Free ribose, /xM/g. — The free ribose content 

 varied from 0.5 to 1.4 fj-M/g in the raw muscle. 

 The level in the fish held at higher temperatures 

 tended to be slightly higher than the content of 

 the fish held in 32° F SW. This small rise may 

 be attributed to the breakdown of purine com- 

 pounds. 



The free ribose content of the canned fish 

 was not significantly different from that of the 

 raw muscle. Since ribose readily participates 

 in browning reactions, this may seem surpris- 

 ing. However, it may be that such small 

 amount of ribose cannot effectively compete 

 with the much larger amounts of glucose and 

 glucose phosphate in browning reactions. 



Pyruvate and lactate, yuM/g. — The pyruvate 

 content was very consistent. It varied from 

 0.07 to 0.20 /i-M/g previously reported by Craw- 

 ford et al. (1970) . The content of the canned 

 product was approximately the same. 



The lactate content varied from 109 to 170 

 ixu/g. These levels agree with the results re- 

 ported by Crawford et al. (1970). However, 

 Crawford also reported significantly lower lac- 

 tate content in the control whereas the content 

 of the controls in this experiment are not sig- 

 nificantly different from those of the fish held 

 for 6 or 9 hr in RSW or SW. The difference 

 may lie in the fact that in the earlier experi- 

 ment extracts were made immediately after 

 sampling, but in this experiment the extracts 

 were prepared after first freezing the sample 

 wedges in liquid nitrogen. 



There were no consistent differences in the 

 lactate content of the stressed and rested fish. 

 This may indicate that fatigue in the skipjack 

 is not due to lack of NAD but rather may be 

 due to the fish's inability to exchange oxygen 

 and carbon dioxide fast enough across its gills 

 (there was suflScient oxygen available in the 

 tank at all times) . There was a small decrease 

 in lactate content in the canned product. 



Purines and Purine Derivates (Table 3) 



Inosinemonophosphate, ixU/g. — The esti- 

 mated inosinemonophosphate (IMP) content 

 varied from 7.4 to 13.0 /uM/g. With one ex- 

 ception, the unfrozen rested controls showed a 



lower IMP content than the stressed controls. 

 However, the frozen rested and stressed con- 

 trols show about the same content. The IMP 

 content of the rested fish is higher than the 

 stressed fish when held in 32° F RSW whether 

 frozen or unfrozen. These results indicate that 

 the stressed fish began with higher levels of 

 high energy phosphorylated compounds but de- 

 graded to lower levels when held in 32° F RSW 

 as expected. On the other hand, the IMP con- 

 tent of the rested fish showed no significant 

 change when held at the same temperature 

 ( see total purines, Table 3 ) . The same changes 

 also occur in the fish held in 78° F SW for 6 hr, 

 but both rested and stressed fish show a de- 

 creased content when held. Also, the unfrozen 

 stressed fish has a higher IMP content than the 

 frozen. These obsei-vations may be attributed 

 to the generation of more enzymes for the syn- 

 thesis of high energy phosphorylated compound 

 to meet higher energy output during stress. 



It is interesting to note that the skipjack held 

 in 60° F RSW for 6 hr and in 78° F SW for 

 9 hr showed a higher IMP content than the fish 

 held at 32° F or 78° F for 6 hr. This indicates 

 that perhaps purines are being synthesized as 

 well as being degraded at these temperatures. 

 ( See inosine content and total purines. Table 2 ) . 

 This is in sharp contrast to the results reported 

 by Crawford et al. (1969) where IMP showed 

 a marked degradation with time in skipjack 

 (stressed) held for 30 hr at 30° F RSW. 



The IMP content of the can varied from 10.0 

 to 13.4 ixU/g and was fairly uniform for all 

 treatments. Another point of interest is that 

 the IMP content of the canned product of rested 

 and stressed fish held in 32° F RSW and 78° F 

 SW showed an increase whereas the fish in 

 other treatments which had higher IMP levels 

 before canning, show little change. 



The author hesitates to speculate about what 

 specific purine compound may have been syn- 

 thesized but will point out that ATP, ADP, and 

 AMP contents of fish are readily subject to 

 degradation, especially in the presence of heat. 



Inosine and hypoxanthine, /itM/g. — The ino- 

 sine (I) content (estimated), which results 

 from the degradation of IMP, varied from 0.3 

 to 4.7 jaM/g. In general, the I content increased 

 with time and temperature, as expected. The 

 contents of the can show a tendency to remain 



18 



