Data from: Assessing fish movement and physiological traits along a salinity gradient by measuring stable oxygen isotope values in fish blood water and muscle water

Variations in stable oxygen isotopes (δ18O) in the body water of animals
reflect changes in δ18O values in environmental water and the animals’
physiological processes. Euryhaline/anadromous/catadromous fish species
move across salinity gradients; changes in δ18O values in environmental
water thus lead to changes in δ18O values in body water. Few studies have
systematically evaluated the effect of salinity on δ18O values in fish
body water. Accordingly, this study demonstrated a well-established
approach to investigating the relationship between salinity and δ18O
values in fish body water (blood water and muscle water). This
study comprised two experimental designs. First, we implemented continual
changes in salinity levels to assess the corresponding variations in δ18O
values in the blood water of Japanese eels under controlled laboratory
conditions. Second, field (river and estuary) studies were conducted for
multiple fish species on Japan’s Amami Island. Samples of fish blood water
and muscle water were analysed in accordance with a general headspace
protocol to estimate δ18O values; this estimation was conducted using
isotope ratio mass spectrometry, which involved an equilibration method
for sample preparation. The data include the difference in δ18O
values in fish blood water, muscle water and ambient water in the
laboratory experiment involving changes in salinity and in the field
collection from the Amami Island. Analysing δ18O values in environmental
water, blood water, and muscle water is useful for monitoring the
behaviours of regional migratory fish, such as temporary feeding in
estuaries. Our analytical method is ideal for measuring δ18O values in
fish body water because it enables analysing various organic tissues by
using small amounts of body fluids, facilitating the examination of the
ecology of aquatic animals.