Nutritional status of Atlantic salmon (Salmo salar) broodstock. Maternal effects on early expression of leptin, IGF-I, IGF-IR, and GHR
In fish and other vertebrates the IGF-I/GH axis plays an integral role in regulating differentiation, growth and reproduction. In mammals, leptin is a peptide hormone produced by adipocytes, which indicates the nutritional status. The effect of nutritional status on age at 1st maturity (puberty) is postulated to reflect the action of unknown metabolic signal(s) that are recognized by the brain and serve as indicators of metabolic state. In rats leptin receptors have been reported in the brain as well as in the ovary and testis; hence leptin may act as a metabolic signal to the reproductive system acting through the brain-pituitary-gonad axis and directly on the gonads. In this trial we wanted to look at the early expression of leptin, IGF-I and the receptors IGF-IR and GHR. Three females were sampled at spawning and their offspring followed until 2 weeks after first feeding (FF). The results showed leptin expression in Atlantic salmon larvae prior to the onset of exogenous feeding (FF). Leptin expression increased during the endogenous feeding stage, but after onset of exogenous feeding expression of leptin declined. To our knowledge, this is the first time leptin has been detected and followed up in early developmental stages of Atlantic salmon. An expression profile similar to leptin was also found for IGF-I, as well as for the receptors (IGF-IR and GHR).