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Rummy-nose tetra

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The rummy-nose tetra, Hemigrammus rhodostomus, is a species of tropical freshwater characin fish originating from South America, popular among fishkeepers as an aquarium fish. one of many small tetras belonging to the same Genus, it is a 5 cm long fish when fully grown, and is a long established favourite among tropical fishkeepers. The fish is one of several very similar species including Hemigrammus bleheri Géry & Mahnert 1986, and Petitella georgiae Géry & Boutiére 1964, and it is possible that more recently collected specimens available in the aquarium trade are members of one or other of these alternative species. The common name applied to most of these fishes is “rummy-nose tetra”, though other common names are in circulation (such as “firehead tetra” for H. bleheri, according to FishBase).

The rummy-nose Tetra is a torpedo-shaped fish, whose basal body colour is a translucent silvery colour suffused in some specimens with a greenish tint: iridescent green scales are frequently seen adorning the fish at the point where the fontanel (a part of the head roughly corresponding to the forehead in humans) meets the body. The fins are hyaline, with the exception of the tail fin, this fin being adorned with black and white horizontal stripes, variable in number, but usually comprising one central black stripe in the central portion of the tail fin, with two horizontal black stripes upon each caudal fin lobe, the spaces between the stripes being white, the total count of black stripes being five. The head is a deep red colour, iridescent in lustre, with the red continuing into the iris of the eye, and some red colouration extends beyond the operculum or gill plate into the anteriormost section of the body proper. Some specimens classified as Hemigrammus rhodostomus possess three black tail stripes instead of five, and some specimens classified as Petitella georgiae have a black stripe in the caudal peduncle extending forwards into the body, surmounted above by a thin iridescent gold line: however, whether these features are reliable determinants of species identity has yet to be fully ascertained.

Male and female individuals exhibit no obvious visual differences, other than increased fullness of the body outline in ripe females.

The three different species of fish thus known as Rummy-Nose Tetra have the following distributions:

All three species of rummy-nose tetra inhabit river stretches whose water chemistry is mineral-deficient (soft), acidic, and frequently tainted with humic acid decay products from leaf litter upon the river substrates (known as ‘blackwaters’ because of their appearance). Aquatic plants are sometimes present in these stretches of water, though the upper reaches of the Rio Negro are less densely populated with aquatic flora than the other rivers due to shading from the rainforest canopy. The fishes preferentially inhabit the middle and mid-lower water regions.