The color change and stress response of Atlantic salmon (Salmo salar L.) infected with Aeromonas salmonicida

Abstract

Fish challenged with pathogens often show behavioral disorders. The present study investigated the influence of Aeromonas salmonicida infection on the body color changes of Atlantic salmon (Salmo salar L.). In both conditions of a white background and transfer from the black background to the white background, the body color contrast of the fish infected with A. salmonicida (100 μL bacterium solution 8.2 × 109 CFU ml−1 in the dorsal muscle) declined significantly following an initial increase compared with the control group (100 μL 0.9 % NaCl); the greatest differences were observed on day 11, at 57.6 % and 52.7 % respectively (P<0.01). In the black background (transferred from white to the black background), A. salmonicida infection resulted an initial lower and then higher contrast in the challenged fish (P<0.01), and the greatest difference occurred on day 5, reaching 156.7 % (P<0.01). Meanwhile, the cortisol, melanocyte stimulating hormone (MSH) and melanin-concentrating hormone (MCH) levels in serum were also evaluated. Comparing the infected fish with the control fish, the cortisol (7.2 % ∼ 21.2 %), MSH (25.8 % ∼48.6 %) and MCH (36.4 % ∼ 54.4 %) levels of the infected fish were elevated to varying degrees after infection with A. salmonicida (P < 0.05). The results suggested that A. salmonicida challenge altered the color-change behavior, which might be regulated by MSH and MCH.