169
Weekly mortality (%)
1 00--------·-·----·-----····----·--------·----------------,
6, ALGAE
+ YM20-Low
o YM20-Hlgh
80
o POME-Low
X POME-High
60
40
20
0
0
! !
o '--__ - - - - " _ - - - . L - - - - L - - -
o
1
2
3
0
-I!i
--L
4
0
+
~
5
o
+
~
6
7
Time (weeks)
Fig. 1. Weekly mortality (%) of S. proboscideus fed YM20 and POME at low (0.1 mg DW animal-I h- I ) and high (0.2 mg DW animal-I
h- I ) food densities in comparison with microalgae, (Selenastrum capricornutum) at a density of 2±0.82 x 10 5 cells ml- I . Values represent
~=cl~~_~~~~~_~~~~~
tion (maximum 2 days). Cysts were then counted to
assess average brood size. From the average brood
size and percentage of ovigerous females present at
every observation, and taking into account the average
storage time of cysts in the brood pouch (1-2 days)
(Brendonck, 1991), the daily sustainable yield of cysts
was estimated.
Nitrogen compounds NH3-N, NOz-N, and N03-N,
and pH were monitored weekly, whereas P04 concentrations were measured every two weeks. All testing
employed a Hach DRl3 Spectrophotometer and Hach
methods.
Statistical analysis
Repeated-measures analysis was applied to compare
the weekly mean fecundity and growth values in relation to different food quantity and quality as a function of time (Wilkinson, 1990). Mean brood sizes and
lengths of animals in relation to food types and densities were analysed using One-way ANOVA with Tukey
pairwise comparisons (Sokal & Rholf, 1981).
Results
Mortality
The average weekly mortality slightly increased with
time and reached 15-30% at week 6. The population
fed a low density of POME showed slightly increased
mortality rate in comparison with the other treatments
(Fig. 1).
Growth
An overall significant influence of food type on growth
was revealed (p<0.0 1) (Fig. 2a, b & Table 3a). Animals
fed a high density of YM20 showed significantly better
growth (p
Fecundity
Cyst production was significantly higher under high
food than under low food density treatments (p<0.00 1)
(Table 1 & 3a).
Weekly mortality (%)
1 00--------·-·----·-----····----·--------·----------------,
6, ALGAE
+ YM20-Low
o YM20-Hlgh
80
o POME-Low
X POME-High
60
40
20
0
0
! !
o '--__ - - - - " _ - - - . L - - - - L - - -
o
1
2
3
0
-I!i
--L
4
0
+
~
5
o
+
~
6
7
Time (weeks)
Fig. 1. Weekly mortality (%) of S. proboscideus fed YM20 and POME at low (0.1 mg DW animal-I h- I ) and high (0.2 mg DW animal-I
h- I ) food densities in comparison with microalgae, (Selenastrum capricornutum) at a density of 2±0.82 x 10 5 cells ml- I . Values represent
~=cl~~_~~~~~_~~~~~
tion (maximum 2 days). Cysts were then counted to
assess average brood size. From the average brood
size and percentage of ovigerous females present at
every observation, and taking into account the average
storage time of cysts in the brood pouch (1-2 days)
(Brendonck, 1991), the daily sustainable yield of cysts
was estimated.
Nitrogen compounds NH3-N, NOz-N, and N03-N,
and pH were monitored weekly, whereas P04 concentrations were measured every two weeks. All testing
employed a Hach DRl3 Spectrophotometer and Hach
methods.
Statistical analysis
Repeated-measures analysis was applied to compare
the weekly mean fecundity and growth values in relation to different food quantity and quality as a function of time (Wilkinson, 1990). Mean brood sizes and
lengths of animals in relation to food types and densities were analysed using One-way ANOVA with Tukey
pairwise comparisons (Sokal & Rholf, 1981).
Results
Mortality
The average weekly mortality slightly increased with
time and reached 15-30% at week 6. The population
fed a low density of POME showed slightly increased
mortality rate in comparison with the other treatments
(Fig. 1).
Growth
An overall significant influence of food type on growth
was revealed (p<0.0 1) (Fig. 2a, b & Table 3a). Animals
fed a high density of YM20 showed significantly better
growth (p
Fecundity
Cyst production was significantly higher under high
food than under low food density treatments (p<0.00 1)
(Table 1 & 3a).