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

摘要

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 fertilized chinook salmon (Oncorhynchus tshawytscha) eggs. The ATP levels of unfertilized chinook salmon eggs were 2.61 +- 0.14 nmol ATP per egg (17.6 +- 0.9 #mu#moll~-1 relative to cell water) and ranged from 1.98 to 3.63 nmol ATP per egg. The ATP content of unfertilized eggs maintained at 10 deg 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 deg C (in an effort to speed egg metabolism and ATP turnover) resulted in significant O_2-independent decreases in ATP levels. However, ATP levels of unfertilized eggs exposed to 1 nmoll~-1 potassium cyanide (a potent inhibitor of oxidative phosphorylation) at 10 deg C were significanly decreased after 24 h and continued to decline throughout the 120 h maintenance period to about 30% of time= 0 values. Maintenance with exogenous nutrients (5 mmoll~-1 acetate plus 5 mmoll~-1 pyruvate) over 120 h at 10 deg C did not alter the ATP content of unfertilized eggs. Eggs activated by exposing them to 10 deg C water for a few minutes showed a rapid decrease in ATP values, regardless of whether the eggs were fertilized or not. Following an initial alpha 25% drop after fertilization, the ATP levels remained stable for the remainder (5 d) of the incubation period in eggs maintained in 10 deg C water. Therefore, unfertilized chinook salmon egg ATP levels appear to be relatively stable and maintained by a low, cyanide-inhibitable metabolism. The stability of egg ATP levels may be one reason that salmonid eggs can be stored for several days while eggs from other fishes cannot.