Introduction

Crustaceans represent a group of animals which grow intermittently throughout juvenile and adult life. Development involves a series of larval stages before metamorphosing into the young juvenile. In the adult, growth is centred around ecdysis when the old exoskeleton is lost and the new exoskeleton expands by a subsequent increase in size. The number of moults can depend on many factors, both environmental and intraspecific with up to 12 moults in the first year of life. Increments in crabs can vary by 3–44% of the original carapace width (Hartnoll, 1982) with growth completed over 2–7 days. In some cases growth can be biphasic, for example, in the isopod, Idotea rescata, with the posterior half of the animal shedding prior to the anterior half. In the edible crab, Cancer pagurus, it takes up to 15–20 years for an adult male to reach maximal size (Bennet, 1974) whereas the common green shore crab, Carcinus maenas, takes only 4 years (Crothers, 1967).

Tissue growth has been shown to occur in cycle with increasing body size; the predominant growth phase occurring during the pre- and post-moult phases. This is also true for the major muscle groups such as the abdominal and leg muscles (El Haj, Govind & Houlihan, 1984). Crustacean muscle is similar in structure to vertebrate and mammalian skeletal muscle with muscle proteins assembled into sarcomeric units aligned along a fibre. Muscles are composed of large fibres arranged in a pennate fashion around a central apodeme.