''Nematobrycon palmeri'', commonly known as the emperor tetra, is a species of

characid Characidae, the characids or characins is a family of freshwater subtropical and tropical fish, belonging to the order Characiformes. The name "characins" is the historical one, but scientists today tend to prefer "characids" to reflect their sta ...

fish found in the Atrato and San Juan river basins in western Colombia. It was first imported in the aquarium trade to the United States in 1960 and has since become well established. Named in honor of Mervyn George Palmer (1882-1954), an English traveler who collected in Central and South America for the

British Museum The British Museum is a public museum dedicated to human history, art and culture located in the Bloomsbury area of London. Its permanent collection of eight million works is among the largest and most comprehensive in existence. It docum ...

, and who collected the type specimen.

Description

The purple hue of these

tetras Terrestrial Trunked Radio (TETRA; formerly known as Trans-European Trunked Radio), a European standard for a trunked radio system, is a professional mobile radio and two-way transceiver specification. TETRA was specifically designed for use by ...

will be more apparent in an aquarium with floating

plants Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude ...

on the surface and relatively subdued lighting. If the aquarium is too bright, the yellow coloration will dominate. The body is long, slim, and flattened to about 3 inches at maturity. Looking from the eye to the tail area, you will find a black line placed within a blue stripe. The sickled shaped dorsal fin, along with the pectoral fin and anal fins are yellow. The male is larger than the female and his anal fins are longer. The male caudal is more pointed than the female. Emperor tetras are highly sexually dimorphic and thus males and females are quite easily distinguished from each other. There are several ways to tell a male and female apart, the most reliable method is to observe the eye color. Males will have metallic blue eyes while females possess metallic green eyes. Also, the male has a three pronged tail with the medial black stripe usually extending beyond the rest of the tail, while in the females this median black stripe will typically only reach as far as the clear part of the tail. However, this is not always the best indicator as the third prong in males can sometimes be nipped off in competitions with tank mates and more dominant females may sometimes grow this extension of the tail as well. This species should not be confused with the royal tetra ''Inpaichthys kerri'', whose appearance and alternate common names resemble ''N. palmeri''.

Foods and feeding

The emperor tetra is an omnivore, eating both animal and vegetable food. Any good flake or pelleted fish food is a good basis for its diet. It will benefit from live food like daphnia and mosquito larvae as well as frozen fish food including frozen bloodworms.

Breeding

In a large well planted aquarium a single pair of emperor tetras will often breed without any extra stimulation. If there are no other fish, some of the babies may survive especially if the parents are well fed. In a large, well planted aquarium the babies will find some useful natural food in the form of protozoa, algae, etc. Screened daphnia will provide them with more nourishment as they grow, and dry fry food can be used.

In the aquarium

The emperor tetra is a placid aquarium fish and will be disturbed by more boisterous species. It grows to 4.2 cm. It prefers a pH of 6.5, a hardness of 3-6

dKH Degrees of carbonate hardness (dKH or °KH; the K is from the German ''Karbonathärte'') is a Units of measurement, unit of Hard water, water hardness, specifically for temporary or carbonate hardness. Carbonate hardness is a measure of the conce ...

and a temperature of 23–27 °C. It does not school as readily as most tetras, and a pair appears happier than with most tetras. However, with the addition of fresh cool water, a large group of emperors will school across an aquarium, sometimes for several minutes.

Gallery

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References