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Effect of egg size on size and viability of newly hatched medaka (oryzias latipes) and surf smelt (Hypomesus pretiosus pretiosus) Stanley, Richard David


The relationship between egg size and larval viability, as inferred from size at hatching, resistance to starvation, and growth, was studied in the Medaka, Oryzias latipes (Temminck and Schlegel) , and the Surf Smelt, Hypomesus pretious pretiosus (Girard). Medaka larvae which hatched from heavier eggs were larger at hatching, but did not survive longer during starvation. When the larvae were fed a small and varied food, neither relative growth rate nor relative body depth was correlated with original egg weight. However, when larvae were fed a large mobile prey, Paramecia multimicronucleatum, the larger the egg they came from the faster they grew. Thus, the advantage of large size at hatching is partially a function of the feeding conditions at hatching. In Surf Smelt, egg weight was correlated with maternal age. Two-year-old females produced eggs that were 50% heavier than those of one-year-old females, and hatchlings that were heavier and almost 1 mm longer. Smelt larvae with the most yolk reserve (yolk vol/length) at hatching survived longer, and the amount of reserve was correlated with egg dry weight. The larvae failed to feed in the laboratory. The effect of egg size on larval growth suggests that uncontrolled variation in egg size would affect experimental results, and may be important in commercial fishery management.

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