Effects of two different feeding regimes on the chela closer muscles of the shore crabCarcinus maenas(L)

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Abstract
Two groups of shore crabs in terminal anecdysis were fed for six months on either live winkles (hard feeders) or fish flesh (soft feeders) and the closer muscles of their chelae were then compared with respect to maximum stresses induced by nervous stimulation, sarcomere lengths, and muscle fibre diameters. Mean maximum stresses in major and minor chelae of hard feeders (785 and 537 kN m‐2 respectively) were significantly greater than those of soft feeders (603 and 438 kNm‐2). Mean sarcomere lengths in the closer muscles of half open major and minor chelae of hard feeders (14.1 and 9.0 μm respectively) were significantly longer than those of soft feeders (13.0 and 8.0 μm). Fibre diameters were greater in major than in minor chelae and in larger than in smaller crabs, but no correlation was found with feeding regime. Comparison with a group of freshly collected crabs showed no significant differences between these and the hard feeders. Thus the observed differences between hard and soft feeders consisted of an intermoult reduction in strength and in sarcomere length in the chela closer muscles of the latter, probably due to lack of exercise.