Jewelfish

Jewelfish were a tiny, silvery fish found in the oceans and rivers of Faerûn.

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

History
It was once fashionable to dye jewelfish various colors. The practice died out, but details of it could be found in old books in Waterdeep, Neverwinter, Memnon, and Esmeltaran.