Comparison of aspects of the physiology and morphology of diploid and triploid Atlantic salmon Salmo salar

High mortality rates under suboptimal culture conditions and the incidence of lower jaw deformity (LJD) are problems associated with the commercial production of all female triploid Atlantic salmon (Salmo salar) within the Tasmanian Atlantic salmon industry. The current study investigates the primary and secondary haematological stress responses, the skeletal ontogeny and the incidence of skeletal deformity in fish from different population types (all-female diploids, all-female triploids, mixed sex diploids and mixed sex triploids), throughout development, up until 7 weeks post-sea water (SW) transfer. Plasma cortisol (F) levels of rested freshwater (FW) parr (n = 10) were less than `10` `ng.ml^-1` and were subsequently elevated in parr subject to 1 hour 20 minutes of confinement, regardless of sex or ploidy status. Rested all-female diploid SW smolt (n = 10) had significantly lower plasma F levels than rested all-female triploid, mixed sex diploid, and mixed sex triploid SW smolt. In all SW smolt, plasma F and plasma lactate levels were elevated following 1 and 3 hours of confinement, but were statistically similar to rested levels following 6 hours of confinement. In a subsequent experiment, plasma F levels of diploid and triploid SW smolt (n = 7) subject to 2 hours of confinement, decreased to rested levels within a 6 hour recovery period, post-treatment. Haematological parameters were measured in SW smolt from different populations following 2.5 h confinement in aerated SW. Plasma cortisol levels, plasma lactate and glucose levels increased following confinement, irrespective of ploidy status. Total blood haemoglobin (Hb) was lower in all-female triploid fish compared to all-female diploids, however there was no difference between mixed sex groups. There was no difference in haematocrit (Hct), mean cell haemoglobin concentration (MCHC), whole blood adenosine triphosphate concentration [ATP], Hb:ATP and total plasma protein between diploid and triploid individuals. In-vitro examination revealed the blood oxygen affinity (`P_(50)` values) and percentage oxygen saturation of Hb at various physiological pH levels were similar between diploid and triploid smolt. Blood viscosity was dependant on Hct and shear rate, irrespective of ploidy status. These results show there is no difference in the primary or secondary stress responses of S. salar with ploidy status. Furthermore, blood oxygen carrying capacity and the extent of anaerobic metabolism did not differ with ploidy status under these experimental conditions. The gross morphology and ossification of the lower jaw, cranium, branchial apparatus and fin skeleton throughout ontogeny is described for each population type. There appeared to be no differences in the skeletal ontogeny of normal diploid and triploid fish. Triploid Atlantic salmon were susceptible to significantly higher incidence of deformity post-first feeding compared to diploid fish. Short opercula were observed in up to 20% of fish from each population post-first feed, regardless of ploidy or sex status, where as gill filament deformity syndrome (GFD), occurred almost exclusively in triploid fish, at rates of up to 60%. Triploid fish with either normal gills or gills affected by GFD had a lower gill surface area index than diploid salmon. LJD was detected almost exclusively in triploid smolt cultured under either FW and SW conditions, following the time of SW transfer. It is unlikely that the primary endocrine and secondary haematological stress responses or the aerobic capacity of triploid fish contribute to high mortality under suboptimal commercial conditions. The repercussions of decreased gill surface area on ionoregulation or respiration in triploid fish under conditions of hypoxia and/or exhaustive exercise are discussed.