How do fish smell

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The title of this post could be taken two ways. I was temped to simply write BAD in big black letters, but April fools is long gone (thankfully), and fish don't really smell that bad.

The sense of smell is extremely important to a fish. It gives them ability to smell out food and in some cases return to the correct breeding location years after leaving "home." The salmonoid family of fishes can detect a certain amino acid in quantities as little as 1 part per 8 billion, which is quite amazing really. This ability means that fish are just as easily put off by smells they are unfamiliar with. The can include the following sunscreen, motor oil and petrol.

How do fish smell
Fish don't have nostrils like mammals, but have a very similar set of holes called nares which lead into a chamber full of sensory pads. The fish smells by moving water through this chamber and over the sensory pads and in general the faster the water moves through the better the sense of smell. Most fish need to keep swimming for this to occur, but some fish can pump water through the system via tiny hairs called cilia or through muscle movement. When the sensory pads pick up a smell they transmit the signal to the brain for interpretation, which the fish ultimately responds to.