| Summary: | Knowledge regarding the influence of external and internal factors on teleost fecundity may contribute to increased production and efficiency in aquaculture.Teleost plasma cortisol levels may be elevated in response to stress, potentially affecting reproduction through a negative impact on vitellogenesis. Melatonin (MEL), on the other hand, is shown to have protective effects in organisms, and large amounts of MEL has been observed in the gastrointestinal tract (GIT) in various species, hence finding its way to the liver.The subject of this thesis was to document the MEL concentration in Atlantic salmon (Salmo salar) vena portae, and compare this to MEL in the circulating blood. Further, the effect of MEL and cortisol on 17beta-estradiol (E2) stimulated vitellogenin (Vtg) mRNA expression in hepatocytes from Atlantic salmon, was investigated in vitro.The presence of MEL in vena portae was documented, seemingly independent of light conditions and pineal MEL levels.A decrease in Vtg mRNA expression was observed in hepatocytes exposed to cortisol after preincubation with E2 and MEL. This effect was not seen in hepatocytes exposed to cortisol after preincubation with E2 alone.
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