SEASONAL EFFECTS OF BLEACHED KRAFT MILL EFFLUENT ON REPRODUCTIVE PARAMETERS OF WHITE SUCKER (CATOSTOMUS-COMMERSONI) POPULATIONS OF THE ST-MAURICE RIVER, QUEBEC, CANADA

Reproductive parameters and accumulation of chlorophenolic compounds b y white sucker (Catostomus commersoni) populations exposed to bleached kraft mill effluent (BKME) were studied in the St. Maurice River, Que bec. Compared with unexposed populations from the same waterway, expos ed white sucker showed obvious effects of chemical exposure as far as 100 km downstream of the mill, as revealed by a strong induction of et hoxyresorufin O-deethylase (EROD) activity. In males, circulating plas ma testosterone levels were the same at all sites, while 11-ketotestos terone levels were significantly lower at exposed stations. In females , testosterone and 17beta-estradiol levels were significantly reduced at the two exposed stations relative to the reference station. Despite different hormone levels during sexual maturation, gonad weight as a proportion of carcass weight was similar at all sites for both sexes d uring early gonadal development. The relationship between carcass weig ht and fecundity was more variable at the station immediately downstre am of the mill. Biochemical and physiological parameters measured in t his study do not allow us to clearly relate perturbations in plasma st eroid levels to impaired reproduction as measured by gonad weight and fecundity.