H.R. King

High prevalence of skeletal deformity and reduced gill surface area in triploid Atlantic salmon (Salmo salar L.)

Abstract The prevalence of skeletal deformity throughout the development of different populations (all-female triploid, mixed-sex triploid, all-female diploid and mixed-sex diploid) of Tasmanian Atlantic salmon (Salmo salar L.) was determined to elucidate the possible effects of ploidy or sex status on the incidence of deformity. Populations were produced and maintained under commercial conditions in freshwater until individuals had attained a wet weight of approximately 80 g, at which time each population was divided and either retained in freshwater (FW smolt) or transferred to seawater (SW smolt), where fish were held for a further 2 months. Whole fish were sampled throughout this period from hatching (470° days post-fertilisation). The prevalence of skeletal deformities was significantly higher in triploid populations. Jaw deformity, including lower jaw deformity syndrome (LJD), occurred in up to 2% of triploid fry, 7% of triploid FW smolt, 14% of triploid SW smolt and 1% of diploid FW smolt. The prevalence of LJD was highest in triploid FW smolt. Short opercula were observed in up to 22% of triploids and 16.6% of diploids. Up to 60% of triploids and 4% of diploids suffered from the absence of primary gill filaments (gill filament deformity syndrome (GFD)) during FW development prior to SW transfer, then, up to 50% of triploid FW smolt and 60% of triploid SW smolt suffered from GFD. There was no significant difference in the sex ratio of each deformity type. An index of gill surface area (GSA) was significantly reduced in normal triploids and triploids afflicted with GFD, compared to diploid counterparts. It is likely that the reduction of GSA affects an individuals capacity for metabolic gas exchange under vigorous exercise or suboptimal environmental conditions.

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

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 (E2) 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 stocks 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 E2 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 E2 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.

Effects of dbcAMP on steroidogenesis in isolated ovarian follicles of Atlantic salmon

In vitro estradiol-17β (E2) and testosterone (T) production were measured in vitellogenic follicles of Atlantic salmon in response to treatment with human chorionic gonadotropin (hCG) and 2-0-dibutyryladenosine 3′,5′-cyclic monophosphate (dbcAMP). DbcAMP stimulated T production but had no effect on E2, whereas hCG treatment stimulated E2 production but T production was low. Elevated intracellular [cAMP] may be part of the normal mechanism for inhibition of aromatase activity at the end of vitellogenesis.