Emperor Tetra Nematobrycon palmeri

The Emperor Tetra is native to slow waters of the Atrato and San Juan river basins in western Colombia. It is unusual for a tetra in not having an adipose fin on the back and is one of the few characins which grows a central projection to its tail fin - usually only on males. Males also have blue irises whereas females have green. Males of the only other member of the genus have red irises.

They grow to some 4cm long. The Black Emperor Tetra, above centre and right, used to be considered a related species (N. amphiloxus) but is now classed as a variant of the same species.

The Black Emperor, above, has more black on its flank and is darker. The smaller Kerri Tetra is sometimes called the Blue or Purple Emperor but is a different genus (and has an adipose fin). Emperors scatter eggs on plants and leaves, one at a time, when spawning and show no parental care.