Androgens in teleost fishes

The olfactory hypothesis of the salmonids' homing assumes that the juvenile is conditioned to recognize a specific scent of its native river during the smolt stage and that it uses this characteristic to locate its river for upstream migration. We tested this hypothesis and exposed, in artificial conditions, some farmed coho salmon, rainbow trout and fario trout, aged 18 months, to a chemical (morpholine or alcoolphenetyl) introduced in the natural production environment (mixed with the scents of the native river), in order to determine if they will be responsive to this product to locate their initial production environment during upstream migration.

Olfactory imprinting and homing in salmon

Publisher Summary This chapter discusses that the gonads potentiality to produce steroids, and the regulation of the syntheses. The nature, shape, and intensity of a hormonal signal, ready to be received by a target cell, is the result of an intricate series of positive and negative regulations. In the case of hormonal steroids in fish, only some aspects of this complex have been considered. Once a steroid is secreted, several mechanisms may inactivate it before it reaches its target. Little is known of catabolism of sexual steroids in teleosts. Most available data are concerned with the total radioactivity found in tissues after fish are fed labeled steroid. The biological significance of glucuronidation or sulfonation remains to be explored. Although the conjugated steroids are usually considered to be inactive, recent studies attribute a pheromonal role to glucuronides. In other respects, the binding to plasma proteins may lead to a reversible inactivation, although, in mammals, it has been suggested that steroid secretion may be enhanced by the presence of serum steroid-binding proteins. Finally, the conversion of plasma steroids into biologically active metabolites can occur in some target tissues. The actual physiological role of gonadal steroids in fish is discussed with emphasis on gametogenesis.

7 The Gonadal Steroids

Hypothalamic control of the pars distalis in fishes, amphibians, and reptiles.

Publisher Summary Results of in vitro investigations have conclusively shown that certain steroids are potent stimulators of oocyte final maturation in fish. Although phylogenetic differences exist in the stimulation of final maturation by steroids, in at least eight different species representing several teleost orders, the most effective steroid yet tested for the induction of final maturation is 17α,20β-DHP. From in vitro investigations, gonadotropins appear to stimulate final maturation, in most fish directly at the ovarian level, although in at least one species, the Indian catfish, the stimulation appears to be through the interrenals. That gonadotropins stimulate final maturation by stimulating follicular steroidogenesis has been confirmed by several methods. Further, increases in circulating gonadotropin levels correlate well with final maturation and ovulation in several species.

3 Hormonal Control of Oocyte Final Maturation and Ovulation in Fishes

Stimulation of pituitary gonadotropin by testosterone in juvenile rainbow trout (Salmo gairdneri).

The plasma gonadotropin profile during sexual maturation in a variety of salmonid fishes

LH-RH-Stimulated gonadotropin release from the rainbow trout pituitary gland: An in vitro assay for detection of teleost gonadotropin releasing factor(s)☆

D.M. Evans

Papers

Stimulation of pituitary gonadotropin by testosterone in juvenile rainbow trout (Salmo gairdneri).

The plasma gonadotropin profile during sexual maturation in a variety of salmonid fishes

LH-RH-Stimulated gonadotropin release from the rainbow trout pituitary gland: An in vitro assay for detection of teleost gonadotropin releasing factor(s)☆