Dissertation (PhD (Agric))--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: A breeding programme aimed at the genetic improvement of growth rate of rainbow trout was initiated in
1988 by the Department of Genetics, University of Stellenbosch, in collaboration with the local trout
producer's organisations. The first phase of the breeding programme included the collection, evaluation and
selection of the best available genetic material from 13 different genetic groups (nine local and four
overseas) to make up two separate base populations as odd and even year-groups. This was done to
establishment a base population with high genetic merit and variation at the onset of the breeding
programme. Statistically significant and commercially valuable genetic differences in terms of weight and
length gain were detected between the various hatchery groups.
The next two generations of the breeding program included a series of single and double crosses in order to
increase the levels of genetic variation in the base populations, and to investigate possible heterosis and
specific and general combining ability among the crosses. Significant levels of heterosis (6.7% to 9.6%) and
general combining ability was found for weight and length gain during consecutive growth stages. No
evidence was found for specific combining ability among the crosses. The crossing of selected offspring
from the original genetic groups followed by the application of intensive multi-stage selection for growth
rate within progeny groups has led to the establishment of second and third generation parental populations
with higher levels of genetic variation and improved individual genetic merit with regard to growth rate. The
exploitation of non-additive genetic variation within the base populations through crossbreeding and
heterosis during the early stages of the selection programme was delayed in favour of the utilization of
additive genetic variance through a procedure of multi-stage selection that incorporated high intensities of
selection within and between family groups.
The estimation of genetic parameters during the fourth generation on the basis of a hierarchical half-sib
family structure confirmed the presence of high levels of additive genetic variation within the respective
populations/year-groups. High heritability values in the range of 0.40 to 0.53 were recorded for body weight
and length at 150 days. Genetic correlations between the traits were also high, in the range of 0.74 to 0.82.
The cumulative realized response of 50% in body length for the EVEN year-group after six generations of
selection (8.3% per generation), and the 33% for the ODD year-group after five generations of selection
(6.6% per generation) confirms the efficiency of the multi-stage selection procedure to exploit the available
additive genetic variation for growth rate within the respective populations.
The programme is still ongoing, entering its 7th generation in 2004 and is supplying about 50-60% of
commercial material through direct supplies of broodstock, ova and fingerlings and indirect supplies via
multiplier stations (commercial hatcheries). The programme was the first of its kind in relation to
aquaculture species in the Southern African region, and has since initiated the introduction of programmes of
genetic improvement in three other indigenous species, namely tilapia (Oreochromis mossambicus), African
catfish (Clarias gariepinus) and abalone (Haliotis midae). / AFRIKAANSE OPSOMMING: ‘n Teelprogram gerig op die verbetering van groeitempo in reënboogforel is in 1988 ingestel onder toesig van
die Departement Genetika aan die Universiteit van Stellenbosch, in sameweking met die plaaslike
forelprodusenteverenigings. Die eerste fase van die teelprogram behels die versameling, evalasie en seleksie
van die beste beskikbare genetiese materiaal vanuit, 13 verskillende genetiese groepe (nege plaaslike en vier
van oorsee) om twee basispopulasies te ontwikkel in elk van die gelyke en ongelyke jaargange. Die doel
daarvan was om ’n basispopulasie met hoë genetiese meriete en variasie te ontwikkel met die aanvang van die
teelprogram gerig op genetiese verbetering, deur middel van seleksie. Statisties betekenisvolle en ekonomies
belangrike genetiese verskille in massa- en lengtetoename is aangetref, tussen die onderskeie genetiese groepe.
Die daaropvolgende twee generasies binne die teelprogram behels die uitvoering van ’n reeks enkel- en
dubbelkruisings ten einde ’n verdere toename in genetiese variasie in die basispopulasies te bewerkstellig,
sowel as om die voorkoms van heterose en algemene, sowel as spesifieke kombinerings-vermoë tussen die
kruisings te bepaal. Betekenisvolle vlakke van heterose (6.7% tot 9.6%) sowel as algemene
kombineringsvermoë, is aangetref ten opsigte van massa- en lengtetoename in opeenvolgende groeifases. Daar
kon geen aanduiding van betekenisvolle, spesifieke kombineringsvermoë gevind word nie. Die kruising van
geselekteerde nageslag vanuit die oorspronklike genetiese groepe, gevolg deur ‘n multi-fase seleksiemetode vir
groeitempo binne nageslaggroepe, het bygedra tot die ontwikkeling van ‘n tweede en derde generasie
broeipopulasie wat beskik oor hoër vlakke van genetiese variasie en verbeterde individuele meriete ten opsigte
van groeitempo. Die benutting van nie-additatiewe genetiese variasie binne die basispopulasies deur middel
van kruisteling en heterose tydens die vroee stadium van die teelprogram is uitgestel ten gunste van die
benutting van additatiewe genetiese variasie deur middel van ‘n multi-fase seleksiemetode, wat berus het op
die toepassing van hoë vlakke van seleksie-intensteit binne en tussen familiegroepe.
Die beraming van genetiese parameters tydens die vierde generasie het die voorkoms van hoe vlakke van
additatiewe variasie binne die onderskeie jaargroepe bevestig. Hoë oorerflikhede van 0.40 tot 0.53 is beraam
vir ligaamsmassa en -lengte op die ouderdom van 150 dae. Genetiese korrelasies tussen die kenmerke was ook
hoog met waardes van 0.74 tot 0.82. Die saamgestelde gerealiseerde seleksierespons van 50% vir
liggaamslengte vir die “EVEN”-jaargroep na afloop van ses generasies van seleksie (8.3% per generasie) en
die 33% van die “ODD”-jaargroep na afloop van vyf generasies van seleksie (6.6% per generasie) het die
doeltreffendheid van die multi-fase seleksiemetode bevestig ten opsigte van die benutting van die additatiewe
variasie vir groeitempo binne die onderskeie basispopulasies/jaargroepe.
Die teelprogram duur steeds voort en sal die 7de generasie in 2004 bereik. Die program voorsien nagenoeg
50-60% van die kommersiele materiaal vanuit direkte voorsiening van teelmaterial, eiers en vingerlinge asook
die indirekte voorsiening via kommersiële teelstasies. Die teelprogram was die eerste van sy soort met
betrekking tot akwakultuurspesies in Suider Afrika en het bygedra tot die implimentering van programme van
genetiese verbetering in drie inheemse spesies, naamlik die tilapia (Oreochromis mossambicus), die baber
(Clarias gariepinus) en die perlemoen (Haliotis midae).
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/15937 |
| Date | 12 1900 |
| Creators | Brink, Daniel |
| Contributors | Louw, J. H., Hoffman, L. C., University of Stellenbosch. Faculty of AgriSciences. Dept. of Genetics. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xviii, 97 leaves : ill. |
| Rights | University of Stellenbosch |
Page generated in 0.0111 seconds