Behavioral discrimination of water motions caused by moving objects

We tested whether goldfish, Carassius auratus, discriminate hydrodynamic st imuli caused by moving objects. Blindfolded goldfish responded to a passing object with changes in inter-gill-movement intervals. To learn whether gol dfish can discriminate water motions caused by different moving objects we habituated them to a certain object stimulus. If the stimulus was altered. e.g., by altering speed, direction of motion, or size or shape of the objec t, fish again showed a temporary suspension of breathing when the object pa ssed by. If animals failed to respond to an altered stimulus. we paired thi s stimulus with a weak electric shock during training. Goldfish discriminat ed object motion direction. In addition, in two choice experiments goldfish discriminated water motions caused by objects which moved with different s peeds (e.g.. 5 cm s(-1) versus 6 cm s(-1)), or by objects which differed in size (e.g.. 1 cm x 1 cm versus 1.4 cm x 1.4 cm cross section), or shape (e .g., a round versus a triangular object). If object size and;or shape was v aried quasi-randomly such that the faster moving object not always caused t he greatest water velocities, fish still discriminated object speed.