ANNUAL SEX STEROID PROFILES AND EFFECTS OF GENDER AND SEASON ON CYTOCHROME-P450 MESSENGER-RNA INDUCTION IN ATLANTIC TOMCOD (MICROGADUS TOMCOD)

As a preliminary step in a 4-year biomonitoring program, sex steroid l evels (testosterone and 11-ketotestosterone in males, and testosterone and estradiol in females), gonad weights, and diameter of vitellogeni c oocytes were measured in tomcod collected bimonthly from the Miramic hi (industrialized site) and Kouchibouguac (reference site) rivers fro m September 1993 to September 1994. As well as the reproductive indice s, hepatic levels of cytochrome P4501A mRNA (CYP1A mRNA) were also mea sured. The preparatory period for spawning began in September, with ma ximal steroid levels in November, and spawning took place from late De cember to January. The CYP1A mRNA levels in female tomcod appeared inv ersely related to plasma steroids, with the lowest amounts of CYP1A mR NA coinciding with maximal steroids. The CYP1A mRNA levels in male tom cod did not exhibit this relationship. River-river comparisons of fema le tomcod showed significantly smaller vitellogenic oocytes in the Mir amichi, along with lower plasma testosterone, estradiol, and relative gonad weight. Miramichi CYP1A mRNA levels were higher than Kouchibougu ac in the fall but lower in the spring sample. The CYP1A mRNA-sex ster oid relationship observed in this study will facilitate meaningful int erpretation of data collected during the full 4-year study.