Male Coho Salmon (Oncorhynchus kisutch) Exposed to a Time-Course of Urban Sewage Effluent Exhibit a Sporadic Low Incidence of Sex Reversal and Intersex

Abstract

Abstract Developing coho salmon alevin (Oncorhynchus kisutch) were exposed to concentrations of 1 to 10% municipal wastewater effluent (MWWE) during the labile period of sexual differentiation. MWWE was collected at regular time intervals from a municipal wastewater treatment plant during a 4-week period that coincided with the latter part of the spawning season of coho salmon. The salmon were exposed, from just prior to hatch until 28 d post hatch, to MWWE collected at 3 a.m., 8 a.m., 3 p.m. or 8 p.m. Subsequent gonadal development was assessed by histology and compared to genetic sex as determined by Y-chromosomal DNA markers. The MWWE (analyzed using GC-HRMS) had relatively high concentrations of steroidal estrogens and other endocrine active substances at some time points during the exposure period. A low incidence of intersex and sex reversal was noted in the coho salmon exposed to MWWE collected at only two time points; 3 a.m. (1% MWWE) and 8 p.m. (10% MWWE), and ≤19% of the male fish in these exposure groups were affected. The coho salmon utilized were of wild genetic backgrounds and thus the sporadic nature of the response observed may be due to a significant genetic influence on the ability to respond to exogenous hormones at this early stage of development.