3.1. Microstructure
The photomicrographs of fresh water prawn and tiger prawn showed the arrangement of muscles in the form of bundles of muscle fibres (Fig. 1). The specimens of tiger prawn showed more compact arrangement of muscle tissue compared to those of freshwater prawn. The unirradiated control sample of both the species showed gaps between the bundles of muscle fibres; however, individual muscle fibres were not delineated. Irradiated specimens with doses up to 10 kGy showed no significant histological changes compared to that of the controls but at a higher dose of 20 kGy distinct gap between the muscle fibres became visible (pointed with arrows) which might be due to an increased compactness of the myofibrils within the muscle fibres. The observation is in conformity to Yoon (2003) who reported shrinkage in sarcomere width (myofibril diameter) in irradiated chicken meat at a lower dose of 2.9 kGy. Earlier, Anglemier, El-Badawi, and Cain (1964) had reported slight tightening of muscle structure at the sterilizing doses due to an increased number of weak hydrogen or electrostatic bonds.