Rivulus marmoratus
FAMILY
Rivulidae
TAXONOMY
Rivulus marmoratus Poey, 1880, "from Cuba, if they do not exist in the United States." Poey's description of the type locality has to be one of the strangest in the history of taxonomy. As it turns out, this species is found in Florida and Cuba; the types are presumed to be from Cuba, Poey's homeland.
OTHER COMMON NAMES
English: Rivulus.
PHYSICAL CHARACTERISTICS
Grows to 3 in (75 mm) in length. Hermaphrodites. Cylindrical in shape, with tapering of the head and caudal peduncle and a high scale count. Dorsal and anal fins are set far back (typical for all Rivulus species), with the dorsal fin origin set back farther than the anal fin origin. A characteristic splotchy brown pattern, with an irregular dark mark just behind the operculum (humeral blotch) and a rivulus spot (ocellus) on the caudal peduncle. Primary and secondary males have the same body shape, an orange or pink overlay (more often orange) on the body and fins, mottling, and a dark humeral blotch. The rivulus spot sometimes is absent, unpaired fins at times are clear and at times have dark edges. The proportion of primary males in Belize is high (25%), whereas elsewhere the proportion is very low for both primary and secondary males.
DISTRIBUTION
Florida, Mexico, Belize, Nicaragua, Guatemala, Honduras, French Guiana, Venezuela, Brazil as far south as Santos, the Bahamas, and numerous Caribbean locations.
HABITAT
A semiterrestrial species that inhabits coastal mangrove forests in very shallow water or the wet areas of their muddy flats, out of water under detritus and leaf litter, or under or inside rotting logs. Frequently occurs in the burrows of land crabs. Found in marine and brackish water or in hypersaline pools but not in freshwater.
BEHAVIOR
Can be caught in traps set in crab holes but dies if the traps become flooded, possibly indicating that respiration of atmospheric air is a necessity. They also can be caught on a tiny hook baited with a small piece of worm. Captive individuals jump out of the water to snatch a termite or ant held above the water surface. In nature they flip along the water surface one or more times or leave the water altogether to elude danger. Extremely aggressive toward each other in aquaria, yet small aggregations have been caught in crab burrows and under rotting logs.
FEEDING ECOLOGY AND DIET
Feeds on small terrestrial and aquatic insects, mosquito larvae, polychaete worms, mollusks, and gastropods. It leaves the water to seize food items but returns to the water to eat them.
REPRODUCTIVE BIOLOGY
The only known self-fertilizing vertebrate. Although they are highly efficient at self-fertilization, hermaphrodites release some unfertilized eggs. There is evidence that outcrossing takes place, which would seem to indicate that the hermaphrodites can suppress self-fertilization so that males can fertilize the unfertilized eggs released by the hermaphrodites.
CONSERVATION STATUS
Not listed by the IUCN. Regionally are listed as a species of Special Concern in Florida.
SIGNIFICANCE TO HUMANS
Widely used in field and laboratory studies in genetics, toxicology, ecology, and physiology.
