Zebrafi sh occupy a variety of fresh water environments (Engeszer et al. 2007) in their natural habitat in South and Southeast Asia. They thrive in a broad range of temperatures, conductivities and fl ow rates, including 18°C cold, rapid fl owing rivers and 36°C warm and stagnant pools on rice fi elds, thus demonstrating great tolerance to different environmental conditions. They gather in shallow calm areas to mate and the females lay hundreds of eggs that are fertilised externally.