Effects of size and nitrite exposure on respiration, oxygen partitioning, and growth of obligate air-breathing fish Channa striata

The effects of fish size and nitrite level on metabolic rate and growth were investigated in the obligate air-breathing snakehead Channa striata, which is an important aquaculture species in Vietnam. Channa striata displayed respiratory size dependence, whereby the standard metabolic rate (SMR) and routine metabolic rate (RMR) decreased progressively in an exponential manner as fish size increased from 50 to 200 g. A mildly elevated nitrite level of 5% of the LC50 96 h (12 mg NO2-/L or safe concentration) induced significant increases in Channa striata SMR and RMR, which were almost double that of the control at the same size. At mild elevation, nitrite caused no significant effect on fish growth and survival during 3 months of rearing. However, both growth and survival rates of fish reared at severely elevated nitrite levels were significantly lower than those of the control; in particular, survival rates were under 50%. While changes in size reduced SMR and RMR, the percentage of air oxygen partitioning remained unchanged. Channa striata upregulation of SMR and RMR and air-breathing regulation were not significantly proven in this study. In summary, maintaining water environments at levels lower than 12 mg NO2-/L with ample oxygenation will not affect the growth and survival rate of snakeheads.

Automated summary

The study showed that the metabolic rate and growth of the snakehead fish were affected by both fish size and nitrite levels. Mildly elevated nitrite levels significantly increased the metabolic rate of the fish, while severely elevated levels led to decreased growth and survival rates. Maintaining water environments with nitrite levels lower than 12 mg NO2-/L and sufficient oxygenation will not impact the growth and survival of snakeheads.