Pacific trumpetfish have the ability to change their coloration according to their surroundings. In this case, the trumpetfish has turned yellow to blend in with a shoal of yellow tang, one of the most common fish on the reef.
So why bother with this subterfuge? Trumpetfish are predators, feeding mostly on small fish and some crustaceans. Appearing to be one of the crowd allows it to sneak up on unsuspecting prey. And while the very different shape of the trumpetfish might make it seem like it’s prey would be sure to spot it, from the front, which is where the prey is going to be, trumpetfish are very hard to spot.