Brown and gray with stripes on its fins, back and tail. In the fall when the streams are filled, female and male o'opu go downstream to mate. The females lay eggs near rocks for protection. The eggs stick to the rocks and males fertizlize them by covering the eggs with sperm. The male o'opu guard the eggs until they hatch, which takes about one day. O'opu larvae cannot live in freshwater long, so the larvae floats downstream to the ocean. The O'opu nakea is a freshwater fish that feeds on small insects, seaweed (limu), snails and earthworms. O'opu may also eat other o'opu nakea and plankton.