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Document Type

Thesis - University Access Only

Award Date

1998

Degree Name

Master of Science (MS)

Department / School

Wildlife and Fisheries Science

First Advisor

Michael L. Brown

Abstract

A decline in the walleye Stizostedion vitreum sport fishery in lower Lake Oahe, South Dakota, was documented in the early l 980's and has since been attributed to poor natural reproduction and/or recruitment. Contaminants are highly suspected in lower Lake Oahe because of the low natural reproduction/recruitment and the lower hatchability of eggs produced from broodstock walleyes. It has been documented that concentrations of dissolved selenium in the Cheyenne River have been higher than in other tributaries used for walleye broodstock collection the last 15 years. To determine whether selenium contributes to problems in the Lake Oahe walleye population, adult walleye were collected from three sites during spawning operations in April 1994, 1995, and 1996 to obtain tissue samples. Muscle, liver, and gonadal tissues were analyzed with a modified fluorometric method to determine selenium concentrations in fish. These tissues were also analyzed for mercury content using cold-vapor atomic absorption. No significant differences in tissue selenium concentrations among sites could be determined that would explain differential walleye egg hatchability. The same conclusion was reached with the mercury analysis. Interactions between the two elements have shown synergistic effects in common carp eggs, but no conclusions could be drawn from the data. Acute and chronic toxicity of chemicals to the aquatic environment is of great concern to aquatic life which depends upon the water to survive. Many species have been tested for the acute concentration of chemicals that will kill fifty percent of the test organisms within a 48-96 h time period. These LCSO tests often are dependent upon life stages of test organisms. Usually, early life stages of fish are more susceptible to chemicals than are older fish. Little chronic information is known for fish, especially the effects on reproduction. No information could be found for juvenile walleye exposed to sodium selenite over a 96-h period to determine what concentration might impact early life stages in a walleye population. A 96-h sodium selenite acute study using probit analysis determined that 1 1. 7 mg/L caused fifty percent mortality in juvenile walleye. Chronic toxicity might influence a species ability to survive in the environment more than acute toxicity because high concentrations are rarely found and will dilute over a large area. Therefore, juvenile walleyes were reared for 6 weeks on a diet supplemented with elevated selenium concentrations of up to 20 μgig. The walleyes incorporated the selenium in a short time period, then appeared to reach an equilibrium where the walleye disposed of the excess selenium. Growth and feed conversion during the selenium incorporation phase were monitored with no significant differences being observed, but this might have been influenced by the short incorporation phase of 6 weeks. Wall eye feeding behavior was evaluated to determine if elevated selenium might have an effect. Wall eyes with elevated selenium exhibited a significantly higher capture rate and capture efficiency of prey than control fish. No other feeding differences were detected. Genetic evaluations of the three walleye subpopulations of Lake Oahe from the Grand, Moreau, and Cheyenne rivers determined that the subpopulations were genetically similar. However, certain morphometric traits, such as head size, were detennined to be significantly different. Because certain traits differed among subpopulations, performance may differ as well. Therefore, experiments were conducted to evaluate walleye subpopulation performance characteristics under controlled conditions to detennine which progeny was more conducive to hatchery production. These performance characteristics include egg hatchability, survival, feed trainability, feed conversion, relative growth, and relative weight. In April 1995 and 1996, eggs from broodstock of the three walleye subpopulations were collected and transported to the Blue Dog State Fish Hatchery, Webster, South Dakota, where the resulting fry were stocked into ponds. Grand River walleyes produced the highest percent hatch for 1995 and 1996, (65.6% and 66. 8%, respectively) when compared to Cheyenne River walleyes (1995, 57.1 %; 1996, 43.1%) and Moreau River walleyes (1995, 44.5%; 1996, 52.6%). In June, fingerlings were collected from the ponds, transported to South Dakota State University and placed into a recirculating system where performance characteristics were monitored. All groups exhibited conversion to pelleted food after 1 1-d for both years. Survival 3 1 d after removal from ponds varied between years, depending upon condition at harvest from ponds. No differences {P>0.05) were found between subpopulations at the end of the experiments for relative growth, feed conversion, or relative weight (Wr) Based on these controlled trials, there did not seem to be performance differences among progeny from the three spawning sites. However, there did seem to be hatchability differences, with Grand River walleyes having the highest hatchability.

Library of Congress Subject Headings

Selenium -- Physiological effect
Walleye (Fish) -- Effect of chemicals on -- Oahe, Lake (S.D. and N.D.)

Description

Includes bibliographical references (page 79-92)

Format

application/pdf

Number of Pages

112

Publisher

South Dakota State University

Rights

Copyright © 1997 Robert J. Mauk. All rights reserved.

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