J. exp. Biol. 127, 427-442 (1987) 427 Itfnnted in Great Britain © The Company of Biologists Limited 1987 INTERNAL HYPOXIA-HYPERCAPNIA IN TENCH EXPOSED TO ALUMINIUM IN ACID WATER: EFFECTS ON BLOOD GAS TRANSPORT, ACID-BASE STATUS AND ELECTROLYTE COMPOSITION IN ARTERIAL BLOOD BY FRANK B. JENSEN AND ROY E. WEBER Institute of Biology, Odense University, Campusvej 55, DK-5230 Odense M, Denmark Accepted 5 September 1986 SUMMARY Tench exposed for 6 days to acid (pH5) hard water ([Ca z+ ] = S-Smmoll" 1 ) in the presence of aluminium (2mgl~') showed a rapid decrease (within 3 h) in dorsal aortic Po 2 and a simultaneous rise in Pco 2 - Arterial oxygen content and haemoglobin- oxygen (Hb-O2) saturation decreased sharply, as did red cell [Hb], whereas blood haematocrit (Hct) and [Hb] increased. Red cell nucleoside triphosphate (NTP) content was reduced within 1 day through a selective reduction in guanosine triphosphate (GTP). Although the rising Pco 2 caused an extracellular acidosis (to which lactic acid pro- duction and perhaps H + influx at the gills contributed), red cell pH increased compared to control values, mainly as a result of the decrease in Hb-C>2 saturation. Plasma [Cl~] declined, whereas [HCO3], [K + ] and [Ca 2+ ] increased. Ionic disturbances, however, were small compared to the changes in blood O2 transport, which appeared to correlate with high ambient [Ca 2+ ]. Tench exhibited a high tolerance to the acid-Al exposure and most of the above parameters showed partial recovery within 1—2 days. In some specimens, however, the exposure was lethal because of an obstruction of gill function, and arterial blood became almost completely deoxygenated and showed very low pH values and high lactate concentrations, attesting to deep internal hypoxia. INTRODUCTION Anthropogenic emission of industrial waste gases, such as sulphur dioxide (which is oxidized to sulphuric acid in the atmosphere), has increased the acidity of rain and led to an extensive environmental acidification of freshwater systems. The massive numbers of dead fish occasionally observed in such waters call for research elucidating the mechanisms and nature of physiological disturbances in acid-exposed fish. Teleost fish exposed to acid water below pH 5 generally show extensive losses of body electrolytes and disturbances in the acid-base balance (Ultsch, Ott & Heisler, 1981; McDonald & Wood, 1981; Hobe, Wood & McMahon, 1984). The severity of Key words: acid-base status, red cell pH, oxygen transport, aluminium, acid water.