Anaerobic Respiration in a Cyprinoid Fish Rasbora daniconius (Ham)

Abstract

ASPHYXIA, anoxia and hypoxia occur only when the ambient oxygen and carbon dioxide in water reach threshold level. Lethal or critical content of oxygen has been determined by various authors1–8 in many fishes, the time of anoxia being totally dependent on the composition of the surrounding water. In the present investigations one fish was introduced into a glass jar containing 2.6 l. of tap water; two such experiments were performed simultaneously. The initial concentration of oxygen in water, measured by Winkler's method, was 4 ml./l, and that of the free carbon dioxide, measured by titration with sodium hydroxide with phenothalein as indicators, was 22 mg/l. The pH of the water was 8.5. The fish in one experiment weighed 4.8 g. The jars were hermetically sealed and covered with cardboard on all sides. The fish was expected to die by suffocation as the oxygen concentration was continuously decreasing, but it survived well for 81 days. During this period the temperature of the water varied between 29° C and 33° C. The weight of the fish after death was only 1.08 g, thereby showing a marked reduction by 3.72 g. The concentration of oxygen in water after the death of the fish was found to be nil while that of carbon dioxide was 39 mg/l. The pH was 9.9. In the other experiment in similar conditions the fish survived for 102 days.