Effects of carbaryl and methyl parathion on bimodal respiration in tadpoles of Rana tigrina (Daud) (common frog)

Sublethal effects of carbaryl (CA) and methyl parathion (MP) on bimodal pattern of respiration were studied in Rana tigrina tadpoles as a function of developmental stages. The rate of aquatic respiration of tadpoles was decreased with an increase in stage from I to IV in the control and pesticide exposed tadpoleshowever, the aerial respiration showed the reversed trend and it indicates the shifting of the mode of respiration from aquatic to aerial during the development of tadpoles. CA caused a decline of aquatic respiration in IV stage while MP decreased the aquatic respiration from II stage onwards and it may be due to avoidance and to minimize the gill damage by pesticide contaminated water. The results obtained for total respiration were similar to those of aquatic respiration. A stage dependent change in the percentage of aerial/aquatic respiration was observed in control and pesticide exposed tadpoles. For instance, the aquatic respiration of control tadpoles was 96.2% in I stage and it gradually reduced to 93.8%, 82.6% and 67.8% in II, III and IV stages respectively. The aerial respiration showed the opposite trend in all the experimental tadpoles. The highest concentration of MP reduced the aerial respiration by 8% compared to control tadpoles in II stage and this reduction was 17 and 16% in III and IV stages respectively. Similar trend was also obtained in tadpoles exposed to CA but the level of reduction of aerial respiration was less than those exposed to MP. This suggests that, MP is more toxic than CA and shifting of respiration from aquatic to aerial was quick due to the pesticide stress