The ecological significance of lipid/fatty acid synthesis in developing eggs and newly hatched larvae of Pacific cod (Gadus macrocephalus) |
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Authors: | Benjamin J Laurel Louise A Copeman Thomas P Hurst Christopher C Parrish |
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Institution: | (1) Fisheries Behavioral Ecology Program, Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA, Hatfield Marine Science Center, Newport, OR 97365, USA;(2) Ocean Sciences Centre, Memorial University of Newfoundland, Logy Bay, NL, A1C 5S7, Canada |
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Abstract: | The lipid/fatty acid composition of marine fish eggs and larvae is linked with buoyancy regulation, but our understanding
of such processes is largely restricted to species with pelagic eggs. In this study, we examined developmental changes in
the lipid/fatty acids of eggs and embryos of Pacific cod (Gadus macrocephalus), a species that spawns demersal eggs along coastal shelf edges, but as larvae must make a rapid transition to the upper
reaches of the water column. Adult Pacific cod were collected in the Gulf of Alaska during the spawning season and eggs of
two females were artificially fertilized with sperm from three males for each female. The eggs were subsequently reared in
the laboratory to determine (1) how lipids/fatty acids were catabolized during egg and larval development, and (2) whether
lipid/fatty acid catabolism had measurable effects on egg/embryo density. Eggs incubated at 4°C began hatching after 3-weeks
and continued to hatch over a 10-day period, during which there was a distinct shift in lipid classes (phospholipids (PL),
triacyglycerols (TAG), and sterols (ST)) and essential fatty acids (EFAs: 22:6n-3 (DHA), 20:5n-3 (EPA), and 20:4n-6 (AA)).
In the egg stage, total lipid content steadily decreased during the first 60% of development, but just prior to hatch we observed
an unexpected 2–3-fold lipid increase (~6–9 μg individual−1) and a significant drop in egg density. The increase in lipids was largely driven by PL, with evidence of long-chained fatty
acid synthesis. Late-hatching larvae had progressively decreasing lipid and fatty acid reserves, suggesting a shift from lipogenesis
to lipid catabolism with continued larval development. Egg density measures suggest that lipid/fatty acid composition is linked
to buoyancy regulation as larvae shift from a demersal to a pelagic existence following hatch. The biochemical pathway by
which Pacific cod are apparently able to synthesize EFAs is unknown, therefore representing a remarkable finding meriting
further investigation. |
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