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Swamp Eels

Belonging to the order Synbranchiformes, swamp eels are very slim fish with elongated bodies and reduced fins. Their gill system, which is very small, is linked to other organs to help them breathe air. Swamp eels live in tropical and subtropical habitats. They usually are found in stagnant fresh or brackish water; only one species lives in the sea. These fish are found in Central and South America, Asia, and Africa.

According to some publications, the order Synbranchiformes is made up of only one family, Synbrachidae, which contains four genera of swamp eels: the Macrotrema, the Ophisternon, the Synbranchus, and the Monopterus. Other sources report that there are three separate families within the Synbranchiform Order: the swamp eels, the singleslit eels, and the cuchias. Whichever way these fish are categorized, in total, there are about 15 distinct species.

Fish that look like snakes and live in dark, murky water are commonly called eels. Swamp eels are a great example of this type of fish. Indeed, they lack pectoral and pelvic fins, and their dorsal and anal fins are very small. Furthermore, while all species have small eyes, some are functionally blind with their eyes sunken below the skin. Some species live in caves, and many others burrow in mud. The maximum length these fish can attain is almost 3 ft (1 m). While swamp eels look a lot like eels, they are in no way related to them. Swamp eels are significantly different from eels internally and can breathe air. Furthermore, some of them estivate, which means that they sleep through the hot, summer months.

All 15 species of swamp eels have one or two gill openings at their throats which are designed to absorb oxygen from water. However, several species that live in water with small amounts of oxygen—like stagnant pools—are able to breathe air from the surface through their open mouths. One such species is the rice eel. Fish of this species live in rivers, ditches, and swamps of Southeast Asia, Indonesia, and the Philippines. During the extensive dry season, these fish burrow into the mud and can remain alive until the rainy season starts, as long as their skin remains damp. Interestingly, when rice eels reproduce, which is during the summer months, the males form the nests using air bubbles and mucus. As the female rice eels lay the eggs, the males pick them up, one by one, and spit them into the floating nests. The males guard their nests and eggs as they float freely in the water and stay with their young until they are independent. Rice eels have successfully adapted to living in rice patties and are an important source of food for people in some regions.

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Science EncyclopediaScience & Philosophy: Stomium to Swifts