Identifier

etd-07142005-134611

Degree

Master of Science (MS)

Department

Renewable Natural Resources

Document Type

Thesis

Abstract

Declines in annual oyster landings and problems associated with seasonal reduction of oyster meat yields have increased interest for development of techniques to produce oysters with enhanced growth characteristics. Research interest has been focused on developing improved lines by induction of polyploidy. The goal of the present study was to evaluate the enhancement of gonadal development of triploid oysters, by the use of the hormone estradiol 17-â (E2) to produce viable eggs for the development of tetraploid broodstocks. Previous studies with the Pacific oyster, Crassostrea gigas, have shown: (1) the need to use the larger eggs of triploid females to accommodate a tetraploid nucleus, and (2) that E2 appears to be responsible for ovarian maturation. The objective of this research was to compare the effect of three dosages of E2 (0.0, 37.5, 75.0 ng/g wet weight) on ovarian maturation of diploid and triploid eastern oysters, Crassostrea virginica, by measuring: 1) gonad-to-body ratio; 2) oocyte area; 3) levels of E2 in the hemolymph; and, 4) by qualitatively staging gonadal development. Experiments were performed in August of 2003 and May and August of 2004 for 9, 12, and 15 days. Image analysis of histological sections (gonadal condition) and enzyme immunoassays (E2 levels) were used to evaluate the effects of steroidal treatments. There was no evidence of oysters in spawning condition in any of the control groups of the triploid oysters, yet oysters in spawning condition were found in the low and high dose treatments in percentages as high as 40%. For the diploid oysters, the effect of E2 was less apparent due to their natural state of fecundity during the summer months. Concentrations of E2 were measured in diploid and triploid oysters and their levels fluctuated from 13.8 to 29.1 for diploids and from 16 to 33.8 for diploids, with respect to the stage of gonadal maturation. The overall response of triploid oysters to E2 suggested that this hormone had a positive effect on ovarian maturation. These results can have direct applicability for the development of tetraploid broodstocks in the eastern oyster.

Date

2005

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Terrence R Tiersch

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