Nutrition, culturing, and more!
"Daphnia is a frequently used food source in the freshwater larviculture (i.e. for different carp species) and in the ornamental fish industry (i.e. guppies, sword tails, black mollies and plattys etc.)
Daphnia belongs to the suborder Cladocera, which are small crustaceans that are almost exclusively living in freshwater...Species of the genus Daphnia are found from the tropics to the arctic, in habitats varying in size from small ponds to large freshwater lakes. At present 50 species of Daphnia are reported worldwide, of which only six of them normally occur in tropical lowlands.
The adult size is subjected to large variations; when food is abundant, growth continues throughout life and large adults may have a carapace length twice that of newly-mature individuals.
The nutritional value of Daphnia depends strongly on the chemical composition of their food source. However, since Daphnia is a freshwater species, it is not a suitable prey organism for marine organisms, because of its low content of essential fatty acids, and in particular (n-3) HUFA. Furthermore, Daphnia contains a broad spectrum of digestive enzymes such, as proteinases, peptidases, amylases, lipases and even cellulase, that can serve as exo-enzymes in the gut of the fish larvae.
General procedure for tank culture
Daphnia is very sensitive to contaminants, including leaching components from holding facilities. When plastic or other polymer containers are used, a certain leaching period will be necessary to eliminate toxic compounds.
The optimal ionic composition of the culture medium for Daphnia is unknown, but the use of hard water, containing about 250 mg.l-1 of CO32-, is recommended. Potassium and magnesium levels should be kept under 390 mg.l-1 and 30-240 µg. l-1, respectively. Maintenance of pH between 7 to 8 appears to be important to successful Daphnia culture. To maintain the water hardness and high pH levels, lime is normally added to the tanks. The optimal culture temperature is about 25°C and the tank should be gently aerated to keep oxygen levels above 3.5 mg.l-1 (dissolved oxygen levels below 1.0 mg.l-1 are lethal to Daphnia). Ammonia levels must be kept below 0.2 mg.l-1.
Inoculation is carried out using adult Daphnia or resting eggs. The initial density is generally in the order of 20 to 100 animals per litre.
Normally, optimal algal densities for Daphnia culture are about 105 to 106 cells. ml-1 (larger species of Daphnia can support 107 to 109 cells.ml-1). There are two techniques to obtain the required algal densities: the detrital system and the autotrophic system.
Detrital system
The “stable tea” rearing system is a culture medium made up of a mixture of soil, manure and water. The manure acts as a fertilizer to promote algal blooms on which the daphnids feed. One can make use of fresh horse manure (200 g) that is mixed with sandy loam or garden soil (1 kg) in 10 l pond water to a stable stock solution; this solution diluted two to four times can then be used as culture medium. Other fertilizers commonly used are: poultry manure (4 g.l-1) or cow-dung substrates. This system has the advantage to be self-maintaining and the Daphnia are not quickly subjected to deficiencies, due to the broad spectrum of blooming algae. However, the culture parameters in a detrital system are not reliable enough to culture Daphnia under standard conditions, i.e. overfertilization may occur, resulting in anoxic conditions and consequently in high mortalities and/or ephippial production.
Autotrophic system
Autotrophic systems on the other hand use the addition of cultured algae. Green water cultures (105 to 106 cells.ml-1) obtained from fish pond effluents are frequently used but these systems show much variation in production rate mainly because of the variable composition of algal species from one effluent to another. Best control over the culture medium is obtained when using pure algal cultures. These can be monocultures of e.g. algae such as Chlorella, Chlamydomonas or Scenedesmus, or mixtures of two algal cultures. The problem with these selected media is that they are not able to sustain many Daphnia generations without the addition of extra vitamins to the Daphnia cultures.
Resting Eggs
Resting eggs are interesting material for storage, shipment and starting of new Daphnia cultures. The production of resting eggs can be initiated by exposing a part of the Daphnia culture to a combination of stressful conditions, such as low food availability, crowding of the animals, lower temperatures and short photoperiods. These conditions are generally obtained with aging populations at the end of the season. Collection of the ephippia from the wild can be carried out by taking sediment samples, rinsing them through a 200 µm sieve and isolating the ephippia under a binocular microscope. Normally, these embryos remain in dormancy and require a diapause inhibition to terminate this status, so that they can hatch when conditions are optimal. Possible diapause termination techniques are exposing the ephippia to low temperatures, darkness, oxygen and high carbon dioxide concentrations for a minimal period of several weeks (Davison, 1969).
There is still no standard hatching procedure for Daphnia. Generally the hatching process is stimulated by exposing the ephippia to higher temperatures (17-24°C), bright white light (70 W.m-2), longer photoperiods and high levels of dissolved oxygen. It is important, however, that these shocks are given while the resting eggs are still in the ephippium. After the shock the eggs may be removed from the ephippium. The hatching will then take place after 1-14 days."
All info taken from this website.
Editing and bolding courtousy of yours truly.
"Daphnia is a frequently used food source in the freshwater larviculture (i.e. for different carp species) and in the ornamental fish industry (i.e. guppies, sword tails, black mollies and plattys etc.)
Daphnia belongs to the suborder Cladocera, which are small crustaceans that are almost exclusively living in freshwater...Species of the genus Daphnia are found from the tropics to the arctic, in habitats varying in size from small ponds to large freshwater lakes. At present 50 species of Daphnia are reported worldwide, of which only six of them normally occur in tropical lowlands.
The adult size is subjected to large variations; when food is abundant, growth continues throughout life and large adults may have a carapace length twice that of newly-mature individuals.
The nutritional value of Daphnia depends strongly on the chemical composition of their food source. However, since Daphnia is a freshwater species, it is not a suitable prey organism for marine organisms, because of its low content of essential fatty acids, and in particular (n-3) HUFA. Furthermore, Daphnia contains a broad spectrum of digestive enzymes such, as proteinases, peptidases, amylases, lipases and even cellulase, that can serve as exo-enzymes in the gut of the fish larvae.
General procedure for tank culture
Daphnia is very sensitive to contaminants, including leaching components from holding facilities. When plastic or other polymer containers are used, a certain leaching period will be necessary to eliminate toxic compounds.
The optimal ionic composition of the culture medium for Daphnia is unknown, but the use of hard water, containing about 250 mg.l-1 of CO32-, is recommended. Potassium and magnesium levels should be kept under 390 mg.l-1 and 30-240 µg. l-1, respectively. Maintenance of pH between 7 to 8 appears to be important to successful Daphnia culture. To maintain the water hardness and high pH levels, lime is normally added to the tanks. The optimal culture temperature is about 25°C and the tank should be gently aerated to keep oxygen levels above 3.5 mg.l-1 (dissolved oxygen levels below 1.0 mg.l-1 are lethal to Daphnia). Ammonia levels must be kept below 0.2 mg.l-1.
Inoculation is carried out using adult Daphnia or resting eggs. The initial density is generally in the order of 20 to 100 animals per litre.
Normally, optimal algal densities for Daphnia culture are about 105 to 106 cells. ml-1 (larger species of Daphnia can support 107 to 109 cells.ml-1). There are two techniques to obtain the required algal densities: the detrital system and the autotrophic system.
Detrital system
The “stable tea” rearing system is a culture medium made up of a mixture of soil, manure and water. The manure acts as a fertilizer to promote algal blooms on which the daphnids feed. One can make use of fresh horse manure (200 g) that is mixed with sandy loam or garden soil (1 kg) in 10 l pond water to a stable stock solution; this solution diluted two to four times can then be used as culture medium. Other fertilizers commonly used are: poultry manure (4 g.l-1) or cow-dung substrates. This system has the advantage to be self-maintaining and the Daphnia are not quickly subjected to deficiencies, due to the broad spectrum of blooming algae. However, the culture parameters in a detrital system are not reliable enough to culture Daphnia under standard conditions, i.e. overfertilization may occur, resulting in anoxic conditions and consequently in high mortalities and/or ephippial production.
Autotrophic system
Autotrophic systems on the other hand use the addition of cultured algae. Green water cultures (105 to 106 cells.ml-1) obtained from fish pond effluents are frequently used but these systems show much variation in production rate mainly because of the variable composition of algal species from one effluent to another. Best control over the culture medium is obtained when using pure algal cultures. These can be monocultures of e.g. algae such as Chlorella, Chlamydomonas or Scenedesmus, or mixtures of two algal cultures. The problem with these selected media is that they are not able to sustain many Daphnia generations without the addition of extra vitamins to the Daphnia cultures.
Resting Eggs
Resting eggs are interesting material for storage, shipment and starting of new Daphnia cultures. The production of resting eggs can be initiated by exposing a part of the Daphnia culture to a combination of stressful conditions, such as low food availability, crowding of the animals, lower temperatures and short photoperiods. These conditions are generally obtained with aging populations at the end of the season. Collection of the ephippia from the wild can be carried out by taking sediment samples, rinsing them through a 200 µm sieve and isolating the ephippia under a binocular microscope. Normally, these embryos remain in dormancy and require a diapause inhibition to terminate this status, so that they can hatch when conditions are optimal. Possible diapause termination techniques are exposing the ephippia to low temperatures, darkness, oxygen and high carbon dioxide concentrations for a minimal period of several weeks (Davison, 1969).
There is still no standard hatching procedure for Daphnia. Generally the hatching process is stimulated by exposing the ephippia to higher temperatures (17-24°C), bright white light (70 W.m-2), longer photoperiods and high levels of dissolved oxygen. It is important, however, that these shocks are given while the resting eggs are still in the ephippium. After the shock the eggs may be removed from the ephippium. The hatching will then take place after 1-14 days."
All info taken from this website.
Editing and bolding courtousy of yours truly.
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