Effect of sea water temperature on egg size of Japanese anchovy.

Abstract

Egg size change of Japanese anchovy dependent upon sea water temperature is described. Length of chorion was selected as the representative egg size character based on comparisons with some other characters, and referred to as egg diameter. Egg diameter changed seasonally and geographically. Mean egg diameter of net samples had significant negative correlation with surface water temperature. This correlation seemed to be universal regardless of time and locality. Spawning experiments confirmed the effect of temperature on egg size. Yearly variation of egg size spawned in an aquarium corresponded to trend of temperature anomalies of each year. Egg size could be experimentally enlarged by cooling rearing water. Stability of the anchovy population was discussed in connection with reproductive strategy. Egg size change through temperature information seemed to be beneficial to reproduction from the viewpoint of abundance of food and predator and size of food organisms. The strategy regard-ed as the key to stability was that reproductive energy was invested dispersally to long spawning season. This strategy was based on the ability to accumulate reproductive energy quickly and on the eurythermal nature of the species.