MONITORING AQUATIC ENVIRONMENTS RECEIVING INDUSTRIAL EFFLUENTS USING SMALL FISH SPECIES-2 - COMPARISON BETWEEN RESPONSES OF TROUT-PERCH (PERCOPSIS OMISCOMAYCUS) AND WHITE SUCKER (CATOSTOMUS-COMMERSONI) DOWNSTREAM OF A PULP-MILL

To further evaluate the suitability of small fish species for sentinel monitoring, a comparison was made between the responses of trout-perc h (Percopsis omiscomaycus) and the larger white sucker (Catostomus com mersoni) under similar conditions of pulp mill effluent exposure and m obility. Fish were collected upstream and downstream of a thermomechan ical pulp mill on the Kapuskasing River, Ontario, Canada, where the pr esence of a hydro dam restricts the movement of fish between reference and exposure areas. Trout-perch collected downstream of the mill were shorter, lighter, and younger than upstream fish, whereas exposed whi te sucker were longer, heavier, and, for male sucker, older than refer ence fish. Only male trout-perch showed induced hepatic mixed function oxygenase activity (7-ethoxyresorufin-O-deethylase). Both forskolin-s timulated in vitro production of 17 beta-estradiol in trout-perch and plasma concentrations of 17 P-estradiol in sucker were significantly d epressed in exposed fish. The inconsistency in responses between speci es made it difficult to determine how the opposing responses were rela ted and which species was most sensitive to instream conditions. Despi te the discrepancies, use of an interpretation framework indicated tha t both species identified similar potential problems (e.g., size-selec tive mortality and recruitment problems), suggesting that either speci es could be used as a sentinel species at this site.