Ovarian growth and plasma sex steroid and vitellogenin profiles during vitellogenesis in Tasmanian female Atlantic salmon ( Salmo salar)

Abstract

In order to provide detailed information on the reproductive development of female Atlantic salmon ( Salmo salar) in Tasmania, Australia, fish were sampled from sea cages during the main period of vitellogenesis over the austral summer and autumn (October–March). Plasma levels of the gonadal steroids 17β-estradiol (E 2) and testosterone (T), and vitellogenin (Vtg), as well as a range of indices of ovarian development, were measured. Somatic growth and gonadal development were consistent with the stock's growth and development as an austral autumn spawning stock. Mean body weight increased from 3.4 to 5.4 kg and gonadosomatic index (GSI) increased from 0.5% to 17%. Plasma levels of E 2 and T increased from ∼3 to ∼20 ng ml −1 and plasma levels of Vtg increased from ∼2.5 to greater than 35 mg ml −1. However, increases in GSI, oocyte volume, etc., tended to occur later than expected on the basis of Northern hemisphere data and plasma levels of E 2 and T did not increase significantly until the last month of sampling. Plasma levels of Vtg were also static (∼10 mg ml −1) during mid-summer (December–January). Together these observations indicate possible temperature-related impairment of reproductive development during summer.