Fish can smell their food, and this sense is highly developed for survival in the aquatic environment. Unlike humans who rely on air to carry scents, fish utilize the water itself to detect dissolved chemical signals. This ability allows them to locate food sources, identify mates, and avoid predators from a distance.
The Unique Mechanics of Fish Olfaction
The olfactory organs in most fish are distinct from their respiratory system; they do not “breathe” water through their nose. Instead, they possess paired structures called nares, or nostrils, typically located on the snout, that function solely for chemoreception. Each naris consists of an incurrent and an excurrent opening that channels water into a small, blind-ended olfactory chamber.
Inside this chamber is the olfactory rosette, a structure composed of numerous, highly folded layers of sensory tissue called lamellae. This folding increases the surface area available to detect chemicals, making the sense of smell more sensitive. Water is constantly circulated over this tissue by the beating of cilia or by the forward movement of the fish. Certain bottom-dwelling species, like flounders, can perform a behavior similar to “sniffing” by using accessory sacs or jaw movements to actively pulse water over the rosette.
Smell vs. Taste in Aquatic Environments
The distinction between a fish’s sense of smell (olfaction) and its sense of taste (gustation) is based on the distance at which the chemical signal is detected. Olfaction is a form of distant chemoreception, detecting dissolved chemicals like amino acids or bile salts from a food source far away in the water column. Smell is used for general orientation and tracking the source of an odor plume.
In contrast, taste is a form of contact chemoreception, requiring physical contact with the chemical stimulus to trigger a response. While fish have taste buds inside their mouth and throat, many species also possess external taste receptors on their lips, fins, and entire body surface. Catfish, for example, have sensitive taste buds covering their barbels, allowing them to “taste” the substrate directly as they forage.
Taste focuses on food recognition, confirming the palatability of an item once it has been located and touched. Both taste and smell are sensitive to water-soluble compounds, particularly amino acids released from potential prey items. Although both senses detect chemicals dissolved in water, they utilize different sensory organs and transmit information to separate areas of the brain, leading to distinct behavioral responses.
Olfaction’s Primary Role in Finding Food
The sense of smell is a primary tool for fish foraging, allowing them to locate food sources that are out of sight. When a food item is present, it releases a plume of water-soluble chemicals that spreads through the environment. Fish navigate by following this chemical gradient, a process often combined with rheotaxis—swimming against the current to move upstream toward the source.
Olfaction becomes important in environments where visibility is low, such as deep water, at night, or in turbid or muddy habitats. The chemical trail provides a reliable directional cue, which is often a fish’s earliest warning of an immobile or distant food source. This acute chemical sensitivity is strong enough that some fish, like anchovies, have been shown to mistake biofouled plastic debris for food based solely on the odor signature it acquires in the water.