In the movie Finding Nemo, the eponymous clownfish grows up in the security of his home reef and must find his way back after being fry-napped by an overenthusiastic diver. In reality, the larvae of clownfish spend their early lives adrift in the open ocean and only after weeks, or possibly months, do they return to the reefs where they were born. 

Their journey is guided by several cues that help them navigate home. The sound of a reef may be one of these but it’s clear that the most important sense for a returning fish is smell. Young fish have very well developed smell organs and respond appropriately to the molecules given off by other fish, and by