Pj. Williams et al., ANNUAL SEX STEROID PROFILES AND EFFECTS OF GENDER AND SEASON ON CYTOCHROME-P450 MESSENGER-RNA INDUCTION IN ATLANTIC TOMCOD (MICROGADUS TOMCOD), Environmental toxicology and chemistry, 17(8), 1998, pp. 1582-1588
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.