Some properties of the collagens of myocommata and skin from three species of fish are described. The musculature of hake separates readily into flakes because of intrinsic weakness in the connective tissue. The corresponding tissue of catfish is unusually strong and holds the musculature together under almost all conditions, while that of cod has properties intermediate between the other two. Skin is stronger than myocommata, thickness for thickness, but the order of strength between species is still hake < cod < catfish.The acid-soluble collagen of hake in citrate buffer has the highest thermal denaturation temperature of the three species (19.4" compared with 13.4" for catfish) and the highest content of imino acids. It also has the highest proportion of stable intra-molecular crosslinks.

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Gaping' is a phenomenon in which the connective tissues of fish fillets fail to hold the blocks of muscle together. Slits appear across the surface of the muscle which cannot then be mechanically skinned, or, in the case of smoked salmon fillets, sliced.Seasonal increases in the gaping of salmon fillets coincide with a fall in the postmortem pH of the flesh, occurring in June-July.Extensive gaping can be caused by fish entering rigor mortis at too high a temperature. In trout, this temperature is considerably higher than in gadoids, suggesting that gaping from high-temperature rigor may in practice be fairly rare in salmonids.The thermal denaturation temperature ( TD) of acid-soluble collagen isolated from the turbot farmed in warmed water does not differ significantly from that of the connective tissues of those reared at normal temperatures. This observation is discussed in relation to gaping.