Fig. 7. Activity of the pituitary–gonadal axis (PG axis) in winter chum salmon in the Gulf of Alaska in terms of (A) the amounts of glycoprotein 2 (GP2), follicle-stimulating hormone β (FSHβ) and luteinizing hormone (LHβ) mRNAs, FSH and LH in the pituitary and (B) the plasma level of FSH, testosterone (T), 11-ketotestosterone (11KT) and estradiol (E2). Fish were collected in February 2006, and divided into immature fish and maturing adult I on the basis of histological features of the gonads. Samples from the winter chum salmon were assayed together with those from the maturing Bering fish in 2003 (N=5 in each sex) for comparison of data with the summer fish in the Bering Sea. Value are means ± s.e.m. See Table 1 for the number of fish.