Observations on Post mortem Biochemical Changes in Fish Muscle in Relation to Rigor mortis

Abstract

The influence of the degree of exhaustion of fish at death and their subsequent storage temperature on the relationship between rigor mortis, lactic acid formation and changes in certain acid-soluble phosphorus-containing fractions in muscle have been examined. The fish used were rainbow trout (Salmo gairdneri) and starry flounders (Platichthys stellatus) killed under controlled conditions in an aquarium and sockeye salmon (Oncorhynchus nerka) caught by gill net or seine net under commercial conditions. The majority of the fish contained little or no molybdate-labile P (phosphocreatine) at death, but in those that did (chiefly unexercised fish) the P of this fraction, sometimes after a short period of increase post mortem, decreased to a very low value. Acid-labile P (adenosine-triphosphate) decreased later post mortem than did phosphocreatine, and rigor developed during this period of decrease. Onset of rigor was detected at. higher concentrations of acid-labile P at 20 than at 0 °C. Acid-stable P decreased post mortem, but without showing the rather sudden disappearance from the muscle exhibited by the two labile fractions, the decrease continuing throughout rigor.In unexercised fish the relationship between the course of rigor and lactic acid formation was distinctly different at 0 and 20 °C. At 20 °C the lactic acid concentration reached a maximum in the muscle by the time rigor was fully established or very soon thereafter. At 0 °C accumulation was much slower and had only reached about 50% of its maximum concentration when rigor was fully established. Evidence was presented that the duration of full rigor is related to the continued production of lactic acid in the muscle, rather than to the quantity of lactic acid accumulated.