Cooked muscle tissue of five fish species were observed by optical and scanning electron micrography. Species with firm texture had thin muscle fibers with considerable heat-coagulating material between them; species having soft texture had thick muscle fibers with little heatcoagulating material. When the cooked muscles were compressed by a Texturomcter, muscle fibers of the species having firm texture slid or shifted over one another to a lesser extent than those of species with soft texture. The heat-coagulating material seemed to obstruct the disolacement of the fibers. The diameter and mobilitv of muscle fibers are determinative of firmness of fish muscle tissue:

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The changes in viscoelasticity of natural actomyosin and myosin during thermal gelation were investigated by dynamic viscoelasticity measurements. Thermal gelation of natural actomyosin could be divided into four characteristic temperature ranges. The storage modulus increased considerably in the 32-43"C range, decreased sharply in the 43-52°C range, and then increased again in the .52-80°C range. For the thermal gelation of myosin, the storage modulus increased in two steps at two temperature ranges, i.e., 30-41"C and 51-80°C. An increase in the loss modulus was observed at an early stage of each of the two ranges.