Obscure Swamp Eel, Ophisternon aenigmaticum
Obscure Swamp Eel, Ophisternon aenigmaticum. Fish caught from coastal waters off Belize, June 2020. Length: 54 cm (21 inches). Catch, photograph, and identification courtesy of Josh Leisen (joshadventures.com), Gaylord, Michigan.
The Obscure Swamp Eel, Ophisternon aenigmaticum, is a member of the Swamp Eel or Synbranchidae Family, that is known in Mexico as anguila falsa. Globally, there are six species in the genus Ophisternon, of which one, this species, is found in the Mexican freshwater systems that are part of both the Atlantic and Pacific Ocean drainages.
The Obscure Swamp Eel has an elongated, stout, and snake-like body that ends in a broad flat tail. They are covered with small inconspicuous blotches. They are a uniform dark olive brown color without markings. Their gill openings are far forward on underside of head. They do not have pectoral or pelvic fins. Their head is large and bulbous and tapers to a rounded snout. They have small eyes placed well forward on their head.
The Obscure Swamp Eel is found in freshwater and brackish waters of swamps, lagoons and permanent or temporary floodplain ponds, arroyos, caves, lakes, rivers and sulfur springs that can range from clear to muddy with moderate or no current that have clay, gravel, mud, rock or sand substrate and are heavily vegetated at depths up to 2 m (6 feet). They move by swimming in water or crawling on land via anguilliform locomotion whereby its entire body moves in a series of sinuous waves from head to tail. The Obscure Swamp Eel has a keen sense of smell and feeds on anelids, crustaceans, fishes and snails. They are capable of breathing air through their skin and gills and can survive long periods out of water. They reach a maximum of 80 cm (2 feet 7 inches) in length. They are night time predators and retreat to dens within weeds, heavy grass beds and water hyacinth in the substrate or caves during daylight hours often burying themselves. They are hermaphrodites with each eel having both male and female reproductive organs. Their young are born live and are between 5.0 cm (2.0 inches) and 7.2 cm (2.8 inches) in length. The Obscure Swamp Eel is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.
The Obscure Swamp Eel is found within the Atlantic Slope of Mexico from northwest Veracruz to southern Tabasco; they are also known to the Pacific Slope in Chiapas.
The Obscure Swamp Eel is most likely confused with the American Eel, Anguilla rostrata (have rayed anal, caudal and dorsal fins and pectoral fins).
From a conservation perspective the Obscure Swamp Eel is currently considered to be of Least Concern with stable, widely distributed populations. Their long-term survival is threatened by human development that includes pollution, habitat degradation and alteration, sedimentation, and invasive species. In contrast these eels are difficult to eradicate from some locations.