Effect of elevated summer temperatures on gonadal steroid production, vitellogenesis and egg quality in female Atlantic salmon

Groups of Tasmanian female Atlantic salmon Salmo salar L. were maintained at 14, 18 and 22degrees C for 3 months from mid-summer (January). Blood plasma levels of 17beta-oestradiol (E-2), testosterone (T), cortisol and vitellogenin (Vtg) were measured at regular intervals, and in autumn (April) temperatures were reduced to 8degrees C to facilitate spawning and egg incubation. Maintenance at 22degrees C during vitellogenesis was associated with a general reduction in plasma E-2 levels and all early reduction in plasma Vtg levels relative to those observed in fish held at 14 and 18degrees C. Significantly reduced oocyte diameters in ova from fish held at 22degrees 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 22degrees C (69 and 42%, respectively) were significantly reduced relative to those of ova from fish maintained at 14degrees C (93 and 86%) and 18degrees C (86 and 84%).