The blackstripe coris, also known as the yellowstripe coris, is an endemic wrasse. According to my fish book, John P. Hoover’s The Ultimate Guide to Hawaiian Reef Fishes, Sea Turtles, Dolphins, Whales, and Seals, it’s most abundant around the northwestern islands of the Hawaii chain. Around the main islands, mature females are uncommon and males rare.
The fish in the top photo is a large male. It has no black stripes, yellow stripes, or stripes of any kind, because this is one of those species where the male and female look radically different. This male was sparkling green in a variety of patterns. The other photo shows a female, which gives a better idea of why the fish got its name.