, including species of ray-finned fish, carp and tilapia. When the second intermediate host is consumed by the definitive host, a mammal or a bird, they mature into adult worms. Adult worms reside in the small intestine of the definitive host. They become able to reproduce after about a day in the definitive host. Piscivorous bird and mammal species are the parasite's natural definitive host. This contains various species of herons. Other natural definitive hosts include ducks, chickens, dogs and foxes. Some species have been experimentally confirmed to be capable of being infected by C. formosanus, including rats, cats, and rabbits. Humans have sometimes been found to be naturally infected.

Morphology
The species of Centrocetus are defined by the amount of circumoral (circling the mouth) spines. C. formosanus typically has 30-36 circumoral spines, with 32 being the most common number of spines. These spines are laid out in two rows. The adults are typically around 0.45 mm long and 0.20 mm wide with a flask shaped body. Their acetabulum is located in the middle of their body and their oral sucker on the anterior end of the body. Inside their mouth they have a prepharynx which leads into a pharynx and then into a short esophagus. C. formosanus are hermaphroditic and one will contain both ovary and testes. Their testes are located near the posterior end of the body, opposite of each other. They are oval shaped and lobed. The ovary is located directly above the testicles. The Cercarie stage have a heart shaped body with a tail. They have two eyespots opposite each other near the anterior end of the body but below the oral suckers. They have two rows of 4-5 hooklets around the mouth.

Distribution
This species was first described in Taiwan. Its current range exists in the continents of Asia (China, India, Japan, Laos, The Philippines, Taiwan, Thailand and Vietnam), Europe (Croatia and Turkey), Africa (Egypt and Tunisia), North America (USA and Mexico), and South America (Brazil and Costa Rica). Its introduction to Mexico was most likely through the snail Melanoides tuberculate infected with the sporocyst stage of the parasite that came by way of shipments of black carp from China in the 1970s. Melanoides tuberculate is also the only species of snail used as the first intermediate host in every country the parasite is found.