Respiratory and acid-base pathophysiology of hydrogen peroxide in rainbow trout ( Oncorhynchus mykiss Walbaum)

Abstract

Rainbow trout were exposed for 20 min to 100 or 500 mg L −1 hydrogen peroxide. Dorsal aortic blood samples were withdrawn prior to, at 0, 1, 3, 6 and 24 h post-exposure, and blood gas tensions ( Pa O 2and Pa CO 2), blood gas content ( CaO 2and CaCO 2), haematocrit, [haemoglobin], [methaemoglobin], pH (pH e) and plasma catecholamines were measured. Gills from a second group of fish exposed to 500 mg L −1 H 2O 2 were fixed in 10% neutral buffered formalin for histological examination. Pa O 2and Pa CO 2 increased significantly during exposure but rapidly decreased after withdrawal of hydrogen peroxide. Blood pH decreased and haematoctrit, [haemoglobin] and [methaemoglobin] and plasma catecholamine levels were were all significantly elevated following exposure to 500 mg L −1 but not 100 mg L −1 or controls. A reduction in the amount of O 2 specifically bound to haemoglobin was indicative of an acute hypoxemia which was recovered to control levels by 6 h post-exposure in survivors. There was swelling and intercellular edema in the gill lamellae of those fish exposed to 500 mg L −1 hydrogen peroxide. It is concluded that hydrogen peroxide exposure elicited an acute stress response and impaired oxygen transport due to a combination of increased haematocrit, reduced oxygen carrying capacity perhaps in part due to the respiratory acidosis and oxidation of haemoglobin.