Energy metabolism in eggs and larvae of the Senegal sole

Oxygen consumption in Solea senegalensis increased during the egg stage reaching values close to 4 nmol O₂ ind^?1 at hatching. After hatching, larval oxygen consumption continued to increase, reaching a maximum rate of 9.97^?1±87 nmol O₂ ind^?1 h^?1 2 days after the opening of the mouth. Body nitrogen content decreased mainly after exhaustion of yolk reserves. Carbon content decreased during the whole endogenous feeding phase, although it decreased twice as quickly after yolk-sac absorption. The free amino acid (FAA) depletion rate was higher during egg development and the yolk-sac period. Complete yolk absorption coincided with the consumption of the 90% of initial FAA content in the eggs and the remaining FAA were consumed at a lower rate. Based on stoichiometrical calculations, FAA appears to be the most important energy substrate during the egg stage (86%) in the Senegal sole. During the period from hatching to the mouth opening, contributions of FAA and lipids as metabolic fuels were similar (41 and 47%, respectively). The decrease in larval protein content during starvation indicates that amino acids from body protein are used as energy substrates under food deprivation.