Abstract
Continuous photoperiod is extensively used in fish farming, to regulate the reproductive cycle, despite evidence suggesting that artificial photoperiods can act as a stressor and impair the immune system. We evaluated the potential effects of an artificial photoperiod on mucus components: lysozyme and mucin, in juvenile rainbow trout (Oncorhynchus mykiss) after exposure for one month to natural photoperiod (LD12:12) or constant light (LD24:0) artificial photoperiod. For each treatment, we assessed changes in peripheral blood cells (erythrocytes and leukocytes) and skin mucus component concentrations. Our results show a decrease in lysozyme concentration, while mucin levels are increased. Similarly, we find elevated monocytes and polymorphonuclears under constant light photoperiod. These findings suggest that LD24:0 regulates lysozyme, mucin, and leukocytes, implying that artificial photoperiods could be a stressful.
Highlights
The light-dark cycle is one of the most important inputs that control many biological activities in fish [1,2]
Hematocrit and erythrocytes show a trending increase from day 0 to 14 in both treatment groups, no statistically significant differences were observed at each time point between treatment groups (Figure 2A,B)
Regarding the white blood cell counts (WBC), total leukocyte numbers decrease in fish maintained under artificial photoperiod within 3 days of exposure and until day 7, Regarding the white blood cell counts leukocyte compared to the natural photoperiod group. (WBC), At daystotal
Summary
The light-dark cycle is one of the most important inputs that control many biological activities in fish [1,2]. Salmonids are normally raised under constant light (light, L; dark, D = LD24:0) since the first feeding to accelerate growth during the freshwater phase. The onset of smoltification is triggered using constant light (LD24:0), followed by a period of artificial winter (LD12:12) during six to eight weeks, and followed by additional six weeks in LD24:0 [7]. The application of artificial photoperiod is considered a clean technique, a recent study in trout estimated mortality rates over 25% in fish subjected to artificial photoperiods compared to mortality rates of 7% in fish maintained in natural light cycles [9,10]. Application of artificial light indues stress that leads to immunosuppression and leaves salmonids and Nile tilapia prone to diseases [8,10,11,12]
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