Abstract
Groups of Tasmanian female Atlantic salmon Salmo salar L. were maintained at 14, 18 and 22° C for 3 months from mid‐summer (January). Blood plasma levels of 17β‐oestradiol (E 2 ), testosterone (T), cortisol and vitellogenin (Vtg) were measured at regular intervals, and in autumn (April) temperatures were reduced to 8° C to facilitate spawning and egg incubation. Maintenance at 22° C during vitellogenesis was associated with a general reduction in plasma E 2 levels and an early reduction in plasma Vtg levels relative to those observed in fish held at 14 and 18° C. Significantly reduced oocyte diameters in ova from fish held at 22° C (5·4 mm cf . 5·7 mm) confirmed reduced maternal investment, and an increase in the incidence of previously undescribed chorion damage suggested that zonagenesis may also have been impaired. As a result, the fertility and survival of ova from fish exposed to 22° C (69 and 42%, respectively) were significantly reduced relative to those of ova from fish maintained at 14° C (93 and 86%) and 18° C (86 and 84%).