Date of Award

1999

Degree Type

Thesis

Degree Name

Bachelor of Sciences Honours

Faculty

Faculty of Communications, Health and Science

First Advisor

Dr Annette Patak

Abstract

In order to grow, crustaceans must shed their exoskeleton in a process known as "moulting'. Although this process is short and intermittent, it remains dominant over the life of a crustacean. Physiological changes in the period between moults (intermoult) are comparatively quiescent as opposed to the periods directly before and after the actual moult, known as premoult, and postmoult respectively (West, 1997). Moulting is associated with distinct physiological changes including the breakdown of muscle (Musgrove and Geddes, 1985). This muscle breakdown, known as atrophy is the diminution in size of the actual muscle mass and is very specific, occurring to facilitate the withdrawal of the large pinnate claw muscle mass from the narrow basiischial joint (Mykles and Skinner, 1985). It is likely that atrophy does not occur in the abdomen as it is withdrawn through an opening similar in size to the actual muscle mass. This study aimed to determine and compare the effects of moulting on the characteristics of atrophic claw and non-atrophic abdominal muscles in the yabby, Cherax albidus. Although the moult cycle is a continuum, it may be sub-divided into several stages and sub-stages by reference to morphological changes in the integument state, and in development of the uropod setae using light microscopy. Three individuals of the yabby species Cherax albidus, were sacrificed at each of the following four stages, including intermoult (C1 - C2) early premoult (D1 to D1.3), late premoult (D2 – D4) and postmoult A. Claw and abdominal muscle were sectioned in a croystat at -20° C, and stained using three histochemical techniques; mATPase indicative of contractile speed; NADH-TR indicative of fatigue resistance and H&E, which visualizes structural characteristics. In this study, the mATPase and NADH-TR stains were developed for the yabby, Cherax albidus. Subsequently, several important cellular characteristics were determined for both claw and abdominal muscle over the moult cycle, including gross morphology, cellular morphology, fibre diameter, and fibre type distribution, at the four aforementioned strategic stages. In terms of these characteristics, the results suggest that abdominal muscles of the yabby Cherax albidus do not undergo moult-induced atrophy as opposed to the claw, consistent with the hypothesis, however both do exhibit characteristics of growth at postmoult. The main mechanisms of atrophy appeared be associated with mitochondrial aggregates, the proliferation of phagocytcs in fibres, and enlarged intermyofibrillar spaces. These indicators and mechanisms of atrophy were most evident at late premoult. Further studies are required to establish the exact association between these characteristics in claw muscle atrophy, and the underlying mechanisms. At postmoult, the muscle was restored firstly in the proximal region as it resembled the intermoult condition, whilst the distal region remained moderately affected by atrophy, and/or growth. In contrast to claw muscle, the abdominal muscle mass did not exhibit reductions in fibre diameter, or fibre type distributions, however did exhibit slight changes in cellular morphology. The extent of these changes suggest they were associated with growth rather than atrophy. Growth was exhibited as fibre splitting and was observed in both claw and abdominal muscle predominantly at the late premoult and postmoult stages. Five types of fibre splitting were observed, most of which were common to both muscles. The differing extents of particular types of fibre splitting between the claw and abdominal muscles may be related to recovery from atrophy. Hence, great changes associated with moulting were observed in the claw muscle of the yabby, Cherax albidus, whilst abdominal muscle remained relatively unaffected.

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