Hulata, G.         ARO                 Bet Dagan              Israel
Gall, G.A.E.       UC, Davis       Davis             CA   USA

Proposal Abstract

Production of tilapia is an important sector of aquaculture, both in the United States and Israel.  Tilapia culture in temperate climates is highly affected by species sensitivity to low temperatures.  Lack of freshwater is a chronic and continuing problem in the US, Israel, and many coastal areas of the world.  The genetic bases of cold tolerance has not been well investigated and previous attempts failed to realize response to selection for this trait within species, although species differ in their tolerance to cool temperatures.  In addition, some tilapia species exhibit tolerance to saline water, but only a few species of commercial importance can tolerate salinity over 15 ppt.  Genetic manipulation could produce new tilapia stocks for culture at low temperatures and in high salinity brackish water and marine systems, enabling their exploitation in tropical and arid coastal areas.

 Based on the ideas from plant breeding and the opportunities offered by molecular biology, a program was initiated in 1995 to develop genetically superior tilapia from a synthetic stock (ACO) produced by inter-crossing five groups of fish: Oreochromis niloticus [wild type (On) and red (ROn) strains], O. aureus (Oa), O. mossambicus (Om) and Sarotherodon galilaeus (Sg).  The project (funded by BARD 1996-1999) has made excellent progress.  Three-way (3WC) and four-way (4WC) crosses have been produced with all four species contributing to the ACO.  The (Om x Oa) x (Sg x On) 4WC has been bred for another generation and this genetically variable stock will serve as a base population for breed improvement.  A genomic map with 223 markers in 24 linkage groups has been produced, indicating good coverage of the 22 chromosome pairs.  A search for quantitative trait loci (QTL) targeting cold tolerance was initiated using F2 and 4WC families.  Preliminary genome scans identified a putative QTL for cold tolerance in association with a mapped microsatellite in the Om x Oa F2 and AFLP markers in the 4WC.

 The goal of the proposed research is to develop knowledge central to the genetic improvement of tilapia that will increase production volume and efficiency.  The heart of the proposal is a breeding program, to be conducted in Israel using individual and family performance with selection based on BLUP estimates of breeding values.  Two select lines will be established: one selected for cold tolerance and growth rate in freshwater and one selected for growth rate in seawater.  A small control line will be maintained for the purpose of detecting any major shifts in environmental conditions during the early generations of the selection program.  The program will also include estimation of genetic parameters using full- and half-sib families produced during the first generations of the breeding program.  Tissue samples will be preserved from all ancestors and performance tested fish, to allow monitoring of genetic markers for associations with performance traits, once selected lines have diverged.