it may be considered a short-cut method by which the embryo obtains energy 

 while awaiting the development of other glycolytic and tricarboxylic acid 

 cycle enzymes (Krahl 1956). The existence and relative importance of this 

 pathway in fish has yet to be investigated. A compound formed by the 

 hexosemonophosphate pathway, ribose, is liberated from various ribose- 

 containing compounds by enzymes present in muscle tissue of fish. 



Tarr (1952, 1953, and 195U) and Tarr and Bissett (195h) found that 

 ribose was cleaved from ribonucleic acid, ATP, ribonucleosides, ribonucleo- 

 tides, and ribose-5-phosphate added to the muscle of certain fish. More 

 recently, using lingcod muscle, Tarr (1955) was able to ourify a nonphos- 

 phorolytic nucleosidase capable of hydrolyzing ribonucleosides, such as 

 adenosine, inosine, guanosine, xanthosine, and cytidine. It appears that 

 fish muscle contains a ribonuclease and other enzymes that hydrolyze 

 ribonucleic acid to constituent mononucleosides. These, in turn, may be 

 attacked by a non-phosphorolytic riboside hydrolase enzyme, with the liber- 

 ation of ribose and a base. This degradation orocess appears to be more 

 rapid in fish than in warm-blooded animals (Hamoir 1955 b). 



Alcohol dehydrogenase, which in mammals is found almost exclusively 

 in the liver, has been isolated and purified from fish liver (Boeri et al. 



195U). 



ATP is the key compound for trapping the energy released during 

 carbohydrate oxidation in all forms of life and serves as the immediate 

 source of energy for muscular contraction. It therefore is not surprising 

 that considerable interest has been shown the presence and utilization 

 of ATP in fish. Contraction and rigor mortis in fish muscle have been 

 related to post-mortem changes in amounts of glycogen, ATP, and free sulf- 

 hydryl groups (Noguchi and Yamomoto 1955 a,bj Partmann 1953) • These 

 compounds decrease rapidly, reaching a minimum after 9 hours with full 

 rigor and a decrease in pH. Somewhat similar studies of fish muscle were 

 made by Fujimaki and Kojo (1953 a,b), in which glycogen, lactic acid, 

 ammonia, amide nitrogen, and pH were determined in frigate mackerel killed 

 by various methods. Fish that were left to die underwent a rapid decrease 

 of ATP, with a corresponding increase of adenylic acid and inosinic acid 

 within h hours. Reay and Shewan (19U9) have also reviewed the immediate 

 post-mortem changes in glycogen and lactic acid content and pH of fish 

 muscle. Compared to mammalian muscle, fish muscle usually contained less 

 glycogen, owing to exhaustion before death, and had a higher pHj these 

 factors increase the speed of onset of rigor mortis. 



Saito and Hidaka (1955 a,b$ 1956 a,b), using purified myosin frac- 

 tions isolated from carp muscle, have studied ATP-ase activity and stab- 

 ility and the post-mortem changes of myosin fraction nitrogen, ATP, and 

 free sulfhydryl groups in carp muscle. In general, ATP-ase activity of 

 the myosin fractions was high and showed a temperature optimum similar 

 to that of rabbit muscle. The decrease of this activity at 25° C. over 

 a period of 10 hours coincided with the decrease in sulfhydryl groups. 

 Rigor mortis also paralleled the decrease of ATP and sulfhydryl groups 

 and was complete after 6 hours, at which time all ATP had disappeared. 



