Recipient Organization
NORTH CAROLINA STATE UNIV
(N/A)
RALEIGH,NC 27695
Performing Department
Biology
Non Technical Summary
Key to advancing the profitability and culture potential of Southern flounder is the reliable production of faster growing stocks consisting only of females. Females grow 2-3 times faster and have larger maximum sizes than males. The purpose of this project is to promote production of only faster-growing all-female populations of flounder through identification of those environmental parameters that regulate and mechanisms that mediate sex determination processes.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
Key to advancing the profitability and culture potential of Southern flounder is the reliable production of faster growing stocks consisting only of females. Females grow 2-3 times faster and have larger maximum sizes than males. Our pilot scale studies show that the estimated breakeven costs for growing all-female populations of southern flounder is 35% less than that of mixed sex populations. Southern flounder show environmentally sensitive sex determination wherein only the XX female genotype is susceptible to sex reversal during early development. We have found that temperature, but not salinity or light intensity, can dramatically skew sex ratios with higher and lower temperatures favoring development of slower-growing males. Our preliminary work also shows that tank color (i.e., the background for the bottom dwelling flounder) also may lead to overproduction of males, despite rearing at optimal temperatures for female development. Therefore, our goals will be to identify those tank colors and stocking densities that limit sex reversal and maximize the production of females. We will also test whether the "stress" hormone cortisol might be the physiological mediator of the sex determination responses elicited by environmental parameters that cause sex reversal of southern flounder.
Project Methods
Our initial work with mixed sex flounder populations showed that blue tank color yields significantly higher proportions of male fish even at a 23C rearing temperature that maximizes the female phenotype, suggesting tank color regulates sex determination. Five different tank colors (yellow, green, red, blue and grey), representative of different areas of a CIE LAB color space and within the color response sensitivity of flounder, will be tested for sex determining effects using genetic all female flounder stocks. Gonadal gene expression of aromatase, FoxL2 and mullerian-inhibiting hormone and histological examination of gonads will be used to assess the sex of fish grown under different background colors. Subsamples of fish will also be taken at intervals to assess whole body levels of the stress hormone, cortisol, which we postulate mediates the effects of tank color on male sex differentiation. Additional studies will assess potential effects of stocking density on sex determination in flounder and that which best promotes development of the faster growing female phenotype.