Potential Effects of Contaminants on Fraser River Sockeye Salmon

Chakravorty et al. (1992) observed declines in plasma vitellogenin levels in femalecatfish (Clarias batrachus) exposed to endosulfan (nominal concentration <strong>of</strong> 1.5 µg/L)for 16 days. Similarly, male sheephead minnows exposed to endosulfan atconcentrations <strong>of</strong> 0.28 to 0.79 µg/L for 40-d did not accumulate detectable levels <strong>of</strong>vitellogenin in their plasma (Hemmer et al. 2001).Hemmer et al. (2001) also evaluated vitellogenin induction in male sheepsheadminnows exposed to methoxychlor at concentrations <strong>of</strong> 5.6 and 12.1 µg/L. Theresults <strong>of</strong> this experiment indicated that the parent compound was not estrogenic.However, the demethylated metabolites can bind to the estrogen receptor. At bothexposure levels, plasma vitellogenin levels increased rapidly, reaching 120 mgvitellogenin/mL <strong>of</strong> plasma in the high exposure group by day 35.Reproductive effects have been observed in fish exposed to the carbamate insecticidecarb<strong>of</strong>uran. In female dwarf gourami (Colisa lalia), 20-d aqueous exposures to thissubstance (i.e., at 0.7 µg/L) resulted in the production <strong>of</strong> fewer mature oocytes and ahigher incidence <strong>of</strong> atresia <strong>of</strong> mature oocytes (oocycte absorption; Sukumar andKarpagaganapathy 1992).Exposure to DDTs is also known to cause reproductive effects in fish. Cheek et al.(2001) exposed Japanese medaka to nominal concentrations <strong>of</strong> 2,4'-DDT rangingfrom 0 to 7.5 µg/L for two or eight weeks after hatching. The results <strong>of</strong> this studyshowed that 8-week exposures to this substance induced vitellogenin production in all<strong>of</strong> the treatment groups. Female-skewed sex ratios were observed at the two highestdoses, while an increased incidence <strong>of</strong> ovotestis was observed in fish exposed to 1.94µg/L <strong>of</strong> 2,4'-DDT for eight weeks. Dietary exposure <strong>of</strong> Atlantic croakers(Micropogonias undulatus) to 0.02 or 0.1 µg 2,4'-DDT/g BW/day for three or sevenweeks resulted in increased plasma gonadotropin hormone levels and increased ovarysize (as indicated by gonadosomatic index scores; Khan and Thomas 1998).In chinook salmon, short-term exposure to 2,4'-DDT (at 10 mg/L) at fertilization (1-hexposure) and at hatch (2-h exposure) did not adversely affect mortality rate, time tohatch, fish length, or fish weight at one month following first feeding (Milston et al.2003). Similarly, sex ratios, gonadal development, and concentrations <strong>of</strong> plasmaestradiol and 11-ketotestosterone were unaffected by the treatment. However, earlylife stage exposure to this substance resulted in long-term humoral immuneincompetence (i.e., immunosuppression) in chinook salmon, which could increase92