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Reproduction Control Research
PD/A CRSP Nineteenth Annual Administrative Report

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Research Projects
Reproduction Control Research

Subcontract No. RD010A-02

Staff
University of Oklahoma, Norman, Oklahoma

William Shelton US Principal Investigator
William BakerGraduate Student (USA; through August 2000; CRSP funded)

Background

Limited knowledge of the reproductive physiology and breeding of culture species was identified as one of the key constraints to aquaculture in the Continuation Plan 1996. Specifically, effective and practical control of reproduction is the major constraint in tilapia culture. Inter- and intraspecific breeding programs can result in populations with highly skewed sex ratios but often give inconsistent results. Interspecific crosses have not proven to be practical due to difficulties in maintaining the parent species integrity.

Intraspecific breeding programs have been developed to exploit the sex inheritance mechanism in Nile tilapia, Oreochromis niloticus. The androgenetic approach to developing YY males simplifies the identification of YY males, as all males produced should be of the YY genotype. Ninth Work Plan research sought a phenotypic marker to further simplify identification of YY males and continues efforts to develop androgenesis techniques for Nile tilapia of the Egyptian and Ghanaian strains.

Work Plan Research

The following Ninth Work Plan investigation continued into the current reporting period:

Note: 9RCR7 was terminated. The decision to terminate 9RCR7 is documented in the Addendum to the Ninth Work Plan.

Conference

PD/A CRSP Annual Meeting at Orlando, Florida, 26 January 2001. (Shelton)

Monosex Tilapia Production through Androgenesis

Ninth Work Plan, Reproduction Control Research 7 (9RCR7)
Final Report

William L. Shelton
University of Oklahoma
Norman, Oklahoma, USA

Abstract

Control of reproduction is vital to aquaculture and includes artificial propagation as well as management of unwanted recruitment. Developments in manipulation of the reproductive system provide options to enhance production. Nile tilapia, Oreochromis niloticus, spawning was managed by photoperiod and temperature manipulation. A controlled light cycle of 20L:4D and water temperature of 26 ± 2°C directed spawning to a predictable time frame. A developmental rate (t0) relationship was described and applied to chromosome manipulation. Blond Nile tilapia are homozygous recessive for a color mutation that was used as a phenotypic marker in the development of protocol for androgenetic induction, while the color pigmentation for red Nile tilapia is dominant over the wild type color pattern. Androgenotes were produced by neutralizing the female genome of normal color Nile tilapia or that of Red tilapia (600 J m-2 UV dose), eggs were activated with sperm from blond males or Ghana males, respectively, and then the eggs were diploidized with cold shock (11 ± 0.5°C for 60 min) applied at various times after incubation at 28 ± 0.2°C. Shock applied at 69 min post-activation produced greater numbers of androgenotes than shocks applied at 59 or 79 min post-activation; the shock application time of 69 min was used for induction with red tilapia stocks. Production of viable diploid androgenotes for crosses involving either red or blond and Ghana stocks was very low, and no progeny survived to maturity. Thus, neither verification of sex determination in androgenotes nor testing of monosex breeding was accomplished.

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