Metabolic endocrine factors involved in spawning recovery and rematuration of iteroparous female rainbow trout (Oncorhynchus mykiss)

Abstract

To determine how energy balance affects metabolic hormones hypothesized to play a role in the onset of a new reproductive cycle in iteroparous salmonids, food availability after spawning was restricted in female rainbow trout. These fish were compared with a control group that was fed a standard brood stock ration. Bodyweight, length, and muscle lipid content were determined, and blood was collected from fish at regular intervals; a subset of fish from each group was sacrificed at each sampling time for the collection of liver and ovary tissue, and to calculate hepatosomatic index (HSI) and gonadosomatic index (GSI). Plasma hormone levels were quantified by radioimmunoassay, and tissue gene expression levels were analyzed using q-RT-PCR. The experiment was conducted twice, using two-year-old and three-year-old post-spawned fish. Food-restriction arrested ovarian growth and development within 15–20weeks, as evidenced by lower GSI in restricted-ration fish. Food restriction also reduced Fulton’s condition factor, muscle lipid content, and specific growth rate from one month onward, and reduced HSI after 3months. In the liver, insulin-like growth factor (igf1 and igf2) gene expression was reduced in three-year-old food-restricted fish within 2months; however, no effect of ration on igf1 or igf2 expression was detected in two-year-old fish. In both years, IGF binding protein-1 (igfbp1) gene expression decreased over time in both treatment groups. Liver leptin (slepA1) gene expression was lower in two-year-old food-restricted fish at 4months. These results show that this feed restriction regime arrested reproductive development and affected factors associated with energy balance purported to play a role in initiating reproductive development within 2–4months after spawning.