Changes in yolk total proteins and lipid components and embryonic growth rates during lobster (Homarus americanus) egg development under a simulated seasonal temperature cycle

From August 2000 to June 2001, seven egg-carrying female lobster (Homarus americanus) from the Iles de la Madeleine population (Gulf of St. Lawrence, Canada) were held under a simulated seasonal temperature cycle to monitor egg development from extrusion to hatching. For the first time, changes in the yolk components (total lipids and major lipid classes, total proteins) and embryo growth of single eggs were monitored separately over the entire development period. Under the controlled temperature conditions, egg development proceeded in three phases. (1) Autumn, from extrusion to early December, was marked by a rapid increase in the Perkins's eye index and rapid declines in yolk total proteins and triacylglycerols (TAG). Embryo daily growth rate was estimated between 1 and 2 mug proteins day(-1). (2) Winter, from late December to early April (temperature stable at ca. 1degreesC) was characterized by a stationary phase in the evolution of the eye index and yolk lipid use, and embryo growth slowed significantly. (3) Spring, from late April to hatching in June was the period with the most rapid changes in yolk TAG and embryo growth rates >6 mug proteins day(-1) were recorded. Almost 65% of the live biomass (total proteins) of the hatching larvae was accumulated during the last few weeks of development. An index of embryo growth efficiency was estimated as the slope of the relationship between embryo total proteins and yolk TAG during egg development. A relationship was found between the initial mean egg dry weight and the embryo growth efficiency index suggesting that under the same experimental conditions bigger eggs used yolk lipids more efficiently and sustained faster embryonic growth than smaller eggs. The relationship may also explain why larger larvae originate from larger eggs.