Fatty acid composition of the maternal diet affects egg and larval quality of southern flounder, Paralichthys lethostigma
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Yolk of marine fish eggs is highly concentrated in fatty acids (FAs) that are used for energy, hormone production, and membrane structure. Essential fatty acids (EFAs) are fatty acids that cannot be biosynthesized in physiologically sufficient amounts and must be obtained from the diet. Since EFAs in yolk must originate in the maternal diet, a study was conducted to determine whether changes in maternal dietary docosahexaenoic acid (DHA, an important EFA for proper larval development) during a spawning season had an effect on the proportion of DHA in eggs of Southern flounder, Paralichthys lethostigma. Adult flounder were conditioned on a common diet and then switched to a high DHA diet, low DHA diet, or no change (control) after the first spawn. Spawns were produced weekly and DHA content of the eggs was measured by gas chromatography. Females fed a high DHA diet produced eggs with a significantly higher proportion of DHA after 3 weeks on the experimental diet. DHA in eggs from females fed a low DHA diet decreased for 5 weeks, then increased, suggesting that those females first used dietary DHA to make yolk then shifted to DHA stored in liver or white muscle. In a second study, spawns from the first study were incubated and larvae were reared to 15 and 35 days post-hatching (dph) to determine whether there was a relationship between FA composition of the eggs, FA composition of the larval body, and responsiveness to a visual predatory stimulus. Ratios of DHA to other EFAs (DHA:ARA and DHA:EPA) were positively correlated with larval responsiveness to a simulated predator. The amount of omega-3 docosapentaenoic acid (DPA) in the egg was strongly correlated with the amount of DHA in the larval body at 15 dph, and was significantly correlated with the amount of DHA in the larval body at 35 dph. This research suggests that southern flounder follow a mixed breeding strategy to supply developing eggs with DHA during vitellogenesis, and variability in FA composition of eggs, specifically (n-3) DPA, may influence larval mortality from predation in the wild.