Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Wildlife and Fisheries Science

First Advisor

Charles G. Scalet


In September 1986, approximately 50,000 rainbow trout (Salmo gairdneri) eggs were fertilized and subjected to heat shocks to prevent expulsion of the second polar body, theoretically resulting in triploid embryos. Heat shocks were at 26 and 28°c, began 10, 20, 30, or 40 min after fertilization, and lasted for 10 or 20 min for a total of 16 treatments. Another 25,000 eggs served as controls and were handled identically but at a normal water temperature of 12°c. Cumulative hatching rates for eggs that were heat-shocked at 26 and 28° were 64 and 50%, respectively, compared to control eggs which had a cumulative hatching rate of 76%. At age 7 months 25 fish from each treatment group were individually evaluated for ploidy level by quantifying DNA content of red blood cells using flow cytometry. Rates of triploidy induction ranged from 0-100%, and all variables (temperature, time after fertilization when heat shock began, and duration of heat shock) significantly (p ≤.01} affected triploid yield. The most successful treatment under the conditions of this experiment was at 28°c beginning 20 min after fertilization for a duration of 10 min, which resulted in 60. 5% survival to feeding and 100% triploidy induction. Four treatment groups containing the highest percentage of triploids (92-100%), along with an equal number of control diploids, were retained for stocking and further evaluation. Diploid and triploid fish were fin clipped and stocked in equal proportions into six small (l.0 - 2.5 hectare impoundments in south-central South Dakota. The relative survival and growth of diploid and triploid fish in a wild situation will be monitored over the next several years. This will allow an assessment of triploid rainbow trout as a fisheries management option in South Dakota.

Library of Congress Subject Headings

Rainbow trout -- Reproduction
Fishery management -- South Dakota


Includes bibliographical references (pages 52-60)



Number of Pages



South Dakota State University


No Copyright - Non-Commercial Use Only