Swimming pattern in intact and decerebrated stingrays.

Stingrays swim with a rostral-to-caudal wave of elevation and depression of the enlarged pectoral fins. The present study compares the timing relations of swimming before and after decerebration in the same animals using electromyograms (EMGs). EMGs were recorded from several freely swimming, intact animals. Most recordings, however, were from stingrays suspended by vertebral clamps. Activity recorded from restrained animals exhibited the same timing relations as freely swimming animals. Therefore, the restrained preparation was used to compare locomotor rhythm in intact and decerebrate stingrays. The delay from the onset of activity recorded at a rostral segment to the onset of activity at successively caudal recording sites (intersegmental delay) was linearly related to the extent of the segmental separation. This relation was not changed by decerebration. Both the intersegmental delay and the EMG burst duration were linearly related to the period of the swim cycle. The intercepts for both relations fell around the origin. Therefore, stingray swimming demonstrates constant phase coupling. Neither the slopes nor the intercepts of the coupling relations were altered by decerebration. Histological examination of the fins indicates that at least two types of muscles exist. Superficial muscle is activated during slow swimming, while the deeper muscle is recruited during faster swimming.