DOI: 10.5061/dryad.4xgxd25k9
title: Data from: Arithmetic normalization models for the effects of lipid on carbon stable isotope values in silver carp (Hypophthalmichthys molitrix) tissue

description: Invasive silver carp (Hypophthalmichthys molitrix) threaten Mississippi
 River basin ecosystems due to their ability to outcompete native species.
 Stable carbon (δ13C) and nitrogen (δ15N) isotope analysis has been used in
 prior studies to help identify how silver carp impact native ecosystems,
 however lipids in fish tissues commonly bias their δ13C values. Chemical
 lipid extraction and mathematical equations that normalize δ13C values for
 lipid content are common ways to account for the effect of lipid on tissue
 stable isotope values in fish, though species and tissue-specific
 arithmetic models have not yet been derived for silver
 carp. Using paired t-tests, we assessed differences in δ13C,
 δ15N, and C:N ratios before and after chemical lipid extraction in muscle
 and whole fish from silver carp collected along three sites in the
 Mississippi River. We then used linear and natural log models to estimate
 lipid-extracted δ13C values in carp muscle and whole fish samples based on
 their non-lipid-extracted δ13C values and elemental C:N ratios. We
 evaluated these arithmetic models for best fit and parsimony and used
 paired t-tests to assess accuracy between mathematically normalized and
 chemically lipid-extracted δ13C values. We found that chemical
 lipid extraction increased silver carp δ13C values and decreased C:N ratio
 in muscle and whole fish as well as increasing δ15N values in whole fish
 but not fish muscle. While both linear and natural log regression models
 accurately estimated lipid extraction δ13C in both sample types, the
 natural log approach provided better model fits and greater parsimony
 throughout the wide range of C:N ratios observed in silver carp. Our
 results confirmed the need to account for lipid-effects on δ13C values in
 silver carp tissue. Moreover, the arithmetic models provided by our study
 will allow future researchers to conduct stable isotope analysis on silver
 carp without the added time and cost of chemical lipid-extraction. In
 addition, the positive relationship we identified between fish muscle and
 whole fish will facilitate the comparison of stable isotope values in
 silver carp across studies.
description: Thirty-two silver carp from three regions (one in Illinois and
 two in Louisiana) along the Mississippi River watershed were collected in
 2023 and 2024. Each fish was thawed, weighed, and measured and aliquots of
 white muscle and whole ground fish were sampled, freeze-dried and split in
 half to create a replicate for lipid extraction. Lipids were chemically
 extracted using Soxhlet extraction overnight (22-24 hours) in a 2:1
 chloroform-methanol solvent and air-dried upon removal. Dry weights were
 taken before and after lipid extraction to calculate the percentage of
 lipid as a function of each samples dry weight. Whole fish and fish muscle
 samples were analyzed before (NLE) and after lipid extraction (LE) for
 carbon (C) and nitrogen (N) elemental concentration (%C and %N) and ratios
 (C:N) as well as stable isotope values (δ<sup>13</sup>C,
 δ<sup>15</sup>N) using an elemental analyzer system coupled to
 a continuous-flow stable isotope ratio mass spectrometer.
description: # Data from: Arithmetic normalization models for the effects of lipid on
 carbon stable isotope values in silver carp (Hypophthalmichthys molitrix)
 tissue
 [https://doi.org/10.5061/dryad.4xgxd25k9](https://doi.org/10.5061/dryad.4xgxd25k9) ## Description of the data and file structure Thirty-two silver carp from three regions (one in Illinois and two in Louisiana) along the Mississippi River watershed were collected in 2023 and 2024. Each fish was thawed, weighed, and measured and aliquots of white muscle and whole ground fish were sampled, freeze-dried and split in half to create a replicate for lipid extraction. Lipids were chemically extracted using Soxhlet extraction overnight (22-24 hours) in a 2:1 chloroform-methanol solvent and air-dried upon removal. Dry weights were taken before and after lipid extraction to calculate the percentage of lipid as a function of each samples dry weight. Whole fish and fish muscle samples were analyzed before (NLE) and after lipid extraction (LE) for carbon (C) and nitrogen (N) elemental concentration (%C and %N) and ratios (C:N) as well as stable isotope values (δ13C, δ15N) using an elemental analyzer system coupled to a continuous-flow stable isotope ratio mass spectrometer. ### Files and variables #### File: Seghers\_et\_al\_RCMS\_Dryad\_dataset.csv **Description:** Definitions of dataset terms are found in the table below. "NA" in a cell indicates not applicable or not available data. Contact [polito@ucsc.edu](mailto:polito@ucsc.edu) if questions. ##### Variables: Description | Units * Sample_ID: Individual sample code| None * Fish_ID: Individual fish code| None * Species: Scientific species name| None * Common_name: Common species name| None * Collection_year: Year when samples were collected| None * Collection_season: Season when samples were collected| None * Sample_Type: Tissue sample analyzed (muscle or whole fish)| None * Collection_state:  State where samples were collected| None * Collection_location: Location code were collected| None * Total_length_cm: Total length measurement of fish | cm * Fork_length_cm: Fork length measurement of fish | cm * Standard_length_cm: Standard length measurement of fish | cm * Fish_mass_g: Total mass measurement of fish | g * lipid%_DW: Sample lipid content as percentage of dry weight| % * NLE_C%: Carbon (C) elemental concentration in non lipid extracted (NLE) sample as percentage of dry weight |% * NLE_δ13C: Carbon (C) isotopic value in non lipid extracted (NLE) sample expressed in the delta (δ) notation | ‰ * NLE_N%: Nitrogen (N) elemental concentration in non lipid extracted (NLE) sample as percentage of dry weight | % * NLE_δ15N:  Nitrogen (N) isotopic value in non lipid extracted (NLE) sample expressed in the delta (δ) notation | ‰ * NLE_C:N_ratio: Carbon (C) to nitrogen (N) elemental ratio in non lipid extracted (NLE) sample | None * LE_C%: Carbon (C) elemental concentration in lipid extracted (LE) sample as percentage of dry weight | % * LE_δ13C: Carbon (C) isotopic value in lipid extracted (LE) sample expressed in the delta (δ) notation | ‰ * LE_N%: Nitrogen (N) elemental concentration in lipid extracted (LE) sample as percentage of dry weight | % * LE_δ15N: Nitrogen (N) isotopic value in lipid extracted (LE) sample expressed in the delta (δ) notation | ‰ * LE_C:N_ratio: Carbon (C) to nitrogen (N) elemental ratio in lipid extracted (LE) sample | None * Notes: Sample collection and analysis notes | None ## Code/software Not applicable ## Access information Data was derived from the following sources: * Seghers et al. (In submission) Arithmetic normalization models for the effects of lipid on carbon stable isotope values in silver carp (Hypophthalmichthys molitrix) tissue