The concept of animal welfare has been given much attention in the last few years. It is beneficial to practise good fish welfare in aquaculture to achieve good fish health, low mortality, good quality and high profitability. Artificially produced triploid salmon, with an extra set of chromosomes, is sterile and produced to prevent genetic interactions with wild populations. The full biological effects of having an extra chromosome set are largely unknown, but triploids are considered more sensitive to sub-optimal environmental conditions.
This study aimed to investigate the effect of an acute allostatic load on the HPI–axis of diploid and triploid Atlantic salmon smolts (Salmo salar L.). Five hundred smoltified (0+) Atlantic salmons were used in the experiment. The experiment consisted of four groups (in triplicate): control diploid, control triploid, stress diploid and stress triploid. The stress groups were exposed for 20 minutes, crowding stress, and distributed to different tanks for sampling after 0, 1, 2, 3, 4, 6, 12, 24, 48 and 72 hours. Diploid and triploid had elevated plasma cortisol concentrations, but the triploid salmon showed significantly greater values than diploids. The results of this study indicate that triploid Atlantic salmon smolts exposed to an acute allostatic load result in an allostatic overload between type 1 and type 2 responses with a temporary oversensitivity to ACTH and a reduced negative feedback system, with a temporarily reduced regulatory ability of divalent ions. Although no negative tertiary stress responses like reduced growth or increased mortality were detected in this experiment, the oversensitive triploid salmon might quickly end up in an allostatic overload type 2 (chronic stress) followed by compressed welfare if subjected to a stronger or longer-lasting stressor. The refore, t he triploid salmon should be handled as gently as possible with the lowest stress load possible to prevent the animal welfare of this ploidy salmon from becoming compromised.