Lipid extraction alters amino acid composition and bulk, but not amino acid, carbon and nitrogen isotope values

Rationale: Concerns exist over observed shifts in value and variance of nitrogen isotopes following physicochemical extraction of lipids from organic matter. The mechanisms behind these apparent changes in bulk tissue δ15N values are not fully understood yet have major implications for analytical costs and integrity of data interpretations.
Methods: Changes in proximate analysis, amino acid composition, C:N ratios, bulk tissue and amino acid δ13C and δ15N values, and resulting isotope‐based food web metrics were compared between lipid‐intact and lipid‐extracted muscle tissue of fishes spanning <1% to >20% muscle fat content to identify mechanisms of nitrogen isotope fractionation associated with physicochemical lipid extraction.
Results: Bulk δ13C and δ15N values increased and %N, C:N ratios and crude protein content decreased following lipid extraction. Resulting bulk isotope niche spacing and overlap varied significantly between lipid‐intact and lipid‐extracted tissues. While am..., Four species of marine fishes with varying levels of muscle total lipid content (Table 1) were purchased from Rhode Island fish markets: wild-caught Atlantic cod (Gadus morhua, hereafter “cod”) from southern George’s Bank, wild-caught bluefish (Pomatomus saltatrix, hereafter “bluefish”) from southern George’s Bank, wild-caught Atlantic herring (Clupea harengus, hereafter “herring”) from “the Northwest Atlantic”, and Norwegian farmed “organic” Atlantic salmon (Salmo salar, hereafter “salmon”). Dorsal muscle tissue was isolated from each fish fillet, frozen at -20 °C, and then lyophilized for 72 hrs prior to homogenization with mortar and pestle. Freeze-dried, homogenized samples were subdivided into two aliquots, one with original lipid content intact and one with lipids extracted. For the latter, lipids were removed using a modified version of the classic Bligh and Dyer method. Briefly, freeze-dried, homogenized samples were soaked for 30 min at room temperature in a chloroform:methanol..., , # Lipid extraction alters amino acid composition and bulk, but not amino acid, carbon and nitrogen isotope values

[https://doi.org/10.5061/dryad.18931zd4x](https://doi.org/10.5061/dryad.18931zd4x)

## Description of the data and file structure

Individual fish data including: common name, Genus species, treatment (lipid intact, lipid extracted), sample ID, percent carbon, percent nitrogen, C:N ratio, crude protein, crude fat, carbohydrates, fiber, ash, and moisture content, amino acid composition (relative %), bulk d13C values, bulk d15N values, total hydrolysable amino acid (THAA) d13C values, THAA d15N values, individual essential amino acid d13C values (mean and SD from triplicate analyses, N = non-essential amino acids, E = essential amino acids) with lipids intact and with lipids extracted, individual amino acid d15N values (mean and SD from triplicate analyses, T = trophic amino acid, S = source amino acid, M = metabolic amino acid) amino acid carbon isotope fingerprinting model ...