Effects of crowding on blood constituents and flesh quality variables in Atlantic salmon (Salmo salar L.)

The effects of anaesthesia (as a control treatment) and controlled crowding, with its concomitant low oxygen level, on harvest size salmon (Salmo salar) were compared in terms of blood constituents and flesh quality variables, at 0, 1, 4, 7 and 10 days post-mortem. Fish were held in tanks in triplicate and were sampled after anaesthetizing with AQUIS (R) and after crowding for one hour. Eighteen fish from each treatment were stunned, blood sampled from the posterior aorta and the fish bled by gill cut and filleted. All blood variables with the exception of cortisol were higher (P < 0.05) in crowded fish compared with anaesthetized fish. Initial muscle pH was lower in the crowded fish and only between days 0; 1 and 4. Colour was significantly lighter in crowded than in anaesthetized fish on days 0 and 1. Weight loss was higher (P < 0.05) in the crowded fish and also increased in both treatments with time post mortem. Muscle asthaxantin concentration showed no statistical difference between treatments nor post mortem. It can be concluded that crowding and reduced oxygen level had a negative effect on blood variables and on flesh quality, lowering colour score, lowering initial muscle pH, and increasing the weight loss of fillets.