AUTHORS: Justin Sturtz, South Dakota State University; Benjamin J. Schall, South Dakota Department of Game, Fish and Parks; Matthew J. Ward, South Dakota Department of Game, Fish and Parks; Cody E. Treft, South Dakota Department of Game, Fish and Parks; Christopher Cheek, South Dakota State University
ABSTRACT: Determining the natal origins of fish can provide critical information for fisheries management and conservation efforts. Recirculating Aquaculture Systems (RAS) are advanced, fish-rearing setups that filter and recycle water within the system, significantly reducing the need for fresh water and allowing for high-density rearing of fish under efficient growth conditions. In contrast, traditional fish stocking often involves rearing fish in raceways or outdoor ponds. Differences in forage between RAS (pellet-fed) and pond (natural forage) reared fish may result in unique isotopic signatures in the fish tissue. Historically archived isotope signatures in fish eye lenses may be useful in differentiating rearing sources, providing an additional tool for delineating stock contribution. This study investigates the feasibility of using isotopic composition of fish eye lenses to discern the known rearing environment (RAS vs. pond vs. wild) of fall, advanced fingerling age-0 Walleye (Sander vitreus). We collected 10 RAS-reared, pellet-fed walleye from Cleghorn fish hatchery in Rapid City SD (mean = 159mm), 10 pond-reared natural source-fed walleye from Blue Dog hatchery in Waubay SD (mean = 179mm), and 10 wild- caught walleye from Clear Lake in Sioux Falls SD (mean = 170mm). Eye lens layers were delaminated to remove ~300 µm for each layer, resulting in 3 to 4 layers per fish including the core. Eye lens layers were sent for carbon (δ13C) and nitrogen (δ15N) isotope analysis, and whole eye lenses from the second eye were sent for δ13C, δ15N, and sulfur (δ34S) analysis. Preliminary δ13C and δ15N results illustrated unique signatures among stocking sources, high signature precision for the pellet-fed RAS fish, and shifting signatures with known changes in diet for pond-reared fish. The results of this study could be used by managers who are focusing on identifying the stock contribution of RAS and pond-reared fishes.
