Observations made of the effect of noise upon perch, flounders, rock cod and dog-fish, using an electrically driven sound producer submerged in the water showed little observable reaction except in the case of perch, which avoided noise and gathered at the opposite end of their tank. With feeding associated with sound, the perch developed quickly a well-marked conditioned response, increasing in intensity on repetition, and resembling the trace conditioned reflex of mammals. The perch used in these feeding experiments also developed a strong visual conditioned reflex, being attracted to the surface by agitation of the water. It was possible to develop a very temporary protective response in these fish, by combining stimuli of darkness and sound.