Why donít fish get lost in the ocean?
Fish have all sorts of senses that they use at different stages in their lives to know where they are; they can smell, they can hear, they may have the ability to sense magnetic fields. Because Fish eggs float around coral reefs, you would expect to get a mix of genetically different fish on different reefs, but research shows that there are clusters of fish that stick to the same reefs.
Reefs are actually very noisy - you can hear fish nibbling at coral, and things like snapping shrimps adding to the noise. By making artificial reefs and playing this noise in some, but not in others, researchers saw that fish would stay around the noisy reefs - proving that the fish could hear the reef. There is also evidence that fish can smell similar fish - which could be how salmon know which river to return to.