Using eye lens stable isotopes to identify the rearing origin of fall age-0 walleye (Sander vitreus)

Isotope values in fish eye lenses may be useful in differentiating rearing origins. We compared eye lens isotopic values of fall fingerling age-0 walleye (Sander vitreus) reared in a hatchery pond, a recirculating aquaculture system (RAS), and a natural lake. Using 10 fish per rearing source, we delaminated layers from one eye lens per fish to assess temporal changes in carbon (δ¹³C) and nitrogen (δ¹⁵N) and pulverized the whole second eye lens for δ¹³C, δ¹⁵N, and sulfur (δ³⁴S). RAS-reared walleye values exhibited high precision among individuals and were δ³⁴S enriched. Pond-reared walleye had lower δ¹³C and δ¹⁵N core values compared to other rearing sources. For δ¹³C and δ¹⁵N, values remained consistent among layers for RAS-reared walleye, δ¹⁵N slightly increased for pond-reared and lake-reared walleye, and δ¹³C increased substantially among subsequent layers in pond-reared walleye. Bayesian 95% ellipses did not overlap among rearing sources. These results demonstrate that eye lens stable isotope analysis may be a useful tool for differentiating hatchery-reared and wild large fingerling walleye, specifically from RAS- and pond-reared sources.