Endocrine and transcriptome changes associated with growth and differentiation of Atlantic (Salmo salar L.) salmon testes and immune activity of adipose tissue

The study compared salmon reared at different light regiments (groups A, B and D) and fed with feeds with high and low fat (groups D and E). Analyses in pituitaries and testes addressed problem of early sexual maturation in aquaculture. It is marked by dramatic endocrine changes and rapid growth of the testes, resulting in an increase in the gonad somatic index. The study examined the association of plasma sex steroids, pituitary and testicular gene expression with gonadal growth. The key characteristic is developmental stage of testis, from I to IV. In addition, the effect of feeds with high and low fat levels on adipose tissue was compared. The key finding is markedly different immune activity in groups D (high fat) and E (low fat). Salmon post smolts were kept in tanks with brackish water within a flow-through system, with an average salinity of 20 ± 0.4 ppt and mean temperature of 12.1 ± 0.2°C. Different light treatments (constant, increasing and decreasing) were tested during a period of 18 weeks. Sampling was condcuted at the end of this period to asses early sexual maturation traits. This study focused on changes related do different levels of maturity. Various light treatments were explored, including continuous exposure (Group A), increasing exposure (Group B), and decreasing exposure (Groups C, D and E) were investigated on growth and sexual maturation, sampling was performed after 18 weeks to assess gonadal growth and blood steroid hormone levels. All groups were provided with the same feed, except for Group E, which received a low-fat diet.