This dataset is associated with the manuscript entitled: Growth, Osmoregulation, and Ionoregulation of Longfin Smelt (Spirinchus thaleichthys) Yolk-sac Larvae at Different Salinities Contact: Yuzo Yanagitsuru, yyanagit@ucdavis.edu, yuzo.yanagitsuru@gmail.com All analyses were conducted in R version 3.6.3 Description of column headers for each tab: waterandsodium: Salinity - salinity condition in ppt that fish were reared in Time - hours post-transfer. 0 refers to pre-exposure (i.e. post-hatch still in 0.4 ppt [freshwater] salinity) Clutch - clutch/cross identification (i.e. id for different pairs of male/female broodfish) Container - container id in which fish were held WetWeight - total wet mass of 10 individuals in ug DryWeight - total dry mass of 10 individuals in ug WaterContent - percent water content calculated from WetWeight and DryWeight TotalNaContent (umol) - total sodium content in umol from 10 individuals Naconc (umol/g) - sodium concentration calculated by dividing TotalNaContent with DryWeight. DryWeight was divided by 1000000 to convert ug to grams. This was then divided by 10 to calculate average individual Naconc values from the grouping of 10 fish that were measured. morphometrics: Salinity - salinity condition in ppt that fish were reared in Time - hours post-transfer. 0 refers to pre-exposure (i.e. post-hatch still in 0.4 ppt [freshwater] salinity) Clutch - clutch/cross identification (i.e. id for different pairs of male/female broodfish) Container - container id in which fish were held Calibration SL - length in pixels of electron microscopy grid area used for calibrating pixels to mm from images Calibration # squares - number of squares on electron microscopy grid measured for calibration of images from pixels to mm. Each square was 200 micrometers Calibration # bars - number of bars on electron microscopy grid measured for calibration of images from pixels to mm. Each bar was 50 micrometers. Notochord length (pixels) - pixel length of fish measured from image Yolk length (pixels) - pixel length of fish yolk length Yolk depth (pixels) - pixel length of fish yolk depth Yolk width (pixels) - pixel length of fish yolk width Calibration NL - The coefficient used to convert pixels to mm. Calculated as the length in micrometers of electron microscopy grid measured (200 micrometers * no. squares + 50 micrometers * no. bars) divided by the pixel length of electron microscopy grid measured. Calibration 8x - The coefficient used to convert pixels to mm for yolk length, width, and depth. A single calibration image was used and was calculated in the same way as described for Calibration NL. 8x indicates the magnification used for measuring all yolk dimensions. NL - notochord length in mm used for analyses. Calculated multiplying Notochord length (pixels) with Calibration NL. Divided by 1000 to convert micrometer to mm. YolkV - yolk volume in nL used for analyses. Calculated using the ellipsoid equation: 4/3*pi*(1/2 length)*(1/2 width)*(1/2 depth). Length, width, and depth were multiplied by Calibration 8x to convert pixels to micrometers. The volume calculated was multiplied by 10^-6 to convert micrometer cubed to nanoliters Survival: Time - time in hours post-transfer to salinities. 0 indicates pre-transfer to salinities. Salinity - salinity condition in ppt that fish were reared in Survival - percentage of individuals from a group of 30 that were alive. Calculated as number of fish alive divided by 30 and multiplied by 100.