ELEVATED LEVELS OF ARGININE VASOTOCIN IN THE BRAIN OF BROOK TROUT (SALVELINUS-FONTINALIS) FROM ACID LAKES - A FIELD-TEST OF A POTENTIAL BIOMARKER FOR ACID STRESS

The levels of arginine vasotocin (AVT), an osmoregulatory peptide, wer e determined by radioimmunoassay in brain tissue of brook trout (Salve linus fontinalis) of a wide size range (50-380 mm) from softwater Laur entian lakes ranging in pH from 5.0 to 6.9 at different seasons. Multi variate models (ANCOVA) were developed to quantify the relationship be tween AVT, pH, body size, and season. Brain AVT levels increased with body size, and the allometric slope was highest in the low-pH lakes (p H 5.0-5.5). Although brook trout >150 mm had higher brain AVT levels a t low pH, no significant differences were detected for brook trout <15 0 mm. We hypothesize that the sensitivity of brook trout at the parr s tage to acid stress may be linked to their inability to mobilize a hor monal response involving AVT. The seasonal variation in brain AVT leve ls was similar in all the lakes studied, summer levels being the highe st. Although this field study revealed that AVT levels depend also on factors other than acid stress (body size and season), our ANCOVA mode ls allow adjustment for the effects of these covariables. Analyses of this type can be used to field test and calibrate biomarkers for use i n ecotoxicology.