Blue Ram (Mikrogeophagus ramirez)

The blue ram is a small cichlid native to the Orinoco River basin in Venezuela and Colombia. The fish forms monogamous pairs with both males and females displaying excellent parental care of their eggs and fry. Blue rams are popular in the aquarium trade, with several colour morphs existing.

Leonardo Dasilva and Miwok via Flickr

Oscar (Astronotus ocellatus)

The oscar fish is a species of cichlid native to South America. It is a popular fish in the aquarium trade, growing up to 45 cm and often perceived as intelligent. Several ornamental strains have been developed, including albino and long finned varieties. 

Elma on Flickr