Some auditory discrimination experiments on marine fish

The ability of cod, Gadus morhua (L.), and haddock, Melanogrammus aeglefinus (L.), to discriminate changes in sound direction and amplitude was studied using a cardiac conditioning technique. In one experiment it was found that the masking effect of noise transmitted from one sound projector on the ability of the fish to detect a tone (60–380 Hz) transmitted from another projector was reduced by 7 dB when the angle between the projectors was 45° or greater. It was also shown that the fish could be conditioned to a change in the direction of a pulsed tone switched between two projectors. The fish were able to discriminate changes in sound amplitude of 1·3–9·5 dB at frequencies between 50 and 380 Hz. The results are discussed in relation to sound localization in fish.