Adenosine triphosphate levels of chinook salmon (Oncorhynchus tshawytscha)eggs following in vitro maintenance and activation/fertilization

To further examine the concept of egg quality and the physiology of stored salmonid eggs, we investigated the effects of different oxygen tensions on the adenosine triphosphate (ATP) levels of unfertilized, activated, and fer tilized chinook salmon (Oncorhynchus tshawytscha) eggs. The ATP levels of u nfertilized chinook salmon eggs were 2.61 +/- 0.14 nmol ATP per egg (17.6 /- 0.9 mu mol l(-1) relative to cell water) and ranged from 1.98 to 3.63 nm ol ATP per egg. The ATP content of unfertilized eggs maintained at 10 degre es C under 100% O-2, 21% O-2, and 100% N-2 remained unaltered throughout a 120 h storage period. Storing eggs under identical conditions at 20 degrees C (in an effort to speed egg metabolism and ATP turnover) resulted in sign ificant O-2-independent decreases in ATP levels. However, ATP levels of unf ertilized eggs exposed to 1 mmol l(-1) potassium cyanide (a potent inhibito r of oxidative phosphorylation) at 10 degrees C were significantly decrease d after 24 h and continued to decline throughout the 120 h maintenance peri od to about 30% of time=0 values. Maintenance with exogenous nutrients (5 m mol l(-1) acetate plus 5 mmol l(-1) pyruvate) over 120 h at 10 degrees C di d not alter the ATP content of unfertilized eggs. Eggs activated by exposin g them to 10 degrees C water for a few minutes showed a rapid decrease in A TP values, regardless of whether the eggs were fertilized or not. Following an initial similar to 25% drop after fertilization, the ATP levels remaine d stable for the remainder (5 d) of the incubation period in eggs maintaine d in 10 degrees C water. Therefore, unfertilized chinook salmon egg ATP lev els appear to be relatively stable and maintained by a low, cyanide-inhibit able metabolism. The stability of egg ATP levels may be one reason that sal monid eggs can be stored for several days while eggs from other fishes cann ot.