Daphnia, a genus of small planktonic crustaceans, are 0.2–5
millimetres (0.01–0.20 in) in length.
Daphnia are members of
the order Cladocera, and are one of the several small aquatic
crustaceans commonly called water fleas because their saltatory
(Wiktionary) swimming style resembles the movements of fleas. Daphnia
live in various aquatic environments ranging from acidic swamps to
freshwater lakes, ponds, streams and rivers.
The two most readily available species of
Daphnia are D. pulex
(small and most common) and D. magna (large). They are often
associated with a related genus in the order Cladocera: Moina, which
is in the
Moinidae family instead of
Daphniidae and is much smaller
than D. pulex (approximately half the maximum length). Daphnia
eggs for sale are generally enclosed in ephippia (a thick shell,
consisting of two chitinous plates, that encloses and protects the
winter eggs of a cladoceran).
1 Appearance and characteristics
2 Systematics and evolution
3 Ecology and behaviour
4 Life cycle
7 Invasive species
8 See also
10 External links
Appearance and characteristics
The beating heart of
Daphnia under the microscope
The body of
Daphnia is usually 1–5 millimetres (0.04–0.20 in)
long, and is divided into segments, although this division is not
visible. The head is fused, and is generally bent down towards the
body with a visible notch separating the two. In most species, the
rest of the body is covered by a carapace, with a ventral gap in which
the five or six pairs of legs lie. The most prominent features are
the compound eyes, the second antennae, and a pair of abdominal
setae. In many species, the carapace is translucent or nearly so
and as a result they make excellent subjects for the microscope as one
can observe the beating heart.
Even under relatively low-power microscopy, the feeding mechanism can
be observed, with immature young moving in the brood pouch; moreover,
the eye being moved by the ciliary muscles can be seen, as well as
blood cells being pumped around the circulatory system by the simple
heart. The heart is at the top of the back, just behind the head,
and the average heart rate is approximately 180 bpm under normal
conditions. Daphnia, like many animals, are prone to alcohol
intoxication, and make excellent subjects for studying the effects of
the depressant on the nervous system due to the translucent
exoskeleton and the visibly altered heart rate. They are tolerant
of being observed live under a cover slip and appear to suffer no harm
when returned to open water. This experiment can also be performed
using caffeine, nicotine or adrenaline, each producing an increase in
the heart rate.
Systematics and evolution
Main article: List of
Daphnia is a large genus – comprising over 200 species – belonging
to the cladoceran family Daphniidae. It is subdivided into several
subgenera (Daphnia, Australodaphnia, Ctenodaphnia), but the division
has been controversial and is still in development. Each subgenus has
been further divided into a number of species complexes. The
understanding of species boundaries has been hindered by phenotypic
plasticity, hybridization, intercontinental introductions and poor
Ecology and behaviour
Anatomy of Daphnia
The five trunk limbs, used in filter-feeding
Daphnia species are normally r-selected, meaning that they invest in
early reproduction and so have short lifespans. An individual Daphnia
life-span depends on factors such as temperature and the abundance of
predators, but can be 13–14 months in some cold, oligotrophic
fish-free lakes. In typical conditions, however, the life cycle is
much shorter, not usually exceeding 5–6 months.
Daphnia are typically filter feeders, ingesting mainly unicellular
algae and various sorts of organic detritus including protists and
bacteria Beating of the legs produces a constant current
through the carapace which brings such material into the digestive
tract. The trapped food particles are formed into a food bolus which
then moves down the digestive tract until voided through the anus
located on the ventral surface of the terminal appendage. The
second and third pair of legs are used in the organisms' filter
feeding, ensuring large unabsorbable particles are kept out, while the
other sets of legs create the stream of water rushing into the
Swimming is powered mainly by the second set of antennae, which are
larger in size than the first set. The action of this second set
of antennae is responsible for the jumping motion.
Resting egg pouch (ephippium) and the juvenile daphnid that just has
hatched from it
Daphnia species have a life cycle based on "cyclical
parthenogenesis", alternating between parthenogenetic (asexual)
reproduction and sexual reproduction. For most of the growth
season, females reproduce asexually. They produce a brood of diploid
eggs every time they moult; these broods can contain as few as 1–2
eggs in smaller species, such as D. cucullata, but can be over
100 in larger species, such as D. magna. Under typical
conditions, these eggs hatch after a day, and remain in the female's
brood pouch for around three days (at 20 °C). They are then
released into the water, and pass through a further 4–6 instars over
5–10 days (longer in poor conditions) before reaching an age where
they are able to reproduce. The asexually produced offspring are
Towards the end of the growing season, however, the mode of
reproduction changes, and the females produce tough "resting eggs" or
"winter eggs". When environmental condition deteriorate (e.g.
crowding), some of the asexually produced offspring develop into
males. The females start producing haploid sexual eggs, which the
males fertilise. In species without males, resting eggs are also
produced asexually and are diploid. In either case, the resting eggs
are protected by a hardened coat called the ephippium, and are cast
off at the female's next moult. The ephippia can withstand periods of
extreme cold, drought or lack of food availability, and hatch – when
conditions improve – into females (They are close to being classed
as extremophiles) .
Daphnia species are considered threatened. The following are
listed as vulnerable by IUCN:
Daphnia occidentalis, and
Daphnia jollyi. Some species are halophiles,
and can be found in hypersaline lake environments, an example of which
is the Makgadikgadi Pan.
Daphnia spp. are a popular live food in tropical and marine fish
keeping. They are often fed to tadpoles or small species of
amphibians such as the
African dwarf frog
African dwarf frog (Hymenochirus boettgeri).
Daphnia may be used in certain environments to test the effects of
toxins on an ecosystem, which makes them an indicator genus,
particularly useful because of its short lifespan and reproductive
capabilities. Because they are nearly transparent, their internal
organs are easy to study in live specimens (e.g. to study the effect
of temperature on the heart rate of these ectothermic organisms).
Daphnia is also commonly used for experiments to test climate change
aspects, as ultraviolet radiation (UVR) that seriously damage
zooplankton species (e.g. decrease feeding activity).
Because of their thin membrane, which allows drugs to be absorbed,
they are used to monitor the effects of certain drugs, such as
adrenaline or capsaicin, on the heart.
Fishhook waterflea (above) and
Bythotrephes longimanus (spiny water
Some species of daphnia or water fleas that resemble daphnia have
developed permanent, non-temporary defenses against fish eating them
such as spines and long hooks on the body which also cause them to
become entangled on fishing lines and cloud water with their high
numbers. Species such as Bythotrephes longimanus AKA
"spiny water flea" and formerly known as Bythotrephes cederstroemi
(native to Northern Europe and Asia),
Cercopagis pengoi AKA "fishhook
waterflea" (native in the brackish fringes of the Black Sea and the
Caspian Sea) and
Daphnia lumholtzi (native to east
Africa, the Asian subcontinent of India, and east Australia) have
these characteristics and great care should be taken to prevent them
from spreading further in North American waters.
Some species of daphnia native to North America can develop sharp
spines at the end of the body and helmet-like structures on the head
when they detect predators, but this is overall temporary for
such daphnia species and they do not completely overwhelm or
discourage native predators from eating them. While daphnia are an
important base of the food chain in freshwater lakes (and vernal
pools), they become a nuisance when they are unable to be eaten by
native macroscopic predators and there is some concern that the
original spineless and hookless water fleas and daphnia end up
out-competed by the invasive ones. (This may not be the case, however,
and the new invaders may mostly be a tangling and clogging nuisance.)
Moina, which are sometimes referred to as Daphnia
^ a b A. Kotov; L. Forró; N. M. Korovchinsky; A. Petrusek (March 2,
Cladocera checkList" (PDF). World checklist of
Cladocera species. Belgian
Biodiversity Platform. Retrieved
October 29, 2012.
^ N.N.Smirnov (2014). The physiology of the Cladocera. Amsterdam:
^ a b c d e f g Dieter Ebert (2005). "Introduction to Daphnia
biology". Ecology, Epidemiology, and Evolution of Parasitism in
Daphnia. Bethesda, MD: National Center for Biotechnology Information.
^ a b c d e f "Daphnia". Oneida Lake Education Initiative. Stony Brook
University. Retrieved October 9, 2013.
^ a b "Investigating factors affecting the heart rate of Daphnia".
Nuffield Foundation. January 25, 2012. Retrieved October 9,
^ Niles Lehman; Michael E. Pfrender; Phillip A. Morin; Teresa J.
Crease; Michael Lynch (1995). "A hierarchical molecular phylogeny
within the genus Daphnia". Molecular Phylogenetics and Evolution. 4
(4): 395–407. doi:10.1006/mpev.1995.1037. PMID 8747296.
^ Derek J. Taylor; Paul D. N. Hebert; John K. Colbourne (1996).
"Phylogenetics and evolution of the
Daphnia longispina group
(Crustacea) based on 12S rDNA sequence and allozyme variation" (PDF).
Molecular Phylogenetics and Evolution. 5 (3): 495–510.
doi:10.1006/mpev.1996.0045. PMID 8744763. [permanent dead
^ Sarah J. Adamowicz; Paul D. N. Hebert; María Christina Marinone
(2004). "Species diversity and endemism in the
Daphnia of Argentina: a
genetic investigation". Zoological Journal of the Linnean Society. 140
(2): 171–205. doi:10.1111/j.1096-3642.2003.00089.x.
^ a b Barbara Pietrzak; Anna Bednarska; Magdalena Markowska; Maciej
Rojek; Ewa Szymanska; Miroslaw Slusarczyk (2013). "Behavioural and
physiological mechanisms behind extreme longevity in Daphnia".
Hydrobiologia. 715 (1): 125–134.
^ a b c Z. Maciej Gliwicz (2008). "Zooplankton". In Patrick
O'Sullivan; C. S. Reynolds. The Lakes Handbook: Limnology and Limnetic
Ecology. John Wiley & Sons. pp. 461–516.
^ a b Stanley L. Dodson; Carla E. Cáceres; D. Christopher Rogers
Cladocera and other Branchiopoda". In James H. Thorp; Alan P.
Covich. Ecology and Classification of North American Freshwater
Invertebrates (3rd ed.). Academic Press. pp. 773–828.
^ C. Michael Hogan (2008). "Makgadikgadi". The Megalithic
^ "The amazing
Daphnia water flea". AquaDaily. February 16, 2009.
Retrieved February 18, 2009.
^ Fernández, Carla Eloisa; Rejas, Danny (2017-04-05). "Effects of UVB
radiation on grazing of two cladocerans from high-altitude Andean
lakes". PLOS ONE. 12 (4): e0174334. doi:10.1371/journal.pone.0174334.
^ USGS Nonindigenous Aquatic Species: Bythotrephes longimanus
^ Central Michigan University:
Zooplankton of the Great Lakes:
^ Washington Department of Fish & Wildlife: Conservation:
Bythotrephes cederstroemi (Spiny waterflea)
^ USDA National Agriculture Library: Aquatic Species: Spiny Water Flea
^ USGS: Nonindigenous Aquatic Species:
^ Center for Freshwater Biology - University of New Hampshire: Daphnia
^ ISSG: Global Invasive Species Database:
^ James A. Stoeckel, Illinois Natural History Survey: Daphnia
lumholtzi: The Next Great Lakes Exotic?
^ Elizabeth A. Colburn (2004), Vernal Pools: Natural History and
Conservation, page 118 of paperback second edition from 2008
^ Patrick Lavens and Patrick Sorgeloos, Manual on the Production and
Use of Live Food for Aquaculture:
Daphnia and Moina
Wikimedia Commons has media related to Daphnia.
Data related to
Daphnia at Wikispecies
Daphnia Genomics Consortium
Daphnia Images and Information at MBL Aquaculture
Daphnia: An Aquarist's Guide
Waterflea.org: a Community resource for cladoceran biology
Daphnia spp.: taxonomy, facts, life cycle, references at GeoChemBio
Fauna Europaea: 237009