Effects of captivity and exercise on the energetics of locomotion and muscle of Carcinus maenas (L.)

Abstract

The exercise performance, oxygen consumption, lactate production, and some characteristics of a leg muscle have been investigated in the green shore crab, Carcinus maenas (L.), in animals recently collected from the shore, after 2 to 3 wk of captivity and after 2 wk of captivity with daily exercise. Exercise performance, as judged by the time to fatigue at a constant speed, declined in the captive quiescent group compared with recently collected animals, but was maintained in the captive but exercised group. Captive and captive-exercised animals showed reduced spontaneous activity compared with the recently collected animals. During walking, aerobic scope (the difference between the active and resting rates of oxygen consumption) was reduced in the captive and captive-exercised groups. Net lactate accumulation after similar periods of walking at similar velocities was reduced in the captive and captive-exercised groups compared with the recently collected animals and the anaerobic contribution to the calculated aerobic ATP production during walking declined from 60% in recently collected animals to 19–22% in captive and captive-exercised animals. The muscle fibres in the carpopodite extensor muscle showed a loss of mitochondria with captivity but a reduced loss in animals exercised in captivity; there was a reduction in cytochrome oxidase and citrate synthetase activities with captivity without exercise but hexokinase and phosphofructokinase activities were not affected by captivity with or without exercise. Captivity over 2 to 3 wk, without exercise results in a loss of aerobic and anaerobic capacity in the locomotor muscles producing reduced walking performance; this is perhaps related to the loss of the normal levels of activity of the animals in the sea. Daily exercise to some extent ameliorates this loss of metabolic capacity.