Effect of Exposure Timing on Fathead Minnow (Pimephales promelas) Reproduction During a Life-Cycle Bioassay with Biologically Treated Bleached Kraft Pulp Mill Effluent

摘要

The investigation described in this paper was designed to determine if the timing of the exposure to pulp mill effluent alters the reproduction response of fathead minnows (Pimephales promelas) and if bioaccumulation of effluent components is likely to be responsible for effects on reproduction. This study was also designed to provide basic information about the mechanisms of effects by evaluating the reproductive fitness of males and females during exposure to effluent. Fathead minnow eggs were exposed to control water and post secondary treatment 100% bleached kraft mill effluent to begin a life-cycle test. Exposure of larvae and juveniles in control water and 100% effluent continued for 75 days, when prespawning adults could be separated into spawning groups, approximately 10 days before spawning began. Spawning groups placed in control water consisted of: 1) control males and females, 2) effluent exposed males and females, 3) effluent exposed males with control females, and 4) control males with effluent exposed females. Identical spawning groups were placed in 100% effluent. Egg production was significantly reduced in each group of fish exposed to 100% effluent during the spawning period compared to all control groups. None of the groups exposed in control water during spawning had significantly different egg production compared to others in control water. Groups exposed in effluent during spawning also had no differences in egg production between other effluent-exposed groups. These data indicate that long-term bioaccumulation of effluent components was not responsible for effects found during this life-cycle test. Reproductive fitness of males and females was unaltered by exposure to effluent before spawning began, and changes in reproduction were the result of low egg production by females. Egg size, gonadosomatic indices of males and females, in-vitro steroid production by the testes, condition factors of males and females and liver-somatic indices of males were not altered during this life-cycle test. Vitellogenin plasma concentrations in males were not altered by the effluent indicating estrogenic and androgenic compounds capable of affecting this parameter were not present in the effluent.