within density classes, between three and 13 replicates were available for the analysis of growth performance data. Differences in mean body weights between clones and
controls kept among the three different density classes were evaluated by ANOVA, Ž
. applying The Generalised Linear Models GLM procedure on the following statistical
model:
U U
Y s m q G q C q G C
q T G C
q e
Ž .
Ž .
i j i j
i jk l i
j k
i jk l
where Y s value observed in the ijklth fish; m s overall mean, G s effect of the ith
i jk l i
Ž genetic category i s 1, 2; 1 s homozygous isogenic groups; 2 s all-female heterozy-
. Ž
gous control groups ; C s effect of the jth density class j s 1, 2, 3; 1 s one to 20 fish
j
. Ž .
per tank; 2 s 21 to 50 fish per tank; 3 s 51 to 80 fish per tank ; GC s effect of the
i j
wŽ . x
interaction between the ith genetic category and the jth density class; T GC
s
k i j
random effect of the k th tank within the ith genetic category and the jth density class; and e
s error term.
i jk l
To prove the effect of the genetic category for its significance the G -term was tested
i
wŽ . x
against the T GC
-term in an F-test.
k i j
Differences in variances of body weight observed between clonal- and control groups were analysed using F-tests from pooled within tank variances.
3. Results
Of 77 adult homozygous females derived by induction of a mitotic gynogenesis, only Ž
. Ž
10 females 13 produced eggs that developed Muller-Belecke and Horstgen-Schwark,
¨ ¨
. 1995 . Adult first generation clonal fish were derived from meiotic gynogenetic repro-
duction of six mitotic gynogenetic females as shown in Table 1. Mothers of the Clones II to VI descended from the same clone grandmother. The clonal genotypes were free
from recessive lethal genes as shown by the viability of the clone mothers, which on basis on their mitotic gynogenetic origin were completely homozygous. However,
survival rates within clones were extremely low when compared with survival rates of
Ž .
untreated offspring from normal heterozygous females Table 1 . Considerable differ- Ž
ences were observed between the clones e.g., 16.2 first feeding fry in Clone II vs. .
1.46 in Clone VI . The clonal status was confirmed by screening genetic markers for all the 343 adult fish that were derived in the first generation of clone production.
The reproductive traits of the first generation clonal fish, important for the continua- Ž
. tion of the clonal lines, were also on a low level Table 2 . Only 44 of the egg batches
that were derived from first generation clonal females showed first feeding fry in untreated control groups. The corresponding parameter in untreated egg batches from
Ž .
normal heterozygous females was 81 data not shown . The reduced quality of eggs received from first generation clonal spawners was manifested by the low survival rates
of untreated groups. The survival rates observed in gynogenetically reproduced eggs Ž
. from first generation clonal females Table 2 ranged at approximately same level as
Ž was observed during the development of the first generation clones themselves Table
. 1 . Survival rates of different egg batches from different first generation clonal females
Ž .
within clones varied highly Table 2 . As demonstrated by genetic markers all the 494
adult fish that were produced by meiotic gynogenetic reproduction of first generation clonal females were also clonal.
Table 3 presents body weight data recorded from first and second generation clonal groups and corresponding all-female control groups, after finishing the above-described
standard performance testing. Calculated over all density classes, clonal groups showed reduced body weights in comparison with control groups. However, this difference was
not significant. The variability of body weight was significantly lower in clonal groups than in controls. As would be expected, the body weight of both, clonal and control
groups, decreased when the fish were kept under high densities. The variability of body weight was highest in control groups when they were kept in low density and decreased
to a comparable level in middle and high density classes. In clonal groups, however, the variability of body weight was comparable among the density classes, with some
tendency to increase if they were kept under the highest density. In some cases, considerable differences in body weights and in the variability of body weight were
observed within the clones when the clonal groups were kept under different density classes. The mean survival rate during the standard performance testing between 24th
and 136th day of life was 72.2 in all-female clonal groups and 70.5 in all-female
Ž .
heterozygous control groups data not shown . Mortality was almost evenly distributed with a slight tendency to increase from the 80th day of life on in clones as well as in
controls. Differences in mortality between the three density classes were not significant.
4. Discussion and conclusions
