Anderson, John Richard2012-08-30b12773347http://hdl.handle.net/1885/9226On the basis of the work of Blazka (1958, 1960) the fish Carassius carassius (L.) has been described as a "true facultative anaerobe", capable of surviving 5months of anoxia at low temperatures. In this respect it is unique among vertebrates. However, a careful examination of Blazka's methods and results reveals that the general acceptance of his conclusions is quite unjustified. Additional work is required to establish the extent, nature and significance of the anaerobic resistance of c. carassius. In this thesis I have determined the anaerobic resistance of a closely related species of fish, Carassius auratus (L.)Under carefully defined and controlled experimental conditions, and I have sought the mechanisms responsible for its resistance. I found that: 1.c. auratus has a limited resistance to anoxia, that is to oxygen concentrations below 0.01 mg o2 1-1. Its resistance depended on acclimation temperature and season. The median resistance of c. auratus at 18°C was 7 hours in February, and 34 hours in November. At 5°C it was 11 hours in March and 75 hours in October. While the anaerobic resistance of c. auratus was found to be far less than that which Blazka (1958) claimed for c. carassius, it nevertheless represents a very prolonged anaerobic resistance'of a vertebrate, particularly since it was determined under very stringent experimental conditions. 2. At very low oxygen concentrations (0.1 - 0.2 mg o2 1-1), the oxygen consumption of c. auratus at 18°C was less than 1% of its consumption in aerated water, yet its resistance was twice that to anoxia (0.01 mg o2 1-1). 3. The oxygen in the swimbladder of c. auratus at 18°C and 5°C does not contribute significantly to its anaerobic resistance. 4. The effect of anoxia on the total metabolic rate of c. auratus was assessed by determining its heat production before, during and after anoxia. During anoxia the metabolic rate was reduced by 80% at 18°C and 70% at 5°C.The metabolic rate declined rapidly in association with the reduction in oxygen concentration and reached minimum levels soon after the onset of anoxia. It remained relatively constant throughout 9 hours and 20 hours anoxia at 18°C and 5°C respectively. When oxygen was reintroduced following the period of anoxia, the metabolic rate returned rapidly to the pre-anoxic levels. The decline in the total metabolic rate of c. auratus during anoxia was partially attributed to a reduction in its physical and ventilatory activities. 5. During aerobic recovery from anoxia, the oxygen consumption of c. auratus was significantly elevated above its pre-anoxic level for more than 12 hours and 16 hours at 18°C and 5°C respectively. The significance of this excess oxygen consumption was discussed in relation to the-current standing of the concept of an oxygen debt in -mammals and fish. It was concluded that the demonstration of anexcess oxygen consumption during recovery of c. auratus from a period of anoxia, is in itself insufficient to establish the nature of the anaerobic metabolism, or indeed, whether or not an oxygen debt is incurred or repaid. 6. A significant increase in lactate concentration was found in liver tissue at 18°C, and in liver, red and white muscle tissues and brain at 5°C, after 8 hours and 15 hours anoxia respectively. The amounts which accumulated were small in relation to the length of the anoxic periods. 7. The ATP concentrations, the ATP/ADP ratio and the adenylate energy charge of liver• tissue declined during anoxia at both 18°C and 5°C. At 18°C the ATP/ADP ratio declined by 90% and the adenylate energy charge fell from 0.59 to 0.23 after 8 hours anoxia. At 5°C the ATP/ADP ratio declined by 80% and the adenylate energy charge fell from 0.78 to 0.43 after 15 hours anoxia. The ATP/ADP ratio and the adenylate energy charge of the brain was maintained during anoxia at 5°C. It was postulated that the reduction in metabolic rate of c. auratus during anoxia could occur as a passive consequence of the changes in the concentrations of the adenylates and in the adenylate energy charge in most of the tissues, or alternatively as a reflex response to the decline in oxygen concentration. Further work is required to establish the nature of the anaerobic metabolism of c. auratus, the mechanisms responsible for the decline in its metabolic rate and the adaptations which enable the tissues to withstand a reduction in their energy expenditures and ATP levels for long periods. It was concluded that c. auratus has a limited resistance to anoxia, which depends upon its capacity to incur and sustain a substantial reduction in its total metabolic rate, and to withstand a reduction in the ATP concentrations and adenylate energy charge in most of its tissues. In this respect the mechanisms responsible for the anaerobic resistance of c. auratus are similar to those of other vertebrates, but dissimilar to the mechanisms responsible for the anaerobic tolerance of the "true facultative anaerobes".en-AU197510.25911/5d78dba2001a2