Sterile triploid Atlantic salmon represent a solution to the issues of pre-harvest sexual maturation and mature escapees from open aquaculture systems. Although the initial problems of reduced performance and increased deformities in triploids have been thoroughly researched, there is a continued lack of information on their susceptibility and response to disease and routine on-farm treatments compared to diploids. Thus, the main aim of this thesis was to enhance the current understanding of triploid health and immunity through experimental disease challenges and treatments, and aid in determining their robustness and, therefore, suitability for aquaculture.
A commercial furunculosis vaccine equally protected diploids and triploids against challenge with Aeromonas salmonicida, and adhesion scores were similar between ploidy (Chapter 2). Interestingly, triploids had lower white blood cell counts but increased cellular activity, e.g. respiratory burst, compared to diploids. Following experimental cohabitation infection with Neoparamoeba perurans, causative agent of Amoebic Gill Disease (AGD), ploidy did not affect the manifestation or severity of AGD-associated gill pathology, or the serum innate immune response (Chapter 3). Hydrogen peroxide, used to treat against parasitic diseases, elicited similar primary and secondary stress responses in both ploidy, but led to differences in the expression of stress (cat, gpx1, gr, hsp70, sod1, sod2) and immune (saa5, crp/sap1a, crp/sap1b, il1β) genes (Chapter 4). Finally, vaccination with different vaccine treatments (4 commercial vaccines, 6 different vaccine combinations and a sham-vaccinated control) showed no ploidy differences in adhesion score or antibody response, although vertebral deformities remained higher in triploids (Chapter 5). Increasing severity of vaccine treatments negatively affected weight, length and thermal growth coefficient in both ploidy. Triploids were heavier than diploids at smolt (+ 14 %) and post smolt (+ 32 %).
Overall, this research shows that triploid Atlantic salmon respond as well as diploids to disease and treatment challenges, and supports their application into full-scale commercial aquaculture