168
recirculation system and at elevated animal densities.
Fundamental aspects of the feeding biology of S. proboscideus are presented in Mertens et al. (1990) and
Brendonck (1993a, b).
Materials and methods
Origin of test animals
S. proboscideus occurs from Sudan to Namibia and
South Africa, and in Arabia. The starting material was
resting egg containing dry surface mud from a rain
pool in Al Gedid, south of Khartoum, Sudan (see Rzoska, 1961; Brendonck, 1990). Test organisms stemmed
from continuous cultures kept in the laboratory since
1986.
General culture conditions
The closed recirculation culture system of Brendonck
et at. (1990) was modified for the use of inert feeds.
Each filtration unit was filled with 10 kg preconditioned gravel instead of an activated sand bed. The
size of individual pebbles was between 10 and 20 mm.
Preconditioning of the gravel was performed in a tank
with strongly aerated tapwater (100 I). Conditioning of
these pebbles was enhanced by inoculation with filterbed bacteria and by loading the medium with ureum.
Due to frequent clogging, the cyst collector (150 J-Lm
mesh size) was removed and cysts were gathered in
a netted (150 J-Lm) device mounted at the inlet of the
filtration unit.
Fairy shrimps were cultured at an initial density of
50 indo I-I (sex ratio 1:1). Animals were retained in
netted cylinderical cages providing a culture volume
of about 6 I suspended in aerated tap water. The photoperiod was 12L:12D, and temperature was thermostatically maintained at 25± 1°C. For algae and inert
feeds at high density, three tanks were run in parallel.
Only two replicates were used for inert feeds at the
lower food density.
Food andfeeding regime
Micronized agro-industrial wastes were used as inert
feeds: YM20 (a mixture of corn and pea; available from
Artemia Systems, Baasrode, Belgium) and POME
(Palm Oil Mill Effluent imported from Malaysia;
obtained from the Artemia Reference Centre, Ghent,
Belgium). Average particle sizes of YM20 and POME
were 14.90±5.21 J-Lm (n=50) and 16.42±13.05 J-Lm
(n = 50), respectively. The dry feeds were tested in two
regimes: 0.1 and 0.2 mg DW animal- I h- I , respectively. The microalgae, Selenastrum capricornutum,
maintained at a density of 2±O.82 x 10 5 cells ml- I ,
proved adequate in preliminary screening experiments,
and served as the reference diet.
Food preparation and distribution
Each dry feed (5 or 10 g, for low and high feeding
regime, respectively) was added to 1 I of aerated tapwater, homogenized for 2 minutes and stored at 4°C.
Strong aeration kept the particles in suspension. Food
suspensions were distributed to the respective culture
tanks on a semi-continuous (hourly) basis by means of
timer-controlled peristaltic pumps. Dry food suspensions were prepared every two days.
Separate timers were used for dry and algal food.
Each hour, 30 ml of the dry food suspension was supplied during 15 minutes throughout the culture period.
The supply of algal suspension was adjusted according
to the cell concentration required in the culture tanks
(2 x 10 5 cells ml- I ).
Test animals
Freshly hatched nauplii were reared in 50 I aquaria
equipped with an Eheim{T M) filter. Larvae were fed
ad libitum a mixed diet of algae, YM20 and POME.
Juveniles were transferred to thf: experimental cultures
when they were approx. 5-6 mm long, which is the
minimum size to be retained in the netted test cages.
Animals were acclimated for three days to experimental conditions.
Observations and measurements
Selected physical, chemical and biological variables
were monitored at weekly intervals for 6 weeks. In all
tanks animal numbers were followed to assess weekly
mortality rates. Dead animals were replaced by individuals of similar age to maintain initial densities.
Growth in each unit was monitored by length measurements of ten randomly collected females, using
a Wild M-5 stereoscope equipped with camera lucida
and digitizing tablet. Per tank, a random sample of
50 females was checked for the presence of cysts in
the brood pouch, consequently, ten randomly collected ovigerous females were isolated in separate cages
fitted within the respective tanks, until cyst deposi-
recirculation system and at elevated animal densities.
Fundamental aspects of the feeding biology of S. proboscideus are presented in Mertens et al. (1990) and
Brendonck (1993a, b).
Materials and methods
Origin of test animals
S. proboscideus occurs from Sudan to Namibia and
South Africa, and in Arabia. The starting material was
resting egg containing dry surface mud from a rain
pool in Al Gedid, south of Khartoum, Sudan (see Rzoska, 1961; Brendonck, 1990). Test organisms stemmed
from continuous cultures kept in the laboratory since
1986.
General culture conditions
The closed recirculation culture system of Brendonck
et at. (1990) was modified for the use of inert feeds.
Each filtration unit was filled with 10 kg preconditioned gravel instead of an activated sand bed. The
size of individual pebbles was between 10 and 20 mm.
Preconditioning of the gravel was performed in a tank
with strongly aerated tapwater (100 I). Conditioning of
these pebbles was enhanced by inoculation with filterbed bacteria and by loading the medium with ureum.
Due to frequent clogging, the cyst collector (150 J-Lm
mesh size) was removed and cysts were gathered in
a netted (150 J-Lm) device mounted at the inlet of the
filtration unit.
Fairy shrimps were cultured at an initial density of
50 indo I-I (sex ratio 1:1). Animals were retained in
netted cylinderical cages providing a culture volume
of about 6 I suspended in aerated tap water. The photoperiod was 12L:12D, and temperature was thermostatically maintained at 25± 1°C. For algae and inert
feeds at high density, three tanks were run in parallel.
Only two replicates were used for inert feeds at the
lower food density.
Food andfeeding regime
Micronized agro-industrial wastes were used as inert
feeds: YM20 (a mixture of corn and pea; available from
Artemia Systems, Baasrode, Belgium) and POME
(Palm Oil Mill Effluent imported from Malaysia;
obtained from the Artemia Reference Centre, Ghent,
Belgium). Average particle sizes of YM20 and POME
were 14.90±5.21 J-Lm (n=50) and 16.42±13.05 J-Lm
(n = 50), respectively. The dry feeds were tested in two
regimes: 0.1 and 0.2 mg DW animal- I h- I , respectively. The microalgae, Selenastrum capricornutum,
maintained at a density of 2±O.82 x 10 5 cells ml- I ,
proved adequate in preliminary screening experiments,
and served as the reference diet.
Food preparation and distribution
Each dry feed (5 or 10 g, for low and high feeding
regime, respectively) was added to 1 I of aerated tapwater, homogenized for 2 minutes and stored at 4°C.
Strong aeration kept the particles in suspension. Food
suspensions were distributed to the respective culture
tanks on a semi-continuous (hourly) basis by means of
timer-controlled peristaltic pumps. Dry food suspensions were prepared every two days.
Separate timers were used for dry and algal food.
Each hour, 30 ml of the dry food suspension was supplied during 15 minutes throughout the culture period.
The supply of algal suspension was adjusted according
to the cell concentration required in the culture tanks
(2 x 10 5 cells ml- I ).
Test animals
Freshly hatched nauplii were reared in 50 I aquaria
equipped with an Eheim{T M) filter. Larvae were fed
ad libitum a mixed diet of algae, YM20 and POME.
Juveniles were transferred to thf: experimental cultures
when they were approx. 5-6 mm long, which is the
minimum size to be retained in the netted test cages.
Animals were acclimated for three days to experimental conditions.
Observations and measurements
Selected physical, chemical and biological variables
were monitored at weekly intervals for 6 weeks. In all
tanks animal numbers were followed to assess weekly
mortality rates. Dead animals were replaced by individuals of similar age to maintain initial densities.
Growth in each unit was monitored by length measurements of ten randomly collected females, using
a Wild M-5 stereoscope equipped with camera lucida
and digitizing tablet. Per tank, a random sample of
50 females was checked for the presence of cysts in
the brood pouch, consequently, ten randomly collected ovigerous females were isolated in separate cages
fitted within the respective tanks, until cyst deposi-