Effect of Photoperiod Advancement of Atlantic Cod Spawning on Egg Size and Biochemistry

Abstract

We report on the proximate composition, lipid class, and fatty acid content of fertilized eggs during the course of one spawning season from two broodstocks of Atlantic cod Gadus morhua: One group was maintained under ambient photoperiod (PP), whereas for the second group the natural photoperiod cycle was compressed by approximately 4 months by PP advancement from ambient. We tested the hypothesis that PP compression, which reduces the time between successive spawning seasons and therefore reduces the time available for vitellogenesis and maturation, might also impair nutrient transfer to the eggs, causing reduced egg quality as measured by biochemical indices. Advanced PP eggs were significantly larger than ambient control eggs (absolute mean values for dry weight = 109.2 and 97.9 μg, respectively). Advanced PP eggs also had significantly greater mean total protein (60.0 versus 49.4 μg), mean total lipid (15.1 versus 9.7 μg), and greater mean values for several major lipid classes (hydrocarbons, triacylglycerols, sterols, diacylglycerols, and phospholipids) than ambient controls. Proportionally (percent of dry weight), mean total lipid, ash, triacylglycerols, total saturated fatty acids, and total polyunsaturated fatty acids, including total ω-3, total ω-6, docosahexaenoic acid, eicosapentaenoic acid, and arachidonic acid, were all significantly greater in eggs of the advanced PP group than in ambient controls. The latter contained proportionally more monounsaturated fatty acids. Mean dry weight of eggs declined over time from onset of first spawning in the ambient PP group but not in the advanced PP group, and none of the measured biochemical indices varied significantly over time from onset of first spawning in either PP group. We conclude that with the PP advancement technique used here, compression of time between successive spawnings by up to 4 months in Atlantic cod does not negatively affect biochemical indices of egg quality associated with normal development or survival performance.