''Retroculus lapidifer'' is a

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

cichlid Cichlids are fish from the family Cichlidae in the order Cichliformes. Cichlids were traditionally classed in a suborder, the Labroidei, along with the wrasses ( Labridae), in the order Perciformes, but molecular studies have contradicted th ...

native to

tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the souther ...

, where it is found in the rivers of the southeastern

Amazon basin The Amazon basin is the part of South America drained by the Amazon River and its tributaries. The Amazon drainage basin covers an area of about , or about 35.5 percent of the South American continent. It is located in the countries of Boli ...

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

. This fish was first described in 1855 by the French naturalist

Francis de Laporte de Castelnau Francis may refer to: People *Pope Francis, the head of the Catholic Church and sovereign of the Vatican City State and Bishop of Rome * Francis (given name), including a list of people and fictional characters * Francis (surname) Places *Rural ...

, who studied the fauna of South America while crossing the continent from

Rio de Janeiro Rio de Janeiro ( , , ; literally 'River of January'), or simply Rio, is the capital of the Rio de Janeiro (state), state of the same name, Brazil's List of Brazilian states by population, third-most populous state, and the List of largest citi ...

Lima Lima ( ; ), originally founded as Ciudad de Los Reyes (City of The Kings) is the capital and the largest city of Peru. It is located in the valleys of the Chillón, Rímac and Lurín Rivers, in the desert zone of the central coastal part of t ...

in an expedition starting in 1843 and lasting five years.

Description

''R. lapidifer'' can grow to a maximum length around . It resembles a marine snapper (genus ''

Lutjanus ''Lutjanus'' is a genus of marine ray-finned fish, snappers belonging to the family Lutjanidae. They are found in the Atlantic, Indian, and Pacific Oceans. They are predatory fish usually found in tropical and subtropical reefs, and mangrove for ...

'') in body shape and has five distinctive dark vertical bars on each side. The lips are large and underslung. The main body colour is an iridescent silvery-violet with random gold speckling. Small blue markings are on the face, two diagonal blue lines pass across the eyes, and an intermittent black spot appears on the soft part of the dorsal fin. Fish in this genus are characterised by a pointed snout, eyes set far back on the head, a depressed body with a compressed ventral region, and the ventral scales being smaller than those on the flanks.

Distribution and habitat

The species is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found els ...

to the southeastern Amazon basin in Brazil, where it is found in the

Araguaia River The Araguaia River ( pt, Rio Araguaia , Karajá: ♂ ''Berohokỹ'' eɾohoˈkə̃ ♀ ''Bèrakuhukỹ'' ɛɾakuhuˈkə̃ is one of the major rivers of Brazil though it is almost equal in volume at its confluence with the Tocantins. It has a tota ...

and

Tocantins River The Tocantins River ( pt, Rio Tocantins, link=no , , Parkatêjê: ''Pyti'' ɨˈti is a river in Brazil, the central fluvial artery of the country. In the Tupi language, its name means "toucan's beak" (''Tukã'' for "toucan" and ''Ti'' for "beak" ...

. It is typically found close to the bottom in rapids and fast-moving stretches of the river.

Ecology

''R. lapidifer'' forages on the river bed in fast-moving stretches of water, feeding on small

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s. Its diet varies with the time of year and the level of the river. When water levels are high, the main prey is chironomid midge larvae, but at lower water levels,

caddisfly The caddisflies, or order Trichoptera, are a group of insects with aquatic larvae and terrestrial adults. There are approximately 14,500 described species, most of which can be divided into the suborders Integripalpia and Annulipalpia on the ...

and

mayfly Mayflies (also known as shadflies or fishflies in Canada and the upper Midwestern United States, as Canadian soldiers in the American Great Lakes region, and as up-winged flies in the United Kingdom) are aquatic insects belonging to the order ...

larvae predominate. The fish has a large mouth and is more efficient at winnowing through the soft sediment than related species with smaller gapes. The

swim bladder The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ that contributes to the ability of many bony fish (but not cartilaginous fish) to control their buoyancy, and thus to stay at their current water depth w ...

is reduced in size in this fish and it spends much of its time hopping around and perching on the riverbed, propped up by its pelvic fins, in the manner of a

goby Goby is a common name for many species of small to medium sized ray-finned fish, normally with large heads and tapered bodies, which are found in marine, brackish and freshwater environments. Traditionally most of the species called gobies have b ...

. During feeding, it repeatedly dives head first into the sediment with its mouth open wide, and then expels sand through its

gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they ar ...

chambers. In readiness for breeding, a pair of ''R. lapidifer'' forms a nest about across in a gravelly area of the river bed. Adult fish have been observed carrying small pebbles in their mouths to build the nest, hence the specific name ''lapidifer'' (bearer of stones). A clutch of about 200 eggs is laid and the nest is guarded by both parents. They also turn the eggs and move them about to ensure aeration, and the eggs hatch in five to six days.

References

{{Taxonbar, from=Q5609388 Cichlinae Cichlid fish of South America Fish described in 1855 Taxa named by François-Louis Laporte, comte de Castelnau