172
Growth was also significantly better when animals
were fed high densities of YM20 (Fig. 2b). After 6
weeks, animals measured about 2 cm while they measured only 1.4-1.7 cm under all other treatments and in
Brendonck et at. (1990). Mortality steadily increased
with time and was highest in the low-food treatments.
In high food conditions and in the control, weekly mortality varied between about 5% in the first week and
15% after six weeks. Increased mortality with time
may be due to natural causes associated with aging of
the population, gradual deterioration of water quality
(especially the accumulation of nitrites), or nutritional
deficiency of the feeds.
In general, the success of inert feed applications depends on nutritional value, particle size and
digestability of the food (Lavens et at., 1987) and
nutritional requirements of the organisms being cultured (Doulliet, 1987). The mean particle sizes of
YM20 (14.9±5.2 Mm) and POME (16.4±13.1 Mm)
are very close to the mean diameter of glass spheres
(16.4±8.0 Mm) ingested by different size classes of
S. proboscideus (see Brendonck, 1993a). Information
on nutritional requirements of freshwater anostracans,
however, is lacking. The level of polyunsaturated fatty acids (PUFA) seems to be an important criterion in the selection of any food (Munuswamy et al.,
1992). Crustaceans indeed rely on their diet to obtain
polyenoic acids, essential for vitellogenesis (Clarke &
Wickins, 1980). A study on the nutritional value of
feeds and their phenotypic influence on the fatty acid
composition of S. proboscideus cysts and adults is in
progress.
D' Agostino (1980) and Douilliet (1987) indicated
that the success of Artemia cultures fed agricultural byproducts depends on the establishment of a microflora
in the cultures. It is therefore not clear if the successful
culturing of S. proboscideus on YM20 and POME may
be related to their nutritional quality or to the colonization of adventitious microorganisms, enhanced by the
chemical composition of these diets. This microflora
may either increase the digestability of the feeds or act
as a supplement.
The culture system of Brendonck et al. (1990), initially developed for the use of algae, was slightly modified for the present application with inert feeds. The
replacement of sand by a filterbed of gravel offered several advantages such as easy conditioning and renewal of pebbles, lack of anoxic layers, and low retention of food particles. Preconditioning of gravel was
enhanced by the addition of urea (CH4-N20) under
oxygen-saturated conditions, and an inoculum of nitrifying bacteria. The injection of protein metabolites to
accelerate nitrification start-up of biological filters is
a common procedure in aquaculture (see Poquillon &
Petit, 1989).
Water quality was better with dry feeds than when
algae were used (Table 4 & Brendonck et at., 1990).
Especially nitrites accumulated at higher concentrations (0.07±0.5 mg 1-1) in algae fed cultures. This is
mainly because of the use of unwashed living algae,
giving an additional nutrient load in the recirculation
system.
Our results are promising for the large-scale culturing of S. proboscideus in a cost-effective way using
several kinds of organic waste products. So the diets
applied in this study (YM20 and POME) may be considered as test-cases, showing the suitability of different types of organic waste products to obtain cheap
fairy shrimp biomass and cysts.
Future dietary screenings may be designed to
fit specific integrated culture programmes. Organic
wastes of local agro-industrial activities may be converted to fairy shrimp biomass which in turn may serve
as live food for freshwater aquaculture organisms. The
use of nutritionally suitable, inexpensive feeds instead
of algae in culturing fairy shrimps for aquatic toxicology (Centeno et at., 1993c) may furthermore considerably decrease the cost of toxicity testing.
Acknowledgments
We thank Prof. Dr G. Persoone for providing facilities to perform the present study. We also thank Prof.
Dr H. 1. Dumont, Dr N. Munuswamy, Dr L. De Meester
& Dr S. S. S. Sarma for valuable comments during
preparation of the manuscript. Mr Pauwel Bogaert
(Artemia Reference Centre) is acknowledged for the
supply of inert feeds. L. B is post-doctoral researcher
with the National Fund for Scientific Research, Belgium (N.F.WO.).
References
Brendonck, L., 1990. Redescription of the fairy shrimp Streptocephalus proboscideus (Frauenfeld, 1893) (Crustacea: Anostraca). Bull. k. belg. Inst. Nat. Wet., BioI. 59: 49-57.
Brendonck, L., 1991. Contributions to the study of the reproductive
biology of Streptocephalus proboscideus (Anostraca, StreptocephaJidae). Crustaceana 60: 145-162.
Growth was also significantly better when animals
were fed high densities of YM20 (Fig. 2b). After 6
weeks, animals measured about 2 cm while they measured only 1.4-1.7 cm under all other treatments and in
Brendonck et at. (1990). Mortality steadily increased
with time and was highest in the low-food treatments.
In high food conditions and in the control, weekly mortality varied between about 5% in the first week and
15% after six weeks. Increased mortality with time
may be due to natural causes associated with aging of
the population, gradual deterioration of water quality
(especially the accumulation of nitrites), or nutritional
deficiency of the feeds.
In general, the success of inert feed applications depends on nutritional value, particle size and
digestability of the food (Lavens et at., 1987) and
nutritional requirements of the organisms being cultured (Doulliet, 1987). The mean particle sizes of
YM20 (14.9±5.2 Mm) and POME (16.4±13.1 Mm)
are very close to the mean diameter of glass spheres
(16.4±8.0 Mm) ingested by different size classes of
S. proboscideus (see Brendonck, 1993a). Information
on nutritional requirements of freshwater anostracans,
however, is lacking. The level of polyunsaturated fatty acids (PUFA) seems to be an important criterion in the selection of any food (Munuswamy et al.,
1992). Crustaceans indeed rely on their diet to obtain
polyenoic acids, essential for vitellogenesis (Clarke &
Wickins, 1980). A study on the nutritional value of
feeds and their phenotypic influence on the fatty acid
composition of S. proboscideus cysts and adults is in
progress.
D' Agostino (1980) and Douilliet (1987) indicated
that the success of Artemia cultures fed agricultural byproducts depends on the establishment of a microflora
in the cultures. It is therefore not clear if the successful
culturing of S. proboscideus on YM20 and POME may
be related to their nutritional quality or to the colonization of adventitious microorganisms, enhanced by the
chemical composition of these diets. This microflora
may either increase the digestability of the feeds or act
as a supplement.
The culture system of Brendonck et al. (1990), initially developed for the use of algae, was slightly modified for the present application with inert feeds. The
replacement of sand by a filterbed of gravel offered several advantages such as easy conditioning and renewal of pebbles, lack of anoxic layers, and low retention of food particles. Preconditioning of gravel was
enhanced by the addition of urea (CH4-N20) under
oxygen-saturated conditions, and an inoculum of nitrifying bacteria. The injection of protein metabolites to
accelerate nitrification start-up of biological filters is
a common procedure in aquaculture (see Poquillon &
Petit, 1989).
Water quality was better with dry feeds than when
algae were used (Table 4 & Brendonck et at., 1990).
Especially nitrites accumulated at higher concentrations (0.07±0.5 mg 1-1) in algae fed cultures. This is
mainly because of the use of unwashed living algae,
giving an additional nutrient load in the recirculation
system.
Our results are promising for the large-scale culturing of S. proboscideus in a cost-effective way using
several kinds of organic waste products. So the diets
applied in this study (YM20 and POME) may be considered as test-cases, showing the suitability of different types of organic waste products to obtain cheap
fairy shrimp biomass and cysts.
Future dietary screenings may be designed to
fit specific integrated culture programmes. Organic
wastes of local agro-industrial activities may be converted to fairy shrimp biomass which in turn may serve
as live food for freshwater aquaculture organisms. The
use of nutritionally suitable, inexpensive feeds instead
of algae in culturing fairy shrimps for aquatic toxicology (Centeno et at., 1993c) may furthermore considerably decrease the cost of toxicity testing.
Acknowledgments
We thank Prof. Dr G. Persoone for providing facilities to perform the present study. We also thank Prof.
Dr H. 1. Dumont, Dr N. Munuswamy, Dr L. De Meester
& Dr S. S. S. Sarma for valuable comments during
preparation of the manuscript. Mr Pauwel Bogaert
(Artemia Reference Centre) is acknowledged for the
supply of inert feeds. L. B is post-doctoral researcher
with the National Fund for Scientific Research, Belgium (N.F.WO.).
References
Brendonck, L., 1990. Redescription of the fairy shrimp Streptocephalus proboscideus (Frauenfeld, 1893) (Crustacea: Anostraca). Bull. k. belg. Inst. Nat. Wet., BioI. 59: 49-57.
Brendonck, L., 1991. Contributions to the study of the reproductive
biology of Streptocephalus proboscideus (Anostraca, StreptocephaJidae). Crustaceana 60: 145-162.