What small pouches do fish use to detect smell in water?

Fish use olfactory sacs to detect smell in water. These specialized pouches are located on either side of the fish's head and are lined with sensory cells that are adept at capturing and processing odor molecules dissolved in water. When water enters the olfactory sacs, these sensory cells transmit signals to the fish's brain, allowing it to interpret different smells, which is crucial for finding food, avoiding predators, and navigating its environment.

In contrast, gills are primarily responsible for respiration, facilitating the exchange of oxygen and carbon dioxide rather than detecting smells. Swim bladders serve as buoyancy control mechanisms and are not involved in olfaction. Pectoral fins are primarily used for stability and movement rather than sensory detection. Thus, olfactory sacs are the key structures that enable fish to identify and respond to their chemical environment effectively.