Date of Award

Fall 2008

Project Type

Thesis

Program or Major

Zoology

Degree Name

Master of Science

Abstract

In many cultured finfish species, sexually dimorphic growth is observed, therefore, understanding the mechanisms of differentiation in fishes is necessary for successful aquaculture. Summer flounder (Paralichthys dentatus ) and black sea bass (Centropristis striata) are good candidate species for aquaculture because they easily adapt to culture conditions and have high market value. The production of monosex populations is advantageous in species exhibiting sexually dimorphic growth rates. The purpose of this research was to gain an understanding of the mechanisms involved in sex differentiation of summer flounder and black sea bass. In summer flounder, monosex female culture is beneficial because females grow two to three times larger than males. Like many teleosts with an XX/XY sex chromosome system, Paralichthid females are homogametic (XX) and males heterogametic (XY). Only homogametic individuals can be phenotypically sex reversed during sex differentiation. In the first part of this study, meiogynogenesis and temperature-dependent sex determination were used in the first steps towards the production of monosex female cultures of summer flounder. Meiogynogens were produced by applying a 6 minute pressure shock (8,500 psi) 2 minutes post-fertilization resulting in the production of 1,100 juveniles. For temperature-dependent sex determination, meiogynogens and control diploids were reared at a low temperature regime (12-20°C), 21, and 26°C for 376 days post hatch (DPH). Females were primarily produced at the low temperature regime (62.5% in meiogynogens and 22.6% in controls). The second part of this study examined the disruption of female-specific sex differentiation in black sea bass. Metamorphosed juveniles were reared at 17, 21, and 25°C for 279 DPH. While there was not a significant difference in sex ratios among treatments, the expected outcome of 100% female was not obtained in this protogynous species. Additionally, males were significantly larger than females by 275 DPH. This may provide a mechanism for future production of monosex (male) populations of this protogynous species. Understanding the control of sex in this species is crucial for broodstock maintenance. This research will increase our understanding of the reproductive biology of these species and improve their culture.

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