Stable isotope analysis
Immediately following the behavioral experiment all fish were euthanized
with an overdose of phenoxyethanol. Fin and muscle samples were rinsed
with deionized water and cleaned by carefully removing any skin or bone
from the muscle samples. Samples were then dried at 55°C until fully
dry. Elemental analysis-isotope ratio mass spectrometry was used for the
carbon and nitrogen isotope analysis by the company Iso-Analytical
(https://www.iso-analytical.co.uk/) using their standard quality control
methods. The reference material used for both δ15N and
δ13C was soy protein (IA-R068). The analysis was
completed in batches, with the reference sample tested between each
batch. Stable isotope analysis was repeated for every sixth sample.
Repeat values all fell within a 0.20‰ range and the standard deviations
of repeated analyses of the reference materials was less than 0.10‰. All
values were within 0.10‰ of their certified values for
δ15N and δ13C indicating both good
precision and accuracy. The quality control samples used were soy
(IA-R068), L-alanine (IA-R038) and tuna protein (IA-R046). All control
samples were calibrated against international comparison standards
distributed by the International Atomic Energy Agency.