Inner ears for hearing
Fish hear through their inner ears despite having no visible external ears. In most bony fish, each inner ear contains three otoliths, small mineral structures: there are three pairs, not three in total.
Relative movement between these structures and the tissues supporting them stimulates sensory cells. This system contributes to hearing and balance. In some species, the swim bladder also transmits vibrations towards the ear and improves detection of certain sounds. This connection is not present in all fish.
Smelling dissolved substances
Water passing through the olfactory organs on the snout brings dissolved molecules. Sensory cells detect them: this is smell. These openings do not serve for breathing as our nostrils do.
Depending on the species, chemical information contributes to finding food, reproduction or detecting danger. Some species respond to substances released by an injured fish. This mechanism should not be attributed to all sardines or anchovies without evidence for those species.
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