Reproductive Dysfunction and MFO Activity in Three Species of Fish Exposed to Bleached Kraft Mill Effluent at Jackfish Bay, Lake Superior

Abstract Our recent studies have demonstrated reproductive dysfunction in white sucker (Catostomus commersoni), longnose sucker (C. catostomus) and lake whitefish (Coregonus clupeaformis) populations exposed to bleached kraft mill effluent (BKME). Although all three species show elevated levels of hepatic mixed function oxygenase (MFO) activity and depressed circulating steroid levels, we have been unable to provide clear evidence of whether these two events are directly linked to whole organism changes. Although depressed steroid levels appear to be linked to delayed sexual maturity, changes in fecundity and reduced secondary sexual characteristics in white sucker and lake whitefish, longnose sucker show no impacts of reduced steroid levels on reproductive performance. Installation of secondary treatment at this pulp mill did not alleviate the steroidal dysfunction or MFO induction. However, samples collected after a two week maintenance shutdown showed a return to reference levels of MFO activity in both sexes and of steroid levels in male fish. The relationship between elevated MFO activity and depressed steroid levels is unclear, but detailed experiments suggest that the two phenomena are not directly linked. White sucker show depressed steroid production and impaired reproductive regulation independent of MFO activity.