Fish Communicating Through Smell

Although vision is arguably the most important sense for most inhabitants of the coral reef, their sense of smell also has a key role. Odors may be detected a long distance from their source -- beyond the range of an animal's vision -- and can help, say, a predator locate a prey animal; for example, sharks are well known to home in on trace levels of blood in the water. When visual cues are misleading or confusing, a sense of smell can also allow animals to gather more information to help them decide what to do. Fish use their sense of smell to pick up the chemical messages passed between other animals.These chemical messages -- more correctly called pheromones (from the Greek "pherin" meaning "to carry") -- allow them to learn more about other members of their own species and to find mates.They also provide a host of other information, allowing fish to eavesdrop on their prey, their predators, and indeed all the other species that share their habitat.

Over what range can smells be detected?

A crucial stage in the life of a reef fish occurs when it makes the transition from a pelagic (free-living) larva to a juvenile, settled on a reef. Recent research has suggested that olfaction is extremely important in helping the larvae to find their way towards potential reefs and coral heads and to choose between them. But how do they decide which of the many options might make the best home? Many larval fish, such as humbug damselfish, are attracted towards the smell of other members of their own species. This makes good sense on the coral reef, because if a site is suitable for them, then it is also likely to suit the larva. The sense of smell can be used to navigate accurately over smaller distances as well. For example, settling larval clownfish can detect and home in on the smell of their host anemones over several feet.

How is the sense of smell used for identifying other reef animals?

The sense of smell is extremely important to clownfish, which lay their eggs at the base of their home anemone. While the embryos are developing, they seem to pick up the smell of this anemone and later in life, when they settle on the reef, they show a preference for the same anemone species. They can pick up its odor over considerable distances and home in on it using their sense of smell.

Is the sense of smell used in courtship on the reef?

Although the majority of courtship uses vision, in some species it can be triggered by smell alone. Small reef fishes are not highly mobile -- they tend to spend most of their lives within a relatively small area of habitat because of the risks involved in traveling conspicuously. For this reason, the arrival of a potential mate in the immediate vicinity is an opportunity too good to miss. Often, the first clue to the presence of a new fish is its smell; male frillfin gobies, for example, are known to react strongly to female pheromones. It has been shown that chemical cues alone are enough to provoke the excitable males into performing courtship behaviors, even when they cannot see the object of their affection.

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