The Yellowhead Wrasse is a unique fish for a variety of reasons, but one of the most amazing is that it is actually able to capture and then kill crabs using the rocks and coral around it. This little fish was seen swimming along, repeatedly banging its prey on rocks and corals to stun or kill it so it can eat it.
It actually selects a rock and then bangs the small crab on it, drops the crab and adjusts it in its mouth for another smack. The fish swims on, repeats the process and it will eventually stop and eat the crab.
Crabs are a staple part of the Yellowhead Wrasse's diet but the claws and strong shell make eating it difficult. The Wrasse lacks the jaw strength to crush the crab. This use of rocks is a basic form of "tool use" once thought to exist in only humans and animals like Chimpanzees. It was believed that such complex thought could not be found in other animals. Using tools or other objects to an animal's advantage is similar to problem solving and requires a level of understanding that is quite impressive for a fish.
We now know that parrots and crows will drop hard shelled nuts on the ground where animals or cars will crush them. We are also seeing examples such as this where even fish are capable of understanding how to use objects around them to help gather and kill prey.
Another remarkable thing about this fish is that it starts life as a female. Throughout its life it will mate, breed and then eventually become male. After doing so, it can breed further. Interestingly, the fish will completely change color and size as it does this. This color change is not unusual for fish and even changing sex is not completely uncommon in other species. Parrotfish have been known to exhibit similar behavior. When a group of females loses the male, sometimes the dominant female will transform and become male.