Jewelfish

Jewelfish were tiny, silvery fish with iridescent scales found in the rivers and lakes of Faerûn.

Ecology
Jewelfish were inedible by most humanoids. They were susceptible to changes in weather; if it became too warm, they would perish in large numbers.

History
It was once fashionable to dye jewelfish various metallic colors and keep them in garden ponds as decoration for the wealthy. The practice died out, but details of the process could be found in old books and guild archives in Waterdeep, Neverwinter, Memnon, and Esmeltaran.