Cardinal tetras are famous for their glowing blue and bright red stripes that run across their bodies. People often mix them up with neon tetras, but cardinal tetras have a bright red line that goes ...

Guppies in the wild have evolved over at least half-a-million years -- long enough for the males' coloration to change dramatically. Yet an orange patch on the male has remained remarkably stable. Why ...

When Robert Heathcote dips his head into the rivers of Trinidad, he’ll often see little black dots moving through the water, even when it’s murky. Those dots are the eyes of small, inch-long fish ...