Behavioral adaptation to changing energy constraints via altered frequency of movement selection

Animal behavior is strongly constrained by energy consumption. A natural manipulation which provides insight into this constraint is development, where an animal must adapt its movement to a changing energy landscape as its body grows. Unlike many other animals, for fish it is relatively easy to estimate the energy consumed by their movements via fluid mechanics. Here we simulated the fluid mechanics of >100,000 experimentally-recorded movement bouts from larval zebrafish across different ages and fluid conditions as they hunted Paramecia. We find that these fish adapt to their changing relationship with the fluid environment as they grow by adjusting the frequency with which they select different types of movements, so that more expensive movements are chosen less often. This strategy was preserved when fish were raised in an unnaturally viscous environment. This work suggests a general principle by which animals could minimize energy consumption in the face of changing energy costs over development.