heavily laden with fat globules than is the white 

 muscle, suggesting- that lipids are the primary 

 source of energy in the red muscle. He also 

 showed that mitochondria were very abundant 

 in both the red and white muscle but more 

 abundant in the red. Nagayama (1961) studied 

 changes of some glycolytic intermediates to ob- 

 serve the phenomenon of browning in fish flesh. 

 He reported that glucose-6-phosphate, fructose- 

 6-phosphate, and fructose diphosphate pro- 

 duced browning but glucose-1-phosphate, AMP, 

 and ATP did not. The browning reaction was 

 said to occur through the loss of phosphate 

 whose ion later catalyzed the freed sugars re- 

 action with some amino group. In another 

 series of papers, Nagayama suggested that hex- 

 ose sugars were the limiting factors in brown- 

 ing of fresh fish but pentose sugars (ribose in 

 particular) were later liberated during storage 

 and contribute to browning. 



Crawford et al (1970) simulated stress in 

 skipjack tuna and compared some of the sugars 

 in the white muscle of this fish to those of un- 

 stressed fish. Sugars in stressed and unstressed 

 skipjack held at various temperatures were also 

 compared, as were organoleptic qualities of the 

 fish after processing and canning. It was con- 

 cluded that there were differences in some of 

 the chemical and organoleptic parameters mea- 

 sured; while there were some trends noted, 

 there was no overwhelming evidence connecting 

 the induced variables with the difference in 

 quality of the final product. It was reasoned 

 that such a complex experiment should be per- 

 formed more than once if one is to draw any 

 valid conclusions. The following study repeats 

 the experiment of Crawford et al. (1970) with 

 some added design features and measurements. 



It is not the purpose of this study to eluci- 

 date the mechanism of the Embden-Meyerhof 

 pathway in skipjack tuna although some com- 

 ments will be made. Rather, this study will 

 focus its attention on those conditions of stress, 

 time, temperature as they affect the rate at 

 which glycolysis proceeds and consequently the 

 final level of sugars formed in the fish muscle. 

 A wide range of temperatures was employed 

 to see if glycolysis can be retarded or increased 

 postmortem thus exercising some control over 

 the degradation of products formed. 



Live skipjack tuna were captured off the 

 shores of Oahu and were placed in shoreside 



tanks. They were observed for a day or two to 

 note their apparent health. Rested fish and ex- 

 ercised fish (induced stress) which served as 

 controls were sacrificed and canned immediate- 

 ly while others were sacrificed and held in sea- 

 water at 78°, 60°, and 32° F for time intervals 

 of 6 and/or 9 hr before canning. Some fish 

 were also frozen after holding to note the ef- 

 fect of freezing. Additionally, some fish were 

 frozen alive in 0° F refrigerated seawater (a 

 condition which often occurs on a commercial 

 tuna boat) and subsequently canned. A sam- 

 ple wedge for analyses of some autolytic degra- 

 dation products was taken from all fish before 

 canning. The organoleptic quality and some 

 chemical analyses were determined on the 

 canned products. 



MATERIALS AND METHODS 

 Materials 



The skipjack used in this experiment were 

 caught by the Bureau of Commercial Fisheries 

 MV Charles H. Gilbert off Honolulu, Hawaii, 

 using live bait and barbless hooks. The fish 

 were taken to Kewalo Basin and held alive in 

 special tanks developed by the BCF Biological 

 Laboratory (Honolulu). Only apparently 

 healthy fish were used after 1 or 2 days of ob- 

 servation. 



The 125 skipjack used in this experiment 

 were utilized as follows: 



A. 32° F study. 



1. Sacrificed (blow on the head) 5 "rest- 



ed" fish, sampled for chemical anal- 

 ysis and canned immediately (rest- 

 ed controls). 



2. Sacrificed 5 "exercised" fish (induced 



stress by chasing fish at the limit of 

 his swimming speed around a tank 

 for about 45 min at which time 

 signs of exhaustion appeared, e.g., 

 slowed swimming speed and/or 

 turning belly side up). These fish 

 were sampled for chemical analysis 

 and canned immediately (stressed 

 controls) . 



3. Sacrificed 10 rested and 10 stressed 



fish and held for 6 hr in 32° F circu- 

 lating seawater. Sampled and 



13 



