Biochemical changes associated with embryonic and larval development in the American lobster Homarus americanus Milne Edwards
Sasaki, Glenn Craig
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Proximate analysis was carried out on developing Homarus americanus Milne Edwards larvae and eggs. Lipids were further analyzed for class and fatty acid composition. During embryogenesis, triacylglycerol supplied most of the energy and the fatty acid 20:5 was selectively utilized. Absence of prolonged cold incubation temperatures resulted in increased yolk reserves in newly hatched larvae. Weight, ash, protein, carbohydrate and lipid varied in association with the larval molt cycle. Scant metabolic reserves were accumulated in premetamorphic larvae while large triacylglycerol reserves were stored in postmetamorphic (fourth stage) animals. Absolute levels of metabolic reserves limited the extent of their utilization. Triacylglycerol was the preferred (first used) energy substrate but was usually limited in amount; hence protein was the major source of metabolic energy during starvation in premetamorphic larvae. Dietary intake of carbohydrate and possibly protein based gluconeogenesis were responsible for most chitin synthesis as established carbohydrate reserves were not sufficient. Triacylglycerol served mainly as an energy storage form. P. choline appeared to exist in two metabolic pools; one of which could be catabolized without concomitant tissue loss. P. ethanolamine and sterols were primarily associated with cellular membranes. During tissue catabolism (starvation), P. ethanolamine was catabolized but sterol was conserved. On average, P. ethanolamine fatty acids were the most unsaturated, followed by the fatty acids of P. choline and then triacylglycerol. The type of fatty acid may influence food consumption and rates of absorption. Compared to a diet containing 16:0, one containing 20:5 was related to greater consumption and faster lipid absorption. The fatty acid pattern of the larvae was heavily influenced by diet. The fatty acids 16:0, 18:0, 20:4, 20:5, and 22:6 were conserved under starvation. Conservation of the saturated fatty acids was probably related to control of cellular membrane fluidity. 16:0 and 18:0 were probably used to compensate for the increased membrane unsaturation from the conserved, potentially essential 20:4, 20:5, and 22:6 fatty acids.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January 1984
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