2. Materials and methods
The Avondale Research Station is located in the Western Australian wheatbelt near Ž
X X
. Beverley 32
87 S, 116855 E . There were 25 clay ponds at the research station. Each pond was 1.5 m deep with a 10 = 10 m water surface area, 3:1 batter and a level floor.
Ponds were individually fenced to prevent movement of yabbies between treatments. All 25 ponds received water from the same supply dam. The ponds were filled prior to
stocking and thereafter topped up to replace water lost due to evaporation.
Eighteen of these 0.01-ha ponds were stocked with yabbies obtained from local harvestors at an initial density of 1rm
2
. Prior to stocking, the 1800 yabbies in this experiment were sexed by manual examination for the presence of penes at the base of
the fifth pair of periopods for males, or gonopores at the base of the third pair of periopods for females. Intersex animals were excluded from the study.
A completely randomized block design with two factors, sex and diet, was used. Ž
. Factor sex had three levels, male, female and mixed-sex 1:1 ratio . Factor diet also had
Ž .
y2 y1
Ž .
y2
three levels, Lupin Lupinus albus 2.5 g m week
, Lupin L. albus 5.0 g m
y1
Ž .
y2 y1
Ž week
and WA Crayfish Reference Diet CRD 2.5 g m week
Morrissy, 1990, .
1992; Lawrence et al., 1998 . There were two blocks: the first block consisted of northern ponds and the second block consisted of southern ponds.
A random sample of yabbies was weighed prior to stocking each treatment. The mean Ž
. Ž
. stocking weight S.E. of yabbies in this experiment was 19.2 0.3 g
n s 180 . Ž
. There was no significant difference P s 0.08 in the average initial weight for male
Ž . Ž
. Ž
. Ž .
19.3 0.2 g n s 90 and female 19.1 0.4 g
n s 90 yabbies by a two-tailed t-test.
The ponds were stocked in July 1995 and harvested after 175 days so as to include five months of the yabby breeding season. All yabbies were removed by first trapping
then draining the ponds to collect the remaining animals. Immediately after harvesting all yabbies were individually sexed and weighed.
Gross valuerha was calculated according to current industry values for standard size Ž
categories assuming that juveniles less than 30 g have no commercial value Lawrence, .
1998 .
3. Results
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