EFFECTS OF ENDURANCE TRAINING IN THE LEOPARD SHARK, TRIAKIS-SEMIFASCIATA

This study is the first to examine the effects of endurance training i n an elasmobranch fish. Twenty-four leopard sharks (Triakis semifascia ta) were divided randomly into three groups. Eight sharks were killed immediately, eight were forced to swim continuously for 6 wk against a current of 35 cm s(-1) (60%-65% of maximal sustainable swimming speed ), and eight were held for 6 wk in a tank without induced current. The re were no changes due to training in maximal sustainable speed, oxyge n consumption rates, percentage of the myotome composed of red and whi te muscle fibers, blood oxygen-carrying capacity, liver mass, liver li pid, glycogen, and protein concentrations, white muscle protein conten t, heart ventricle mass, or the specific activities of the enzymes cit rate synthase, pyruvate kinase, and lactate dehydrogenase in the heart ventricle. In red myotomal muscle, citrate synthase activity increase d 17% as a result of training, but there was no change in muscle fiber diameter. The greatest effects occurred in white myotomal muscle, in which a 34% increase in fiber diameter and a 36% increase in the activ ities of citrate synthase and lactate dehydrogenase occurred as a resu lt of training. The conditioned fish also had significantly higher gro wth rates. The observed effects within the myotomal muscle may reflect the higher growth rates of the trained leopard sharks, or they may be a specific response to the increased energetic demands of the trainin g activity, indicating characteristics that limit swimming performance in leopard sharks.