ABSTRACT
A nomogram is presented which allows the rapid assessment of acid-base status in brook trout (Salvelinus fontinalis Mitchill) at 18°C.
Due to a 
of 3·5–4·3 mmHg in the respirometer water, the fish from which data were obtained for determination of zero base excess values were suffering from slight respiratory acidosis. Trauma of surgery and anaesthetization as well as confinement in the respirometer might also have generated a slight metabolic acidosis.
Base excess values for trout with a chronically implanted dorsal aortic cannula ranged from −3 to + 3m-equiv/l. Blood buffer values of d[HCO3−]/dpH = 7·50±4·42 slykes and 
were found. Mean plasma protein concentration was 3·6± 0·8 g/100 ml plasma and the buffering power of plasma was approximately 40% that of whole blood. Plasma proteins are more important blood buffers in fish than in humans.
