10:45 AM - 12:15 PM
[MIS09-P03] Otolith strontium isotopes reveal homing behavior of crucian carps in Lake Biwa
Keywords:strontium isotopes, Fish otolith, Spawning migration, River water
Carassius auratus grandoculis, the fish endemic to Lake Biwa, are thought to have evolved from Carassius auratus langsdorfii, a widespread species throughout Japan. In the Lake Biwa basin, Carassius auratus langsdorfii migrates freely along rivers and shallow lakeshores. On the other hand, Carassius auratus grandoculis hatches at rice fields connected to rivers and lakeside swamps, and then migrates offshore of Lake Biwa to forage for food.
When spawning, some individuals have been observed to return to their natal waters with pinpoint accuracy (unpublished data). We called this spawning migration “natal homing.” These individuals are thought to have olfactory memory of the chemical composition of water, specific to their natal waters (unpublished data).
The purpose of this study was to estimate the migration history of each individual, in order to confirm the life cycle differences between the related crucian carps and to calculate the natal homing rate of Carassius auratus grandoculis. Thus, we foucused on strontium isotopes as the tracing method.
It is known that the 87Sr/86Sr ratio in river water well reflects the geological time of the watershed.
On the other hand, fish otoliths have accumulated some of the elements taken into their bodies as they grow, and do not lose the past information. They also have characteristic annual ring structure that reflects the progression and stagnation of growth.
Therefore, by measuring the strontium isotope ratios of otoliths (lapilluses) and comparing them with those of river and lake water, it is possible to chronologically trace the water areas through which individuals have migrated.
In this study, crucian carp individuals and water samples were collected at six canals over multiple days from April to June. The crucian carp individuals can be divided into three categories: adult Carassius auratus grandoculis, adult Carassius auratus langsdorfii, and newborn Carassius auratus grandoculis. The lapilluses of the newborns were sampled as they were. Adult lapilluses were processed into thin slices exposing the central core cross, and further drilled along the annual ring structure in order to obtain powder samples for each time series.
Comparison of strontium isotope ratios between newborn lapilluses and river water showed a general tendency to approximate each other, although there was a large degree of variation. In addition, the isotope ratios of adult Carassius auratus grandoculis were found to be consistent between their juvenile stage and the river water sample where they returned. This suggests their high-resolution natal homing.
At this time, we don’t have sufficient data on both adult crucian carps, so we refrain from making any specific conclusions.
When spawning, some individuals have been observed to return to their natal waters with pinpoint accuracy (unpublished data). We called this spawning migration “natal homing.” These individuals are thought to have olfactory memory of the chemical composition of water, specific to their natal waters (unpublished data).
The purpose of this study was to estimate the migration history of each individual, in order to confirm the life cycle differences between the related crucian carps and to calculate the natal homing rate of Carassius auratus grandoculis. Thus, we foucused on strontium isotopes as the tracing method.
It is known that the 87Sr/86Sr ratio in river water well reflects the geological time of the watershed.
On the other hand, fish otoliths have accumulated some of the elements taken into their bodies as they grow, and do not lose the past information. They also have characteristic annual ring structure that reflects the progression and stagnation of growth.
Therefore, by measuring the strontium isotope ratios of otoliths (lapilluses) and comparing them with those of river and lake water, it is possible to chronologically trace the water areas through which individuals have migrated.
In this study, crucian carp individuals and water samples were collected at six canals over multiple days from April to June. The crucian carp individuals can be divided into three categories: adult Carassius auratus grandoculis, adult Carassius auratus langsdorfii, and newborn Carassius auratus grandoculis. The lapilluses of the newborns were sampled as they were. Adult lapilluses were processed into thin slices exposing the central core cross, and further drilled along the annual ring structure in order to obtain powder samples for each time series.
Comparison of strontium isotope ratios between newborn lapilluses and river water showed a general tendency to approximate each other, although there was a large degree of variation. In addition, the isotope ratios of adult Carassius auratus grandoculis were found to be consistent between their juvenile stage and the river water sample where they returned. This suggests their high-resolution natal homing.
At this time, we don’t have sufficient data on both adult crucian carps, so we refrain from making any specific conclusions.