Hypoxanthine in Iced Freshwater Fish

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Abstract
The formation of hypoxanthine in ordinary muscle was followed in 36 individual yellow walleye (Stizostedion vitreum) and in 22 individual whitefish (Coregonus clupeaformis) stored in ice. At the time of death, the average hypoxanthine content was approximately the same for the two species (0.25 μmole/g); it increased gradually to 1.52 μmole/g in 22 days and to 2.54 μmole/g in 18 days in yellow walleye and in whitefish respectively. The average rate of formation in yellow walleye (0.06 μmole/g per day) was the same as in ordinary muscle of swordfish; the rate of formation in whitefish (0.13 μmole/g per day) was slightly higher than that of Atlantic salmon, but lower than that of haddock, petrale sole, and several other marine species. Large variation in rate of formation was noticed between individual yellow walleyes. The average hypoxanthine content of both yellow walleyes and whitefish taken as groups was found to be proportional to the number of days in storage. No difference in average rate of formation was noticed between whitefish fillets from opposite sides of the fish, nor between fresh and thawed fish. The hypoxanthine content appears to be suitable as an index of freshness for groups of fish, not of individual fish.