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Phosphorus composition and fatty acid profiles as determinants of egg quality in southern flounder Paralichthys lethostigma

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Christopher A. Woolridge (Creator)
The University of North Carolina Wilmington (UNCW )
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Abstract: We used in vivo 31P-NMR to examine biochemical events during development in embryos of southern flounder Paralichthys lethostigma. Adult southern flounder broodstock held under an artificial photothermal regime simulating natural seasonal changes spawned volitionally or following hormone induction by LHRH-a. Buoyant eggs were collected and incubated in 34-ppt seawater at 16º C, and their fertilization rate was monitored. Eggs of a prescribed developmental stage were transferred from the incubator to aerated seawater in a 5-mm NMR tube, and spectra were collected immediately. 31P-NMR peaks were observed for inorganic phosphate (Pi), the a, ß, and ?-phosphates of ATP, NAD(P)H, phosphocreatine (PCr), sugar phosphates, and the phospholipids: phosphatidylcholine (PC), phosphatidylinositol (PI), and phosphatidylethanolamine (PE). Levels of PC, PI, and a, ß, and ?-phosphates of ATP, remained at relatively constant levels in unfertilized eggs over time. However, in eggs that were fertilized, there was a significant increase in PE as they developed, which was not observed in unfertilized eggs. Using the chemical shift of the Pi peak, intracellular pH (pHi) was determined. In fertilized floating eggs the pHi decreased from 7.1 (15 h post-spawn) to 6.2 (24 h post-spawn) and then increased to 6.8 (48 h-post-spawn). ATP showed an inverse relationship with pH, starting to decline when pH reached its minimum value. This suggested that ATP was used to stabilize embryonic pH through active transport of nitrogenous waste, such as ammonia, outside of the developing embryo. By the pre-hatching embryo stage, the ATP phosphates, PCr, and NAD(P)H levels declined to undetectable levels, indicating an embryonic requirement for these compounds. Fatty acid profiles during development in embryos were also examined using HPLC. Lipid and fatty acid composition were compared between embryos (blastula stage) of high quality (fertilization rate = 91.5%, survival to first feeding = 39.0%) and low quality (fertilization rate = 39.0%, survival to first feeding = 13.1%). The most abundant fatty acids (proportion of total fatty acids) included, 16:0 (palmitic acid, 21.5%), 18:1 n-9 (oleic acid, 17.5%), and 22:6 n-3 (docosahexanoic acid, DHA, 26.1%). There were no significant differences (P > 0.05) between low and high quality embryos in total lipids (4.4% wet wt), DHA (26.7%), EPA (3.3%) and ARA (1.9%) and DHA/EPA ratio (8.3). There were no significant differences (P > 0.05) in total lipid and fatty acid profiles in high quality eggs at the blastula, gastrula, early embryo, and late embryo stages. In summary, southern flounder eggs that were viable were characterized by an increase in PE during development and decreasing levels of ATP, PCr, and NADP(H). The increase in PE is possibly a way to conserve DHA important to neuro-visual tissue development. Southern flounder eggs contained high levels of polyunsaturated fatty acids, mainly DHA. High levels of the saturate, palmitic acid, as well as the monounsaturate, oleic acid were also present. Fatty acid profiles were not correlated with egg quality. Lack of significant decreases in phospholipids and fatty acids during embryogenesis suggested that other components (e.g. glycogen and free amino acids) accounted for embryonic energy needs. We hypothesize that in southern flounder, lipid is conserved for utilization after hatching, and that catabolic substrate consumption in embryos starts with glycogen, followed by free amino acids, and then lipid after hatching. We further hypothesize that this pattern may be characteristic of subtemperate marine fish eggs with an oil globule.

Additional Information

A Thesis Submitted to University of North Carolina Wilmington in Partial Fulfillment Of the Requirements for the Degree of Master of Science
Language: English
Date: 2009
Southern flounder--Larvae, Southern flounder--Research
Southern flounder -- Research
Southern flounder -- Larvae