Ž .
variance Sokal and Rolf, 1981 in the statistical software package,
STATGRAPHICS
, Ž
. version 5 Statistical Graphics, Rockville, MD .
2.3.2. Growing method and leÕel on diploid and triploid S. glomerata at Merimbula All data were analysed using multiple ANOVA in the Statgraphics package above.
For the measurements on samples of spat taken at the start of the experiment, homogeneity of variances was confirmed for shell height for triploids and diploids using
Ž .
Cochran’s test C s 0.507, P 0.05 . Weights were log transformed to satisfy require- Ž
. ments for homogeneity C s 0.501, P 0.05 .
Ž Weight data were expressed as weight increase, final mean whole weight for each
.
0.5
replicate-initial mean weight . Percentage mortality data were arcsin x transformed.
Ž Homogeneity was confirmed for shell height and whole weight C s 0.354, C s 0.256,
. respectively: P 0.05 . Mortalities remained slightly heterogeneous following transfor-
Ž .
mation C s 0.467, P s 0.029 . This is, however, a minor departure from homogeneity Ž
. and ANOVA is sufficiently robust to overcome such departures Underwood, 1981 .
3. Results
3.1. Mortality leÕels at fiÕe growing leÕels on the Georges RiÕer At the termination of the experiment, an inverse relationship was apparent between
Ž .
cumulative mortality levels and growing level Table 1, Fig. 1 . The mean cumulative Ž
. Ž
. mortality level of oysters at the highest level 9.3 was significantly lower P - 0.05
Ž .
than at normal tray level 35.1 and this in turn was significantly lower than at the Ž
. lowest growing level 52.4 . Mortalities at intermediate growing levels were consistent
with this trend after the August count when a sharp increase in mortalities was recorded Ž
. for all but the highest growing level Fig. 1 .
Measurements of whole weight, dry meat condition index and glycogen content were Ž
. not significantly different between the growing level treatments
P 0.05, Table 1 .
Table 1 Effect of growing level on the physiology and mortality levels of Sydney rock oysters S. glomerata
Growing level September 1986
Whole Condition
Glycogen Cumulative
Cumulative
U U
U
Ž . Ž
. Ž .
Ž . weight g
index gr100 g dry meat
mortalities mortalities
UU UU
to Sept. 1986 to Jan. 1987
a a
a a
a
q300 mm 43.32.3
12.031.2 22.160.92
5.71.2 9.30.9
a a
a a
a
q150 mm 56.110.4
13.441.0 22.970.63
7.42.2 16.84.2
a a
a a,b
b
0 mm 56.33.0
12.441.1 23.101.87
11.81.3 35.18.4
a a
a b,c
b,c
y150 mm 57.95.8
12.750.8 22.070.66
21.49.1 47.29.6
a a
a c
c
y300 mm 54.54.4
12.551.2 22.400.41
25.55.4 52.46.2
U
Data are expressed as meanSD. Within columns, means, which do not have a common superscript, Ž
. differ significantly P - 0.05 .
UU
For analysis of variance an arcsin x
0.5
transformation was used and Tukey’s test was used to compare mean values.
Ž . Fig. 1. The effect of deviation of standard growing height on cumulative mortality levels of the Sydney
rock oyster S. glomerata in Woolooware Bay, NSW from April 1986 to January 1987.
Data for the five growing levels were pooled for dry meat condition index and for glycogen content to reveal overall trends, which followed the usual seasonal pattern
Ž .
Ž .
Nell et al., 1994 . These parameters are tabulated for the September sampling Table 1 at the time when mortalities were rapidly increasing, and showed no aberrations that
might be associated with the mortalities. 3.2. Growing method and leÕel on diploid and triploid S. glomerata at Merimbula
The April 1995 visit revealed losses of oysters from the high level diploid stick, and the high level triploid stick treatments. The leaseholder reported pelicans roosting as the
cause. Numbers at termination were markedly reduced for these treatments.
Table 2 The proportion of Sydney rock oysters S. glomerata infested with the winter mortality parasite M. roughleyi at
Merimbula Lake, NSW These trials began on June, 1994.
Date of examination Treatment
Number Number
Proportion Ž
. Ž .
Ploidyrculturerheight examined
infested infested
June 1996 TriploidrTrayrLow
30 DiploidrTrayrLow
30 Oct. 1996
TriploidrTrayrHigh 20
6 30
TriploidrTrayrLow 20
DiploidrTrayrHigh 10
DiploidrTrayrLow 10
3 30
TriploidrStickrHigh 10
3 30
DiploidrStickrHigh 10
DiploidrStickrLow 10
3 30
Table 3 The effect of growing level, method and ploidy level on shell height, weight increase and mortality levels of
Sydney rock oysters S. glomerata in Merimbula Lake from June 1994–October 1996 Data are expressed as meanSE.
Growing Growing
Ploidy Shell height
Weight Mortalities
Ž .
Ž . Ž .
level method
level mm
increase g Low
Stick Triploid
59.70.7 26.80.4
15.64.7 Diploid
57.00.2 23.00.4
18.46.0 Tray
Triploid 55.61.2
22.00.4 8.51.6
Diploid 53.50.8
18.60.6 16.53.8
High Stick
Triploid 53.50.6
21.61.0 1.80.6
Diploid 54.10.7
20.40.5 2.50.5
Tray Triploid
56.00.8 23.01.1
3.30.5 Diploid
52.71.5 19.31.0
8.61.2
It is probable that fouling organisms, especially on low trays, reduced growth rates by reducing food availability. Winter mortality occurred mainly during the second winter
Ž .
and spring June–October, 1996 . Infestation of oysters with the winter mortality
Ž .
parasite, M. roughleyi was evident in the October, 1996 samples Table 2 . Shell height did not differ with ploidy when analysed using single factor ANOVA
Ž .
Ž .
F s 0.155, P 0.05 , however, shell height was significantly affected P - 0.05 by Ž
. ploidy, substrate and by growing level, with a significant interaction P - 0.05 between
Ž .
growing method and growing level Table 3 . Whole weight increase was significantly Ž
. Ž
affected P - 0.05 by ploidy and substrate, again with a significant interaction P - .
0.05 between substrate and growing level. Triploids had a significantly greater whole Ž
. weight increase than diploids F s 17.580, P - 0.001 . Mortalities were affected signif-
Ž .
icantly P - 0.05 only by growing level.
4. Discussion
