Determining the position of southern flounder Paralichthys lethostigma on the reproductive energy allocation spectrum using an essential fatty acid as a maternal dietary biomarker

Abstract

Energy allocation strategies of fishes during vitellogenesis fall along a spectrum from rapid transfer of ingested nutrients into yolk (income breeding) to drawing upon reserves stored in somatic tissues (capital breeding). Southern flounder, Paralichthys lethostigma, migrate from estuaries to offshore habitats to spawn, likely resulting in variability in nutrient intake. The effect of variable nutrient intake on egg composition depends upon the position of southern flounder on the income—capital breeding continuum. The essential fatty acid docosahexaenoic acid [DHA, 22:6(n-3)] was used as a biomarker to determine energy allocation strategy by measuring whether a shift in maternal diet at the start of the spawning season results in changes in the proportion of DHA in eggs. Treatment groups of flounder were fed a common diet and then switched to a high DHA diet, low DHA diet, or no change (control) diet after the first spawn, and spawned weekly for 8 weeks. DHA content of eggs changed within a few weeks of the diet change to reflect the dietary DHA content, consistent with an income breeding strategy. However, after about five weeks, females receiving the low DHA diet mobilized DHA stored in liver and white muscle tissues to reverse a decreasing trend in DHA content of eggs, evidence of a capital breeding strategy. These results suggest that southern flounder are income breeders under nutritionally favorable conditions but have the flexibility to use somatic stores to build yolk when nutrient availability is limited.