DOI: 10.5061/dryad.fj6q5745h
title: 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

description: 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.
description: # 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 the flushed glass vials and
 stored in a fridge. Before the isotope analyses, the samples were
 incubated at 24 °C for 24 hours, ensuring *δ*18O equilibrium between
 sample and reference CO2. Headspace sampling was performed, and the
 obtained samples were analysed using the Delta V plus system (Thermo
 Fisher Scientific, Germany) equipped with Gasbench II (Thermo Fisher
 Scientific) at the Atmosphere and Ocean Research Institute, the University
 of Tokyo. When fish samples were sacrificed or collected from the field,
 they were stored in the freezer immediately. After the fish samples were
 defrosted at room temperature, dorsal muscle (approximately 110 mg) was
 collected and soaked with a paper towel to avoid the contamination from
 other fluids, such as water and blood. Subsequently, the samples were
 placed in glass vials. The muscle samples were placed in glass vials and
 then treated in the same manner as the blood samples. Specifically, the
 muscle samples were flushed with a mixture of helium and CO2, incubated at
 24 °C for 24 hours, and analysed using an IRMS system equipped with a
 GasBench system at the Atmosphere and Ocean Research Institute, the
 University of Tokyo. Experimental_water.csv | **Column name** |
 **Description** | **Units** | **Data format** | **Missing data code** | |
 :-------------- |
 :-------------------------------------------------------------------------------------------- | :-------- | :-------------- | :-------------------- | | SampleID | The water sample is named according to the date of collection in the format (year.month.day). | - | Category | - | | Salinity | The salinity of the experimental water. | PSU | Number | - | | Day | The start date of the experiment. | - | Number | - | | d18O | Stable oxygen isotope values in water. | ‰ | Number | - |  Experimental_Japanese_eel.csv | **Column name** | **Description** | **Units** | **Data format** | **Missing data code** | | :-------------- | :----------------------------------------------------------- | :-------- | :-------------- | :-------------------- | | PIT name | The ID number of pit tag | - | Category | - | | Day | The start date of the experiment. | - | Number | - | | Type | Sample types, such as blood or muscle. | - | Category |   | | d18O | Stable oxygen isotope values in blood water or muscle water. | ‰ | Number | - |  Amami_water. csv | **Column name** | **Description** | **Units** | **Data format** | **Missing data code** | | :-------------- | :----------------------------------------------------------------------------- | :-------- | :-------------- | :-------------------- | | Name | The water sample is named according to the location of collection. | - | Category | - | | Area | Sampling locations, including Shidokan Port, Shidokan River, and Yamato River. | - | Category | - | | d18O | Stable oxygen isotope values in environmental waters. | ‰ | Number | - | Amami_fish.csv | **Column name** | **Description** | **Units** | **Data format** | **Missing data code** | | :-------------- | :----------------------------------------------------------------------------- | :-------- | :-------------- | :------------------------------------------------------------------------------------------ | | Sample Name | The fish sample is named according to the location of collection. | - | Category | - | | Species | Fish species. | - | Category | - | | Area | Sampling locations, including Shidokan Port, Shidokan River, and Yamato River. | - | Category | - | | b.d18O | Stable oxygen isotope values in blood water. | ‰ | Number | "NA" indicates the failure of blood extraction. | | m.d18O | Stable oxygen isotope values in muscle water. | ‰ | Number | "NA" indicates the failure of muscle extraction (insufficient amount for isotope analyses). |