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This study describes the development of an oncorhynchid growth hormone (GH) radioimmunoassay using recombinant chum salmon GH (rsGH) and a rabbit antiserum (TJK-1) raised against this recombinant material. The assay was designed to measure the wide range of circulating immunoreactive GH (IRGH) levels in Pacific salmonids, resulting in a standard curve capable of accurately determining plasma levels of IRGH from 0.5 to 250 ng/mL without dilution. The assay ED50 and ED90 values averaged 13.1 and 0.5 ng/mL, respectively. This radioimmunoassay specifically recognizes oncorhynchid IRGH, showing no cross-reactivity with recombinant porcine and bovine GH, or natural chum salmon prolactin at concentrations up to 10 micrograms/mL. Curves approximately parallel to the standard curve were obtained with purified natural coho salmon GH and plasma from chinook salmon. Recovery of rsGH from plasma was complete over the full range of the standard curve. Intra- and inter-assay coefficients of variation were 6.0 and 12.9%, respectively. Plasma IRGH levels in fed coho salmon were 30.6 +/- 5.3 ng/mL, while those in fish starved for 2 weeks were 132.9 +/- 53.9 ng/mL. Starvation for an additional 4 weeks had no significant effect. Plasma IRGH levels in control rainbow trout injected with saline were significantly higher 45 min post-injection. In contrast, fish injected with recombinant porcine GH exhibited no elevation in IRGH. It is speculated that exogenous GH inhibits the production of endogenous GH.

The relative potency of several androgens to induce the male phenotype in sexually undifferentiated genotypic female chinook salmon were compared in two separate experiments. The aromatizable and nonaromatizable androgens testosterone (T) and 11-ketotestosterone (11-KT), and the synthetic aromatizable and nonaromatizable androgens 17 alpha-methyltestosterone (MT) and 17 alpha-methyldihydrotestosterone (MDHT) were administered to newly hatched alevins in a single 2-hr immersion treatment at doses ranging from 3.2 micrograms/liter to 10 mg/liter. The influence of these treatments on sex differentiation was evaluated by the histological examination of the resulting gonads 6 and 11 months later. In the control group, which was not exposed to exogenous steroids, no males or intersex fish were observed. In contrast, essentially 100% masculinization occurred in groups exposed to MDHT at dosages of 400 micrograms/liter and higher. Treatment with the aromatizable androgen MT resulted in a dose-dependent masculinization, with the production of 100% males at 400 micrograms/liter. However, higher doses resulted in fewer males. 11-KT and T were less potent than the synthetic androgens. The number of males produced after treatment with 11-KT followed a dose-dependent pattern while T showed virtually no masculinizing effect in inducing male phenotype in these studies. The resultant AD50 dosage levels (dosage at which 50% of the genotypic females were sex-reversed into phenotypic males) after a single 2-hr immersion treatment were: 30, 60, and 500 micrograms/liter for MDHT, MT, and 11-KT, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The oral cavity of embryos and larvae of the teleost Onchorhynchus kisutch was examined. Tissues were obtained at different ages prior to and after hatching and processed for transmission and scanning electron microscopy. A bilaterally symmetrical bulge developed from the superolateral aspect of the oral cavity and projected toward its floor, along the sides of the tongue. The bulge extended from behind the primary palate to a position midway below the eye, anterior to the gill arches, and it is suggested to be the homologue of the secondary palate of higher vertebrates. Ultrastructurally, the epithelium differentiated as the stratified squamous type and it contained mucous cells. However, the features of programmed cell death seen during palatogenesis in mammals were absent in fish. The fish palate mesenchyme, unlike that of higher vertebrates, was chondrified. Also in contrast to higher vertebrates, alterations were seen in the fish palatal basement membrane. A transient appearance of adepidermal granules in the lamina lucida region was followed by organization of collagen fibrils, first into an orthogonal pattern and then into a herring-bone arrangement, in the lamina reticularis region. There was no further advancement in the morphogenesis of fish palate. It is suggested that the differences in the morphogenesis and structure of the secondary palates of various vertebrates may reflect environmentally enforced adaptation, resulting in different programming of cells.

Vitellogenin production was induced in immature diploid and triploid coho salmon by the weekly injection of 17 beta-estradiol at 1 mg/kg body wt. There was no significant difference between diploids and triploids for any of the results obtained, i.e., change in plasma vitellogenin and gonadotropin levels, hepatosomatic index, or pituitary gonadotropin content. Plasma vitellogenin levels were significantly higher in 17 beta-estradiol-treated fish than in sham-injected fish within a week of the first injection, and continued to rise with each subsequent injection. Plasma gonadotropin levels, on the other hand, were slightly (but significantly) depressed. The 17 beta-estradiol-treated fish had higher hepatosomatic indices and pituitary gonadotropin contents than sham-injected fish by 3 weeks after the first treatment. These data suggest that the occasional postmeiotic oocytes observed in triploids do not grow to full maturity due, in part, to an absent or diminished estrogen stimulus from the ovary on hepatic vitellogenin production.

Plasma gonadotropin (GtH) levels and state of oocyte development were determined in adult female coho salmon following single intraperitoneal injections of LH-RH or its superactive analog des-Gly10[D-Ala6]LH-RH-ethylamide (LH-RHA DAla6). The peptides injected at dosages of 1.0 or 0.2 mg LH-RH and 0.2 or 0.02 mg LH-RHA DAla6/kg bw elevated plasma GtH by 1.5 hr postinjection. The response to the analog was of longer duration. Plasma GtH levels returned to basal levels 24 hr following LH-RH injection while elevated plasma GtH levels were maintained for at least 96 hr in response to the analog. Only those fish injected with LH-RHA DAla6 showed an accelerated rate of germinal vesicle breakdown (GVBD). Based on their relative effects on GVBD, LH-RHA DAla6 has at least 50 times the biological potency of LH-RH in adult female coho salmon.

17 beta-Estradiol, testosterone, and 17 alpha, 20 beta dihydroxy-4-pregnen-3-one (17 alpha 20 beta P) levels were measured in plasma samples obtained from coho salmon (Oncorhynchus kisutch) during the preovulatory period and following the injection of mammalian gonadotropin releasing hormones. Spontaneous reproductive activity was characterized by a rapid decline in plasma 17 beta-estradiol 10 days prior to ovulation and a large increase in plasma 17 alpha 20 beta P 6 days before ovulation. Testosterone levels remained high (greater than 125 ng/ml) throughout the preovulatory period, with a small peak evident 6 days prior to ovulation. Oocyte development was not accelerated in fish injected with mammalian LH-RH, whereas des-Gly10[D-Ala6]LH-RH-ethylamide (LH-RHA DAla6) promoted germinal vesicle breakdown (GVBD) in 10 out of 14 fish within 96 hr. Only LH-RHA DAla6-injected fish which completed GVBD displayed the characteristic steroid changes observed during spontaneous reproductive activity. In LH-RH-injected fish, there was a transient increase in plasma 17 alpha 20 beta P levels which persisted for less than 24 hr. LH-RHA DAla6-injected fish which failed to complete GVBD maintained high 17 alpha 20 beta P levels, but the peak concentrations were lower than those in fish which completed GVBD. These fish also maintained high plasma 17 beta-estradiol levels when compared to fish which completed GVBD. The appearance of high plasma 17 alpha 20 beta P levels during spontaneous and LH-RHA DAla6-induced reproductive activity was coincident with the time of GVBD. This finding was consistent with the view that 17 alpha 20 beta P functions as the maturation-inducing steroid in salmonids. The induction of GVBD using gonadotropin-releasing hormones was related to the elevation of plasma gonadotropin levels for greater than 24 hr [G. Van Der Kraak, H. R. Lin, E. M. Donaldson, H. M. Dye, and G. A. Hunter (1983) Gen. Comp. Endocrinol. 49, 470-476] and a decrease in 17 beta-estradiol production.

This paper describes an homologous radioimmunoassay for coho salmon vitellogenin that demonstrates parallel cross-reactivity for plasma vitellogenin of all Pacific salmonids tested (chinook, chum, coho, pink, and sockeye salmon, and cutthroat and rainbow trout), but not for Atlantic salmon or two nonsalmonids: common carp and sablefish. Plasma vitellogenin levels were high in ovulatory female Pacific salmonids (micrograms/ml to mg/ml range), but were mostly nondetectable in spermiating males of the same species.