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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-09

Staff
Auburn University, Alabama

Ronald P. PhelpsUS Principal Investigator
Robert CarpenterGraduate Research Assistant (USA; 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 a 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.

Work Plan Research

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

Note: Owing to delays, the scope of 9RCR6 was limited to 9RCR6A, Selection of individuals for sex inheritance characteristics for use in monosex production. Details of this change are documented in the Addendum to the Ninth Work Plan.

Conferences

Aquaculture America 2001 at Orlando, Florida, 21–25 January 2001. (Phelps)
PD/A CRSP Annual Meeting at Orlando, Florida, 26 January 2001. (Phelps)

Monosex Tilapia Production through Androgenesis: Selection of Individuals for Sex Inheritance Characteristics for Use in Monosex Production

Ninth Work Plan, Reproduction Control Research 6A (9RCR6A)
Final Report

Ronald P. Phelps and Robert H. Carpenter
Department of Fisheries and Allied Aquacultures
Auburn University, Alabama, USA

Abstract

Intraspecific breeding programs have been developed to exploit the sex inheritance mechanism in the tilapia Oreochromis niloticus to produce male populations. These programs are built on the premise that the mechanism of sex inheritance must conform closely to a monofactorial sex determination with a heterogametic male. Sex inheritance in tilapia, however, appears to be more complicated. The sex ratio of an individual spawn often does not conform to the expected 1:1 ratio. A better understanding of sex inheritance in tilapia and the identification of tilapia populations with a minimum variation in progeny sex ratios from individual spawns is needed for a successful intraspecific breeding program to produce male tilapia.

Nine families of O. niloticus, each from individual pair spawns, were selected based on the sex ratio in the family. Two families were highly skewed to male (100% male), three were near 50% male, and four were skewed to female. Fish within the same family were mated, and the sex ratios of the progeny were determined. In the two families that were all males, the males were mated to females from a family with a sex ratio near 1:1. Ten sets of progeny per family were sexed with the exception of one family, from which only eight sets were available.

Sex ratios did not appear to be passed on from one generation to another in the fish used in our study. A realized heritability for sex ratio of –0.09 was calculated. No family with skewed sex ratios produced progeny from sibling matings with similarly skewed sex ratios. Family VIII, which had a 1:1 male:female ratio, had a range of 43 to 68% male in its sets of progeny. Family V, which was 22% male, gave 10 sets of progeny, of which five sets were > 70% male. Families II and VII, which were 100% male, when crossed with females from Family III gave sets of progeny ranging from 23 to 79% male. When the percentage of males in the female parent family (III, 40% male) was considered in matings with Families II and VII, 40 and 50% of the spawns, respectively, differed in sex ratios from the female parent family.


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