Effects of nitrite on respiration of basa catfish (Pangasius bocourti)

Abstract

This study was conducted to investigate effects of nitrite (NO2-) on respiration of basa catfish at 27˚C and 33˚C using bimodal intermittent-closed respirometry. The experiment 1 was conducted with separated groups of fish (20-40g) in different levels of NO2- (0; 0.09 mM; 0.22 mM; 0.44 mM) at 27˚C; the experiment 2 was conducted with separated groups of fish in different levels of NO2- (0 and 0.09 mM) at 33˚C. In the treatments with nitrite levels (0.09 mM; 0.22 mM; 0.44 mM), the oxygen consumption of individual fish of each treatment was measured for 20 hours in nitrite-free water (day 1), followed by 20 hours of nitrite exposure (day 2), finally the bacterial oxygen consumption (background) was measured for the next 2 hours without fish. At the experiment 2, fish was acclimated in composite tank (2 m3) at 33ºC for 1 week before setting into the chamber of respirometer and carry out was similar to experiment 1. Besides, oxygen consumption of fish in the control treatment was measured 40 hours in nitrite-free water. The results showed that there was no significant in average MO2 between the day 1 (220±12.9 mgO2/kg/h) and the day 2 (236±9.27 mgO2/kg/h) at control fish at 27oC. However, MO2 of fish exposed to nitrite were decreased at the day 2 compared with the day 1. MO2 of exposure fish decreased with the nitrite increase. The reduction of the treatment 0.44 mM was lowest and reached the values of 161±15.8 mgO2/kg/h. The variation of SMR and MO2max was similar to the variation of MO2. The difference of SMR and MO2max of the treatment 0.44 mM and control treatment was significant (p<0.05). The metabolic rate of 33oC treatment fish was significantly higher than that of the 27oC treatment fish. The metabolic rate of 33oC treatment fish was significantly higher than that of the 27oC treatment fish. In the control treatment, the SMR, MO2 and MO2max of 33oC treatment fish and the 27oC treatment fish were 336; 250; 448 and 220; 167; 306 mgO2/kg/h, respectively. The Q10 values for MO2, SMR and MAX were not too high, the values of 1.88; 1.66 and 1.87 between 27oC and 33oC, respectively, revealing low temperature sensitivity on this species.