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)
- Institution
- The University of North Carolina Wilmington (UNCW )
- Web Site: http://library.uncw.edu/
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.
Phosphorus composition and fatty acid profiles as determinants of egg quality in southern flounder Paralichthys lethostigma
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Created on 1/1/2009
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Additional Information
- Publication
- Thesis
- 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
- Keywords
- Southern flounder--Larvae, Southern flounder--Research
- Subjects
- Southern flounder -- Research
- Southern flounder -- Larvae