Student: Malthe Tvind Hvas
Timing: September 2014-September 2015
Status: ongoing

An investigation of the combined effects of hypercapnia and Nitrite on the Striped catfish (Pangasianodon hypophthalmus). In striped catfish, elevated CO2 causes a respiratory acidosis where blood pH is recovered within 24-48 hours by accumulation of HCO3-, which is counterbalanced by a decrease in Cl-. Elevated nitrite levels can occasionally occur in aquaculture systems, entering fish by competing with Cl- for anion uptake at the same branchial Cl-/HCO3- exchanger utilized in nitrite uptake. In the blood, nitrite oxidises the haem iron forming methaemoglobin, which cannot bind oxygen. Since striped catfish need to retain HCO3- to protect pH during hypercapnia, we hypothesized that elevated CO2 would protect against nitrite toxicity through a decreased activity of the Cl-/HCO3- exchanger. This was investigated in fish cannulated in the dorsal aorta allowing for repeated blood sampling for plasma ion and metheamoglobin measurements during combined and isolated exposures to 0.9 mM nitrite and 3% hypercapnia.