Larger eggs at lower water temperature as a measure to assure effective hatchling size in the landlocked form of Ayu, <Emphasis Type="Italic">Plecoglossus altivelis</Emphasis> |
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Authors: | Kei’ichiro Iguchi |
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Institution: | (1) Ueda Station, National Research Institute of Aquaculture, Ueda Nagano, 386-0031, Japan |
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Abstract: | Egg size is a critical life-history trait in which maternal investment is optimized to maximize maternal fitness. The adaptive
significance of variable egg size among spawning groups of Ayu (Plecoglossus altivelis) landlocked in the Lake Biwa system was examined through field investigations and rearing experiments. Observed egg size
variations were explained by the water temperature around spawning grounds established near the mouths of inlet streams. Two
typical streams with different incubation temperatures showed similar maternal body sizes and hatchling sizes, but eggs attached
to the stream bed were larger in the colder stream. An experiment that used eggs from a single clutch showed that a smaller
hatchling size was obtained with a lower incubation temperature, indicating that the effect of differences in egg size on
hatchling size can be canceled out by variations in incubation temperature. In general, larvae that are less than a certain
threshold of effective body size are not expected to be assured of early success among conspecifics competing for foods. It
is proposed that environments in which the incubation temperature varies favor variability in egg size to ensure that sufficient
food is accessible to larvae. |
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