Why do fish not willingly haunt very deep water?
Because, even in summer, it is of very low temperature, approaching to 40°, and it contains little or no vegetable food or insects, which the smaller fishes search for; and the larger fishes follow the smaller. We cannot judge of the senses of animals which breathe water – which separate air from water by their gills; but it seems probable, that as the quality of the water is connected with their life and health, they must be exquisitely sensible to changes in water, and must have similar relations to it, that an animal with the most delicate nasal organs has to air. – Sir H. Davy.
