Effects of sexual maturation, castration, and androgen implants on growth in one‐ and two‐year‐old parr in a Baltic Atlantic salmon ( Salmo salar L.) stock

The effects of maturation, castration, and androgen implants on growth in 1‐ and 2‐year‐old Baltic salmon ( Salmo salar L.) were studied in a stock originating from the Umeälven (Ume river) in northern Sweden. 1 + male parr that later matured were larger than non‐maturing parr in the spring. Later in the summer, during the period of gonadal growth, the growth rate of maturing parr was depressed compared to that of non‐maturing males. Implantation of capsules with 11‐ketoandrostenedione (OA) or testosterone (T) in sexually immature 1‐year‐old fish, accelerated the specific growth rate in spring and early summer, particularly considering growth in weight, resulting in an increase in the condition factor. In contrast, the growth rate was depressed from late June onwards, the period when the gonads normally develop in 1 + parr. T, but not OA, also promoted sexual maturation. Castration or OA treatment did not affect total summer growth in 2‐year‐old salmon. This study suggests a causal relationship between androgens and the growth pattern observed in maturing 1 + male parr.