Testing the synergistic effects of GnRH and testosterone on the reproductive physiology of pre‐adult pink salmonOncorhynchus gorbuscha

Abstract

To test the hypothesis that the hypothalmic gonadotropin-releasing hormone (GnRH) and testosterone (T) co-treatment stimulates both the hypothalmo-pituitary-gonadal (HPG) and hypothalmo-pituitary-interrenal axes, the reproductive and osmoregulatory responses of pre-adult pink salmon Oncorhynchus gorbuscha were compared after GnRH and T administration either alone or in combination. Relative to controls, neither GnRH nor T treatment resulted in significantly greater ovarian or testicular growth, but co-treatment significantly increased ovarian growth after 5 months. Interestingly, the stimulation was undetectable after 3 months. However, once daily photoperiod began shortening after the summer solstice, c. 2 months before the natural spawning date, GnRH+T-treated females were stimulated to produce larger ovaries. Final fish body length and the size of individual eggs did not differ among treatment groups. GnRH+T eggs, however, showed signs of advanced vitellogenesis relative to GnRH-treated and control eggs, whereas T-treated eggs became atretic. Testis size increased significantly from initial values and most males were spermiating, but this growth and development were independent of hormone treatments. Final plasma ion, metabolite and cortisol concentrations did not differ among treatment groups. It is concluded that GnRH+T co-treatment was effective in stimulating female but not male maturation. GnRH and T treatment, however, presumably had little effect on the hypothalmo-pituitary-interrenal axis as observed by ionoregulatory status.

Gonadotropins in the Russian Sturgeon: Their Role in Steroid Secretion and the Effect of Hormonal Treatment on Their Secretion

“…These results are in line with other studies in juvenile or sexually resting teleosts that showed that GnRHa more effectively stimulates pituitary LH/LHβ when combined with T [ 55 – 58 ]. In the pink salmon ( Oncorhynchus gorbuscha ), neither GnRH nor T resulted in significantly greater ovarian or testicular growth, but their co-administration significantly increased ovarian growth after 5 months [ 59 ]. The combination of GnRH + T also increased E2 levels in the Russian sturgeon.…”

Physiological profiles of sockeye salmon in the Northeastern Pacific Ocean and the effects of exogenous GnRH and testosterone on rates of homeward migration

“…There was no obvious relationship between treatment type and migration success: 13 fish reached northern Vancouver Island (6 non-hormone enhanced, 7 hormone enhanced) and 4 of these fish actually entered the Fraser River (2 non-hormone enhanced, 2 hormone enhanced). We did not expect to see an effect of hormone enhancement on migration survival of sockeye because of the results of a preliminary study we conducted in which we examined the physiological effect of exogenous injections of GnRH and testosterone on reproductive and osmoregulatory physiology of maturing saltwater residing pink salmon (O. gorbuscha; Crossin et al 2009b). In that study, 250 salmon were divided into four treatment groups (GnRH, GnRHþT, T and control/sham) and survival during the nearly 5-month long experiment was 490% in all treatments groups (Crossin et al 2009b).…”

“…We did not expect to see an effect of hormone enhancement on migration survival of sockeye because of the results of a preliminary study we conducted in which we examined the physiological effect of exogenous injections of GnRH and testosterone on reproductive and osmoregulatory physiology of maturing saltwater residing pink salmon (O. gorbuscha; Crossin et al 2009b). In that study, 250 salmon were divided into four treatment groups (GnRH, GnRHþT, T and control/sham) and survival during the nearly 5-month long experiment was 490% in all treatments groups (Crossin et al 2009b). Thus, we must look beyond the experimental treatments to the pre-release physiological information and handling procedures, to the environmental conditions during migration and to fisheries exploitation in order to shed light on our results.…”

Conservation physiology of animal migration

“…The photosensitive pineal gland entrains information about photoperiod and controls melatonin secretion, which tracks circadian and circannual changes ( Bradshaw and Holzapfel, 2007 ; Tosches et al ., 2014 ; Winkler et al ., 2014 ). In turn, melatonin stimulates androgen production ( Crossin et al ., 2010 ), a primary cue for the breeding migration of fish and birds ( Wingfield et al ., 1990 ). Among birds, melatonin concentrations regulate migratory restlessness (i.e.…”