Date of Award
August 2024
Degree Type
Thesis
Degree Name
Master of Science
Department
Freshwater Sciences and Technology
First Advisor
Dong Fang DFD Deng
Committee Members
Harvey HB Bootsma, Loadong LG Guo
Keywords
Aquaculture, Carbohydrate, Feeding Rate, Lipid, Stocking, Walleye
Abstract
Walleye (Sander vitreus) is an ecologically important and highly prized food fish in the Midwest region. With increasing commercial harvesting of wild walleye, more walleye are being stocked into the Great Lakes through aquaculture conservation and raised for production in aquaculture businesses. For aquaculture businesses and conservation, the feed can cost more than 50% of the entire operation’s total costs. Developing a profitable walleye aquaculture industry is crucial to meet the ever-growing market demand. This study aims to establish a cost-effective feeding strategy and formulate a nutritionally balanced feed to enhance walleye aquaculture. Two feeding trials were conducted on walleye with an initial body weight of 37 ± 1 g (n=30) within a flow-through water system (21 – 23 °C). In the first trial, walleye were subjected to four feeding rates (0.8%, 1.6%, 2.4%, and 4.0% of body weight per day) for 6 weeks to determine the optimal feeding rate (OFR). The feed was a commercial diet, consisting of 42% protein, 16% lipids, and 13.6% starch. The second feeding trial lasted for 9 weeks and aimed to assess the response of walleye to various diets formulated with different lipid-to-starch ratios: 0.50, 0.65, 0.83, 1.06, and 1.36. The dietary lipids ranged between 11% to 19%, while the dietary starch levels ranged between 14% to 22%. The protein content was consistent across all diets at 46.6%. Each treatment consisted of three replicates with 20 fish per replication. The walleye were fed four times daily (9:00 a.m., 12:00 p.m., 3:00 p.m., and 6:00 p.m.) using automatic feeders. At the end of each feeding trial, samples for both growth data and proximate composition were taken. The fish were subjected to acuate hypoxia (< 2 mg/L) and heat shock (increased from 23°C to 31°C) to address stress tolerance. We applied polynomial regression to estimate the optimal feeding rate and the ideal dietary lipid-carbohydrate combination based on growth performance, nutrient retention, and stress responses. The results revealed significant increases in fish growth, hepatosomatic index, visceral fat index, condition factor, feed conversion ratio, and whole fish lipid content with higher feeding rates (p < 0.05). Nutrient retention was also significantly impacted by the treatments. The optimal feeding rate was determined to be 3.51% based on weight gain, whereas a feeding rate of 1.35% was optimal for achieving the lowest feed conversion ratio. Additionally, the highest protein retention occurred at a 2.5% feeding rate, while 2.0% was optimal for energy retention. Both hypoxia and the heat shock resulted in increased glucose levels with higher feeding rates although no mortality was observed during the stress tests related to dietary treatments. Therefore, we recommended an optimal feeding rate between 2% and 2.5% of body weight per day based on growth and nutrient retention. A lower feeding rate (1.35%) can be considered to minimum feed cost. Under current conditions, a feeding rate of 0.8% provides sufficient nutrients for walleye maintenance. In the second feeding trial, no significant differences were observed in growth, morphology, or nutrient contents of whole fish, except for an increase in whole fish lipid content with higher lipid-to- starch in the test diets. Polynomial regression analysis indicated that a lipid-to-starch ratio of 0.98 resulted in the highest weight gain while a ratio of 1.05 achieved the lowest FCR. The highest protein retention and energy retention were observed at ratios of 0.67 and 0.79, respectively. Hypoxia and heat shock did not significantly affect serum glucose across dietary treatments, though mortality tended to be higher in the group fed a diet with a lipid-to-starch ratio of 1.36 (19% lipid and 14% starch). Based on growth performance and nutrient retention, the optimal ratio of lipids to carbohydrates for walleye feed is between 0.8 and 1.0, with lipids between 15% to 17% and starch between 16% to 18%. These findings provide valuable insights into nutrient requirements and aid in the development of cost-effective feeds for walleye farming. In conclusion, this study provides critical baseline data for effective feed management in walleye aquaculture, ultimately promoting sustainable development.
Recommended Citation
Gregory, Alexander, "ENHANCING THE AQUACULTURE POTENTIAL AND STOCKING OF WALLEYE (SANDER VITREUS) THROUGH MANAGEMENT OF FEED NUTRITION" (2024). Theses and Dissertations. 3574.
https://dc.uwm.edu/etd/3574