rednosed tetra

The rummy-nose tetra has a maximum total length of 5.0 cm (2.0 in). It has a fusiform body shape, 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 meets the body. The fins are hyaline, with the exception of the caudal fin. This fin is 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 are white, the total count of black stripes is five, or occasionally three; however, whether these features are reliable determinants of species identity has yet to be fully ascertained. 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 into the anterior-most section of the body proper. Male and female individuals exhibit no obvious visual differences, other than increased fullness of the body outline in ripe females.

The rummy-nose tetra is found in South America, where it is endemic to Brazil's Pará state in the Amazon basin. Records from the Orinoco are thought to refer to P. bleheri. This species is found in 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. The fish prefer darker waters, as there is evidence of the eggs and fry being light sensitive.

Rummy-nose tetras present serious challenges even to experienced aquarists from the standpoint of breeding, primarily due to two factors: the likelihood of sterility ensuing if the prospective parents are maintained in water with too high a level of dissolved calcium ions, and the slow growth rate of the fry. An additional problem is that gender differentiation is difficult by visual inspection alone, making pair selection partly a matter of luck unless an obviously gravid female is available for selection. Again, identical remarks apply to all three species listed above. The breeding aquarium for the rummy-nose tetra, in addition, needs to be sterilised prior to use, as the fish produces eggs that are notoriously sensitive to bacterial and fungal infection. Use of an antifungal agent is strongly advised once spawning is completed in order to prevent various fungi from attacking the eggs. Needless to say, given the above remarks about likely sterility if the fishes are maintained in water whose chemical parameters are incorrect, prospective parents must be maintained in soft, acidic water throughout their lives if they are to remain capable of reproduction. Failure to do so will destroy any chances of success from the very start. …

The rummy-nose tetra is classified in the genus Petitella. This name suffixes the Latin diminutive -ella onto the surname of the French zoologist and anatomist Georges Petit, who was director of the Laboratoire Arago in France. The specific name, rhodostoma, is derived from the Greek rhodon, a "rose", and stóma, which means "mouth" — an allusion to the red colour around the nose and mouth.