ATP is also a constituent of fish prey such as brine shrimp and plankton

Scientists in Japan have identified the olfactory receptor and brain circuitry that picks up the scent of adenosine triphosphate, or ATP. Although mostly known for carrying energy within cells, ATP is also a constituent of fish prey such as brine shrimp and plankton. 

The newly identified receptor is unique to fish and amphibians and is the gateway to initiating foraging behaviors in the zebrafish. Unlike other tested compounds, ATP activated neurons in the nose that are 'pear-shaped' and quite distinct from other olfactory sensory neurons. From there, the researchers traced the neural activation to one specific large glomerulus, or convergence of axons and dendrites in the olfactory bulb of the zebrafish brain. 

The lG2 glomerulus is highly sensitive to ATP and closely related compounds and in turn transmits the odor information to areas in the forebrain that are responsible for triggering the appropriate foraging behaviors.


Read more at: https://phys.org/news/2017-05-nasal-receptor-appetizing-fish-food.html#jCp