Growth Retardation (Stunting) in Coho Salmon: Plasma Hormone Levels in Stunts in Seawater and after Transfer to Fresh Water.
Plasma levels of prolactin (PRL), growth hormone (GH), cortisol, thyroxine and triidothyronine were measured in normally-growing seawater (SW) and freshwater (FW) smolts and in animals which had stunted after premature transfer to SW. PRL levels were highest in FW animals and there was no difference between SW stunts and smolts. GH levels were 4-5-fold higher in stunts than in FW or SW smolts. Thyroid hormones and cortisol were significantly lower in stunts. Interrenal activity, assessed in vitro, was depressed in stunts. Transfer of stunts into FW for 3 weeks resulted in a normalization of plasma hormone levels. The results are discussed in relation to the possible causes of stunting and the involvement of the endocrine system in growth retardation.