Stress response of red sea bream Pagrus major to acute handling and chronic photoperiod manipulation

Abstract

A number of primary and secondary features used as stress indicators in fish were investigated in red sea bream, Pagrus major exposed to different photoperiod regimes. In Experiment 1, fish weighing from 17 to 25 g were subjected to acute stress consisted of netting the fish from the rearing tanks and confinement in a small tank (30 L) half-full of water. The fish were then sampled at 0.5, 1, 4, 24, 48, and 72 h post-stress to investigate the stress-induced levels of different parameters. In Experiment 2, fish were exposed to different photoperiods (6L : 6D, 12L : 12D, 16L : 8D and 24L : 0D) for eight weeks. Blood samples were collected from the fish at the 1st, 4th and 8th week after exposure to the photoperiods. Acute stress significantly increased the plasma levels of cortisol (190.1 ng ml − 1 ) and glucose (109.5 mg dl − 1 ) and returned back to the basal levels within 24 h. In contrast, plasma levels of cholesterol (180.5 mg dl − 1 ), total protein (3.0 g dl − 1 ), potassium (4.1 mMol l − 1 ) and Ca ++ (11.3 mg dl − 1 ) were decreased significantly and returned to levels indistinguishable from those of control within 72 h except cholesterol, which did not recover within 72 h. In Experiment 2, fish exposed to 6L : 6D, 16L : 8D and 24L : 0D photoperiods had significantly higher cortisol levels than those exposed to the 12L : 12D photoperiod during the first week ( P < 0.05); however, there was no major difference in cortisol levels among the treatments during other sampling times. There were no significant differences in other parameters among the treatments during the course of the study ( P > 0.05). Fish exposed to the 24L : 0D photoperiod showed significantly higher weight gain and SGR followed by 16L : 8D, 6L : 6D and 12L : 12D photoperiods. The plasma levels of different stress indicators in different photoperiods in Experiment 2 were far lower than those of acute stress-induced levels observed in Experiment 1. On the other hand, no apparent signs of chronic stress were observed in fish exposed to different photoperiods. The results demonstrated that photoperiod manipulation caused no significant acute or chronic stress response in red sea bream.