Epidermis thickness and secondary sexual characters in mature male and immature Baltic salmon, Salmo salar L., parr: seasonal variations and effects of castration and androgen treatment

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Abstract
At the breeding season (November) the mature male parr had a thicker epidermis than had the immature parr. In winter (February) there was no difference, while in May, at the smoltification period, the previously mature male parr had a thicker epidermis than the immature parr. In both categories of fish the epidermis was thinner in May than in November. The epidermal thickness in castrated male parr was the same as in immature parr. Treatment with 11‐ketoandrostenedione (llkΔ4) increased epidermal thickness in castrated males. Treatment with testosterone and llkΔ4 increased epidermal thickness in previously mature males in spring. There was no development of anadromous secondary sexual characters (hooked lower jaw, adult nuptial colouration) in any male.