The olfactory organs are paired olfactory sacs that open outward through the nostrils on the front of the head. At the bottom of the nasal cavities are sensitive cells (receptors), up to 95,000 per 1 mm2. Many fish have an extremely fine sense of smell. It is especially developed in the passage fish and fish, leading a nocturnal and crepuscular lifestyle. Extract of moth fish recognize in dilution 1 · 10-9 , fear pheromones pick up at a concentration of 10-10. Olfactory receptors, in addition to chemical perception, also perceive mechanical effects, temperature changes.

Smell and taste allow fish to orient themselves in the chemical composition of the environment. The ability of fish to sense chemical signals is well illustrated by salmon, which, going to spawn from the sea to river systems, determine by the smell of the water exactly the stream or river in which they themselves once emerged from the eggs. The olfactory receptors of fish are located in the nostrils. Unlike the nostrils of other vertebrates, they are not connected to the nasopharynx (only bipedal fish have choanas).