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Aquaculture 184 2000 67–76 www.elsevier.nlrlocateraqua-online
Performance testing of clonal Oreochromis niloticus lines
Andreas Muller-Belecke , Gabriele Horstgen-Schwark
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Institut fur Tierzucht und Haustiergenetik, UniÕersitat Gottingen, Albrecht-Thaer-Weg 3,
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D-37075 Gottingen, Germany
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Accepted 7 September 1999
Abstract
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Six different homozygous clonal lines 343 adult fish
were established by gynogenetic reproduction of mitotic gynogenetic Oreochromis niloticus females. Second generation clones
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494 adult fish were obtained by gynogenetic reproduction of clonal females. The clonal status of the fish was proven by the alloenzyme adenosine deaminase and DNA fingerprints. Performance
testing of the all-female clonal groups was carried out in comparison with adequate heterozygous control groups. Up to first feeding, clones showed a significantly reduced mean survival rate
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4.0 if compared with offspring of normal heterozygous fish 43.9 . Reproductive traits of the second generation clones varied between and within clonal lines. Mean body weight differences at
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136th day of life between all-female clonal groups 45.5 g , kept under three different density Ž
. classes, and corresponding all-female heterozygous control groups 50.2 g were not significant.
Ž Variation of body weight was significantly lower in all-female homozygous clones coefficient of
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. variation: 23.1 than in all-female heterozygous controls coefficient of variation: 34.1 .
Possible reasons for phenotypic variation between isogenic O. niloticus individuals are discussed. q
2000 Elsevier Science B.V. All rights reserved.
Keywords: Oreochromis niloticus; Gynogenesis; Clones; Survival; Growth
1. Introduction
Since the beginning of the 1930s, plant breeders succeeded in developing highly Ž
. productive seeds by crossing homozygous lines Allard, 1960 . Due to the heterozygous
isogenic status, the variability of performance traits was reduced in these crosses.
Corresponding author. 0044-8486r00r - see front matter q 2000 Elsevier Science B.V. All rights reserved.
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PII: S 0 0 4 4 - 8 4 8 6 9 9 0 0 3 1 8 - X
Furthermore, in some diallel crosses with clonal lines, high heterosis effects were found. Whether a breeding strategy including clone crosses is relevant for practical applications
depends on the performance of the clone crosses as well as the cost-effectiveness of development and maintenance of the clonal lines.
Until now, experiments to produce highly inbred lines of farm animals such as pig and poultry were not very successful. The relatively low increase in the inbreeding level
per generation and high losses of lines due to inbreeding depression made the practical Ž
. application of this strategy too expensive Ameli, 1989; Glodek, 1992 .
In fish, external fertilization and embryonic development allow the development of homozygous clones in only two generations by use of induced gynogenetic or androge-
Ž netic reproduction Thorgaard, 1986; Horstgen-Schwark, 1991; Horvath and Orban,
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. 1995 . The high fecundity of fish increases the probability of development of homozy-
gous genotypes free from expression of harmful genes and, therefore, viable and reproductively competent.
Ž Although clones have been developed within eight fish species Brachydanio rerio:
Streisinger et al., 1981; Oryzias latipes: Naruse et al., 1985; Cyprinus carpio: Komen et al., 1991; Plectoglossus altiÕelis: Han et al., 1991; Paralichtys oliÕaceus: Hara et al.,
1993; Oncorhynchus rhodurus: Kobayashi et al., 1994; Onchorhynchus mykiss: Young .
et al., 1995; Oreochromis niloticus: Muller-Belecke and Horstgen-Schwark, 1995 , only
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few data of their reproductive and growth performance in comparison to normal heterozygous controls have been published. The aim of the present investigation is to
supply performance data during the development, maintenance and reproduction of O. niloticus clones for subsequent evaluation of clone crosses.
2. Materials and methods
