| There are three things that are important in the life of a fish (or any other organism for that matter). One: to acquire something to eat. Two: to avoid being eaten. And three (if you succeed in getting enough nutrients and steer clear of your hungry neighbors): to reproduce. One thing that can help a fish to achieve the first two objectives is to look like something that it is not, like an algae encrusted rock or a toxic sponge. This antipredation/feeding adaptation is referred to as camouflage or crypsis.
The leaf scorpionfish sways from side to side to enhance its crypsis as shown in the animation right.