摂餌開始期のカタクチイワシ仔魚の生残能力に対する卵サイズの影響

Abstract

The effect of egg size on the survival potential of first feeding Japanese anchovy Engraulis japonicus larvae was analyzed by rearing experiments. Measuring egg length (L: mm; major axis of chorion) and width (S: mm; minor axis), egg volume (V: mm3) was evaluated by V=π/6×L×S2. The egg lengths and the evaluated volumes of eggs were used as the egg size indexes.The standard length (SL: mm) of the unfed larvae increased during the first three days after hatching and later decreased at 20°C. The SL at the third day (Max. SL) increased with increasing egg size. The correlation of Max. SL was more noticeable with egg length than evaluated egg volume. The survival time of the unfed anchovy larvae also increased with increasing egg size. The correlations between mean survival time and two indexes of egg size were both significant.The feeding potential of the first feeding larvae was assessed by the feeding index (relative volume of rotifers in a gut) and the percentage of feeding success (percentage of larvae with rotifers in a gut). Both indexes increased with increasing egg size, suggesting that larger larvae which are hatched from larger eggs have a higher feeding potential than smaller ones.Larger anchovy larvae from larger eggs have a higher survival potential, and may be advantageous for surviving, especially under poor feeding conditions.