Efficiency and Rate of Yolk Utilization by Developing Embryos and Larvae of the Pacific Sardine <i>Sardinops caerulea</i> (Girard)

Abstract

The chemical composition of ripe Pacific sardine ovaries, composed primarily of yolk, is almost identical to that of yolk extracted from planktonic sardine embryos and larvae. Caloric measurements were made on ripe ovaries and the values obtained were used to estimate the caloric content of individual sardine embryos and larvae.Water content of sardine egg and larval yolk averages 91.2%. An egg with a yolk volume of 0.56-mm 3 has a caloric reserve of 0.30 calorie when spawned. Caloric uptake from the embryonic and larval yolk was measured against time, and caloric utilization due to catabolic processes was analysed by indirect calorimetry (oxygen consumption) with changing embryological development and swimming activity. The caloric value of the remaining yolk 160 hours after spawning; (at 14 °C) is not sufficient to completely support the sardine larva's catabolic processes. This deficit is made up by resorption of tissue and is reflected in a loss of larval weight. Yolk is converted into tissue with an average assimilation coefficient of about 79%.