Abstract
The influence of two light regimes, 16:8 h light/dark (LD 16:8) and 24:0 h light/dark (LD 24:0), in comparison to a usual hatchery light regime (HL), on the fatty acids content and weight gain in hatchery-reared underyearlings (at 0+ age) and yearlings (at 1+ age) of Atlantic salmon in the summer–autumn period was studied. The total lipids were analyzed by Folch method, the lipid classes using HPTLC, and the fatty acids of total lipids using GC. The increase in EPA and DHA observed in October in underyearlings and yearlings salmon (especially under LD 24:0) suggests they were physiologically preparing for overwintering. The changes in fatty acids and their ratios in juvenile Atlantic salmon can be used as biochemical indicators of the degree to which hatchery-reared fish are ready to smoltify. These associated with an increase in marine-type specific DHA and EPA, an increase in the 16:0/18:1(n-9) ratio, in correlation with a reduction in MUFAs (mainly 18:1(n-9)). These biochemical modifications, accompanied by fish weight gain, were more pronounced in October in yearlings exposed to continuous light (LD 24:0). The mortality rate was lower in experimental groups of underyearliings with additional lighting. Exposure to prolonged and continuous light did not affect yearlings mortality rate.
Highlights
Many physiological and biochemical processes in fish undergo daily fluctuations, and their activity is governed by the endocrine system [1]
We studied the effect of different light regimes on growth and the content of fatty acids and it is ratios in hatchery-reared underyearlings and yearlings of Atlantic salmon in the summer–autumn period
Noticeable, by the end of September, there was a decrease in the weight gain of the fish in the group 2 (LD 16:8), and in October, their mean mass was significantly lower than the fish in the hatchery light regime (HL) group (Figure 2)
Summary
Many physiological and biochemical processes in fish undergo daily fluctuations (circadian rhythms), and their activity is governed by the endocrine system [1]. Various photoperiod modes trigger the parr–smolt transformation and smoltification, which is associated with elevated endocrine and Na+,K+-ATPase activity [3]; increase in lipid and nitrogen metabolism [4]; changes in the bioconversion of essential fatty acids (FAs) α-linoleic acid (18:3(n-3)) and linoleic acid (18:2(n-6)) into physiologically valuable polyunsaturated FAs (PUFAs) eicosapentaenoic acid (EPA, 20:5(n-3)), docosahexaenoic acid (DHA, 22:6(n-3)), and arachidonic acid (ARA, 20:4(n-6)) [5,6,7,8]; and the growth of young salmon [9,10,11]. For wild salmon juveniles [8], lipid metabolism indices are quite sensitive to changes in the ambient environment. Studying the lipid status in the summer–autumn period is important because this period is decisive for the physiological preparation of young salmonids for their first winter, and can influence the timing of smoltification and the life strategy [15]
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