Effect of exposure to sublethal concentrations of sodium cyanide on the carbohydrate metabolism of the Indian Major Carp Labeo rohita (Hamilton, 1822)

Experiments were designed to study in-vivo effects of sodium cyanide on biochemical endpoints in the freshwater fish Labeo rohita. Fish were exposed to two sublethal concentrations (0.106 and 0.064mg/L) for a period of 15 days. Levels of glycogen, pyruvate, lactate and the enzymatic activities of lactate dehydrogenase (LDH), succinate dehydrogenase (SDH), glucose-6-phosphate dehydrogenase (G6PDH), phosphorylase, alkaline phosphatase (ALP), acid phosphatase (AcP) were assessed in different tissues (liver, muscle and gills). Result indicated a steady decrease in glycogen, pyruvate, SDH, ALP and AcP activity with a concomitant increase in the lactate, phosphorylase, LDH and G6PD activity in all selected tissues. The alterations in all the above biochemical parameters were significantly (p<0.05) time and dose dependent. In all the above parameters, liver pointing out the intensity of cyanide intoxication compare to muscle and gills. Study revealed change in the metabolic energy by means of altered metabolic profile of the fish. Further, these observations indicated that even sublethal concentrations of sodium cyanide might not be fully devoid of deleterious influence on metabolism in L. rohita.

Blood acidification in the swimbladder: mechanisms and metabolic pathways

The metabolism of gas gland cells of the swimbladder epithelium is specialized for the production of acidic metabolites that are released into the blood stream and provoke an increase in gas partial pressure by reducing the effective gas-carrying capacity of the blood. In a subsequent step this initial increase in gas partial pressure is multiplied by back-diffusion of gas molecules from the venous to the arterial side in the countercurrent system, the rete mirabile. Thus, gas partial pressures of up to several hundred atmospheres can be generated in the swimbladder. Measurements of metabolic end products and analysis of the formation of 14C02 from [1-14(superscription) C] glucose and [6-14(superscription) C] glucose revealed that the acidic metabolises are lactic acid, produced in the glycolytic pathway, and also C02, formed in the pentose phosphate shunt. C02 easily enters the blood stream by diffusion. The release of protons from isolated gas gland cells, however, is highly dependent on the extracellular sodium concentration. This sodium dependence can in part be blocked by addition of amiloride, indicating that a Na+/ H+ exchanger is involved in the release of protons. A significant decrease in the rate of proton secretion in the presence of the carbonic anhydrase inhibitor ethoxzolamide indicates that the second major route for the release of protons includes carbonic anhydrase activity and the diffusion of C02.