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 wa..., , # Assessing fish movement and physiological traits along a salinity gradient by measuring stable oxygen isotope values in fish blood water and muscle water

Dataset DOI: [10.5061/dryad.fj6q5745h](10.5061/dryad.fj6q5745h)

## Description of the data and file structure

We conducted two experiments to gain a more comprehensive understanding of the behaviour and physiology of migratory fish species. First, we changed the salinity levels of water under a controlled laboratory environment to monitor variations in *δ*18O values in the blood water and muscle water of Japanese eels (Anguilla japonica). Second, we collected wild fish specimens from the river and estuary to evaluate *δ*18O variations in their blood water and muscle water at different salinity levels.

Before blood sampling, 12-mL glass vials used for isotope analyses were flushed with a mixture of helium and 0.25 % reference CO2 with a known isotope value. Subsequently, three to four drops of each blood sample were injected into ...,