Aphyosemion australe, sometimes called the Lyretail Panchax (although that name is also applied to several other, related species) is a beautiful, small species of African killifish. These fish are very easy to keep, with a 5 gallon tank being sufficient for a pair. These fish appreciate temperatures between 70-75 Fahrenheit, so a heater is not necessarily required unless your house is cool. They were one of the first killifish that were kept in the aquarium hobby. As such, there are many selectively bred strains available, as well as many naturally occurring localities. This strain, the 'Hjersseni', is a selectively bred xanthic (excess of yellow pigment) morph, developed in the 1950s.
These are young individuals, around 3/4" long. They are showing sexual dimorphism, but the male's colour will get more intense as they grow.