Dictionary of Ichthyology  

holy fish = 2) sacred fish (1) various pools, wells and streams, particularly in the Middle East, contain fish that are purportedly sacred. There is s Pool of Sacred Fish (q.v.) at Şanlıurfa in southeastern Turkey. The temples of Apollo and Aphrodite in ancient Greece had sacred fish).

Chashma (= spring) in Nurata, Navoiy, Uzbekistan containing "holy fish" from Wikimedia Commons: http://commons.wikimedia.org/wiki/File:Holy_fish.JPG

Canadian Museum of Nature