Common flea cancer

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Common flea cancer
Cluster of common amphipods (Gammarus pulex)

Cluster of common amphipods ( Gammarus pulex )

Superordinate : Satchel Shrimp (Peracarida)
Order : Flea crabs (Amphipoda)
Subordination : Gammaridea
Family : Gammaridae
Genre : Gammarus
Type : Common flea cancer
Scientific name
Gammarus pulex
( Linnaeus , 1758)

The Common freshwater shrimp ( Gammarus pulex ) is in Europe and Central Asia beheimateter freshwater cancer, which the amphipods (amphipods), an order of crustaceans heard. Of Linnaeus it was originally Cancer pulex called. It is a type of the genus Gammarus . Rivulogammarus pulex is a now invalid junior synonym for common flea cancer . Previously, he was often referred to as freshwater shrimp called, now that name is occurring mostly only for also in streams, very similar amphipod Gammarus fossarum used.

Origin of name

The generic name is derived from the Latin gammarus (also: cammarus), related to the Greek (κάμμαρος, kammaros), which means "sea crab" or "lobster" (in the Romance languages ​​the word has survived somewhat modified to this day as the name of the lobster) . The species name pulex means flea in Latin.


The adult males of the common amphipods reach a length of 2.1 cm, the females are no more than 1.4 cm long. The color ranges from whitish-yellow to ocher and gray to greenish.

The body of common amphipods is flattened on the sides, typical of amphipods. In the rest position, the body is curved in an almost semicircular shape on the abdomen. They move crawling on their side, but when swimming in a normal position with their backs up. The body is divided into three parts: The head-chest piece is a fusion of the head with the first thoracic segment . Its extremities, which functionally serve as mouth limbs , are called maxillipedas . The second part of the body is called the peraeon and consists of seven more thoracic segments on which the seven pairs of breast bones ( peraeopods ) sit. The hips ( coxes ) of the first four pairs of legs are widened to form distinct, flattened coxal plates, through which the peraeon appears widened and divided into two parts when viewed from the side. The abdomen consists of six segments and is called the pleon . The legs sitting on the front section, the pleosome, are called swimming legs ( pleopods ). The segments are drawn down laterally to form plate-like widenings, which are called epimers. The back part of the pleon is called the urosome. At its segments set three pairs as uropods designated gap legs on. The conclusion is a pointed telson .

The head carries two pairs of antennae . The first antennae are about half the length of the body, they consist of a three-segmented stalk (pedunculus) and a 23-membered, evenly curled flagellum, in addition to the pedunculus sits a five-membered short minor whip. The second antennae (antennae) are noticeably shorter than the first. They consist of two base members and an extended end part, which corresponds to the endopodite of the cancerous split bone . It consists of three elongated limbs and a 16-limbed flagellum. The flagellum limbs are noticeably widened in the male and have long two rows of bristles on the underside, giving them a brush-like appearance (species characteristic). A kidney-shaped complex eye sits behind the antennae pairs . The mouthparts consist of mandibles and two pairs of maxillae . The mandibles consist of an enlarged base member (coxa), which forms a forceps-shaped bite tool (molar), and a feeler (palpus) formed from the endopod. The pairs of maxillae consist of two plate-shaped appendages each with long rows of bristles and a palpus . The oral cavity is closed at the back by the maxillipedas, which work as a unit through the coalescence of the coxae.

The two front peraeopods (gnathopods) serve as scissor-shaped grasping tools. The scissors consist of a massive base member (propodus) and a small, finger-shaped end member (dactylus), which is folded like a pocket knife against the base member ("subchelate" scissors). The five rear pairs are designed as striding legs. At the base of the second to sixth Peraeopod sit five pairs of plate-shaped gills (Branchiae), which serve to take up the oxygen from the water. Due to the incessant beating of the pleopods, the gills are additionally supplied with fresh breath water. There is a strong claw at the end of each leg. If the animal gives up its semicircular resting position and stretches, the pleopods' beating causes a backward flow of water. In addition to their normal function, they are also used as swimming legs. The third and fourth pairs of peraeopods support the swimming movement. In the female, there are five pairs of long appendages on the inside of the same pairs of legs that carry the gills, which are called oostegites. They delimit a partially open brood space (marsupium) on the stomach side between the leg bases.

The uropods, like most of the original crab legs ( split legs ), consist of two branches. In Gammarus pulex the inner branch of the third uropod is more than half as long as the outer branch. In this feature it differs from Gammarus fossarum , whose inner branch on the third uropod does not reach half the length of the outer branch. Gammarus pulex differs from sea flea shrimp ( Gammarus lacustris ) by the bristling on the flagellum of the second antennae of the males. This flagellum is thickened, on the inside there are two rows of eight to ten tight, half-long bristles that give the trimmings a brush-like appearance. This bristling is only moderately developed in the sea flea shrimp. This can also be recognized by the very pointed rear corners of the second epimer.


Gammarus pulex is widespread in most of Europe and northern Asia, south to Turkey, east to China. It is absent in parts of south-western Europe, for example in Spain (replaced here by Echinogammarus berilloni ) and in Italy south of the Alps, here replaced by the recently separated Gammarus italicus . The species was introduced to Ireland by humans and displaces endemic freshwater populations of the related species Gammarus duebeni . It is rarely found in underground waters ( stygobiont ); corresponding populations were described as a separate subspecies Gammarus pulex cognominis Karaman & Pinkster 1977.

Its main distribution is in streams of the lowlands. Above about 400 to 450 m above sea level. In Germany it is mostly replaced by its sister species Gammarus fossarum . It is therefore rare in the Alpine countries. So he is missing z. B. in Vorarlberg completely. In southern parts of its range, e.g. B. Already in the French Massif Central, but it can sometimes penetrate up to over 1000 meters above sea level. In the lowlands, contrary to previous assumptions, both species often occur next to each other, often as mixed populations in the same body of water. Gammarus pulex occurs in the lowlands up to the headwaters.

Competition with other species of flea

Gammarus pulex is a Eurocean species that can live in most flowing and standing waters. Within its range, its actual occurrence is limited by competition with other species of amphipods. In addition to the relatively few native species, numerous exotic species (neozoa) that have been introduced in recent years have displaced the species from some of the previously populated waters.

Competition with Gammarus fossarum

Gammarus pulex is superior to Gammarus fossarum in waters with lower currents; both occur together, preferably microhabitats with slower flow through pulex . It is also less sensitive to oxygen deficits; this is reflected in its index value in the saprobic system (2.0, compared to 1.5 for fossarum ). It also prefers warmer waters. In the absence of fossarum , it can successfully colonize most of the types of water that it colonizes.

Competition with Gammarus tigrinus

The North American Gammarus tigrinus was founded in Central Europe in 1957 by Dr. Wolfgang Schmitz intentionally settled in Werra and Weser as a replacement after pulex had died out there due to salt pollution (from wastewater from the potash industry). He prefers brackish water habitats. In the meantime, however, oligohaline populations have emerged in numerous places in Europe, which can displace Gammarus pulex in some waters with a low salt content or even in pure fresh water , e.g. B. in the Netherlands or in Brittany. Gammarus tigrinus only predominates in warm, mostly organically polluted waters. Displacement has not yet been observed in Germany, even if populations of tigrinus have been found in pure fresh water.

Competition with Dikerogammarus villosus

In parts of its distribution area, Gammarus pulex is now being displaced by the introduced neozoic flea shrimp species Dikerogammarus villosus . This can displace the native species not only through competition, but also directly through predatory feeding from its preferred waters, these are mainly shipping canals and large rivers. In brooks, the preferred habitat of Gammarus pulex , Dikerogammarus villosus does not seem to penetrate.


The common flea shrimp lives in fresh water . It occurs in stagnant waters, but clearly prefers flowing waters , so it is flow-loving (rheophilous). Within the rivers it prefers the middle and lower reaches of streams ( meta- and hyporhithral ). It still occurs subordinately in upper reaches of the river ( Epipotamal ), but no longer in middle or lower reaches. It is widespread and very common in the streams. In investigations into Hessian rivers within the framework of the Water Framework Directive , Gammarus pulex z. B. found in 597 of 1025 examined water sections; it was the second most common type of macrozoobenthos (after the mayfly Baetis rhodani ). In optimal waters, the species can reach population densities of up to 10,000 individuals per square meter, but densities of a few hundred are more typical.

Gammarus pulex is very sensitive to anthropogenic water acidification. Even moderately acidic waters with pH values ​​of 6.0 lead to a considerable increase in mortality and reduced growth rates. The effect was somewhat mitigated by high levels of humic substances , but not eliminated. The species is therefore more common in calcareous waters, it is absent in naturally acidic waters such as z. B. Bog waters.


Fall foliage from deciduous trees that has fallen into the water is the main food source of the species. The animals can bite open the leaf blades of the dead leaves and so break up the tissue. This type of diet is called "shredder" in limnology. Gammarids like the common flea shrimp are mostly the dominant and ecologically most important shredder species in Central European rivers. From food choice experiments and field observations it is known that the deciduous species for Gammarus pulex are not of the same food quality. Stiff, firm leaves with a high tannin or lignin content are less likely to be eaten. Preferred deciduous species are alder, poplar and willow, beech leaves are less popular, and oak leaves and needles from conifer species are least suitable as food. Partially decomposed leaves with high biomass of fungi are clearly preferred. Neither bacteria nor fungal spores are digested to any significant extent. The animals prefer flushed packs of leaves in streams as a lounge. In late summer, before the new leaves fall, they can use up the leaf biomass to such an extent that the population growth is limited by a lack of food.

Although the role of the gammarids as shredders is strongly emphasized in limnological research, Gammarus pulex is in reality omnivorous . The animals can graze on algae and organic coatings (the biofilm ) from stones and also bite higher aquatic plants (macrophytes). They are also predators when opportunities arise, ie when prey animals are not too fast and not too hard-armored, e.g. B. Mayfly or mosquito larvae. Also carrion like z. B. dead fish is gladly accepted. They are essentially opportunists here who take advantage of every possible source of food. However, they also prey on mayfly larvae if they have enough high-quality leaf food available.

A popular food source of the species are other amphipods, both related and of its own species. It is therefore partially cannibalistic. In addition to small young animals, only freshly skinned, not yet hardened animals can be overpowered. Be equally adopted isopods , the Gammarus pulex can thus from his preferred waters displace.

Life cycle

The gender identification of Gammarus pulex is based on pheromones that are released by the female and perceived by the male with his antennae. The molting hormone ecdysone may have a pheromone function. Female Gammarus pulex individuals can only be fertilized and lay eggs immediately after moulting. In order to ensure fertilization, the larger males cling to the female's back with their scissor-like first gnathopods and wait for it to moult. Occasionally there are mismatches with fossarum . The second gnathopods are meaningless for holding on, but have an important function in mating itself. The pairs stay together for a long time, up to weeks, and are almost as mobile as individual animals, although the difference in size is an advantage. Surprisingly, pairing appears not only to be based on competition between the males, but could even be beneficial for the females. For the actual copulation, the male lets go, swims to the female's belly and releases his sperm there. The fertilization takes place externally.

The female does not lay her eggs freely, but in the brood pouch (marsupium) on her belly, in which she then carries them around with her. When they are deposited, the eggs are surrounded by a gelatinous shell that gradually dissolves. The size of a clutch of eggs depends on the body size of the female, and thus also indirectly on its age (since the animals grow their entire life and older females are larger as a result). It is normally 15 to a maximum of about 30 eggs, with very small females (first brood) only 6 to 7. Three reproductive cycles with one egg clutch each are possible. This high number is not always reached. In the Turkish river Yeşilırmak there are e.g. B. essentially only one period in the spring when young are given off. Common amphipods can reach an age of two years and produce five to six broods during this time, but most animals do not live to be more than a year old.

The young hatch from the egg after about 20 to 23 days and are then about 1.6 to 1.8 mm long. The female then carries the young around with her for about two days (a little longer at low water temperatures) before releasing them into the open water. The animals become sexually mature after 11 (at 20 ° C) to 52 (at 5 ° C) weeks, depending on the water temperature. Depending on the time of year they hatch, they can reproduce for the first time in the same year or in the following year.

The breeding period of the species is quite extended. Egg-bearing females can be observed almost all year round. However, reproduction is mostly limited to the summer half-year, no eggs are laid between October (November) and March. This also applies in southern parts of the distribution area such as in Anatolia. Egg-bearing females then only appear in exceptional cases, or they hold the eggs until spring, pairs are not formed. During this time, the oostegites of the brood ashes are somewhat receded when molting and lose their long fringes.

Individuals of Gammarus pulex go through numerous moltings during their lifetime. The moulting phases follow one another in days to a few weeks, so that it is not possible to differentiate the stages on the basis of size classes. The animals continue to shed their skin throughout their life, even during sexual maturity. The cuticle, which is shed during the moult, contains calcium deposits, which means that this species has a high calcium requirement for its development.

Use as a bio-indicator

Gammarus pulex are used as biological indicators for drinking water quality. In the Kleistpark intermediate pumping station owned by Berliner Wasserbetriebe , the animals are kept in small chambers and monitored by sensors. An alarm is triggered if the behavior changes. For you to replace the used 2015 moderlieschen .

Individual evidence

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  4. ^ Erik Dahl (1977): The Amphipod Functional Model and Its Bearing upon Systematics and Phylogeny. Zoologica scripta. Vol. 6: 221-228.
  5. Distribution map at
  6. Goedmakers & Pinkster 1977th
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  9. Erwin Amann (2003): Flohkrebse (Gammaridae) in Vorarlberg. Vorarlberger Naturschau 12: 65–76.
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  11. cf. z. B. Wolfgang Janetzky (1994): Distribution of the genus Gammarus (Amphipoda: Gammaridae) in the River Hunte and its tributaries (Lower Saxony, northern Germany) Hydrobiologia 294: 23-34. doi: 10.1007 / BF00017622 .
  12. Annemarie Goedmakers (1972): Gammrus fossarum Koch, 1835: redescription based on neotype material and notes on its local variation (Crustacea, Amphipoda). Bijdragen tot de Dierkunde 42 (2): 124-138.
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  14. Sjouk Pinkster, Jan Dielemann, Dirk Platvoet (1980): The present position of Gammarus tigrinus Sexton, 1939, in The Netherlands, with the description of a newly discovered amphipod species, Crangonyx pseudogracilis Bousfield, 1958 (Crustacea, Amphipoda). Bulletin Zoological Museum Universiteit van Amsterdam vol. 7 no. 4: 33-45.
  15. Christophe Piscart, Chafik Maazouzi, Pierre Marmonier (2008): Range expansion of the North American alien amphipod Gammarus tigrinus Sexton, 1939 (Crustacea: Gammaridae) in Brittany, France. Aquatic Invasions (2008) Volume 3, Issue 4: 449–453, doi: 10.3391 / ai.2008.3.4.15 .
  16. Michael E. Zettler (1998): On the distribution of the Malacostraca (Crustacea) in the inland and coastal waters of Mecklenburg-Western Pomerania. Lauterbornia 32: 49-65.
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  18. a b Ursula Schmedtje & Manfred Colling (1996): Ecological typing of the aquatic macrofauna. Information reports from the Bavarian State Office for Water Management, issue 4/96. 548 pp.
  19. a b Hasko Nesemann, Otto Moog, Manfred Pöckl (2002): Crustacea: Amphipoda, Isopoda, Decapoda. in O. Moog (ed.): Fauna Aquatica Austriaca. Delivery III.
  20. Hessisches Landesamt für Umwelt und Geologie (Hrsg.) (2007): The macrozoobenthos in Hessian rivers - results from the early monitoring for the implementation of the European Water Framework Directive.
  21. ^ JS Welton (1979): Life-history and production of the amphipod Gammarus pulex in a Dorset chalk stream. Freshwater Biology 9: 263-275, doi: 10.1111 / j.1365-2427.1979.tb01508.x .
  22. ^ Effects of low pH and humus on the survivorship, growth and feeding of Gammarus pulex (L.) (Amphipoda) . In: Freshwater Biology . tape 19 , no. 2 , April 1, 1988, pp. 235-247 , doi : 10.1111 / j.1365-2427.1988.tb00345.x .
  23. ^ John HR Gee (1982): Resource utilization by Gammarus pulex (Amhipoda) in a Cotswold stream: a microdistribution study. Journal of Animal Ecology Volume 51, Issue 3: 817-831.
  24. ^ C. MacNeil, JTA Dick, RW Elwood (1997): The trophic ecology of freshwater Gammarus spp. (Crustacea: Amphipoda): Problems and perspectives concerning the functional feeding group concept. Biological Reviews 72: 349 - 364. doi: 10.1111 / j.1469-185X.1997.tb00017.x .
  25. David W. Kelly, Jaimie TA Dick, W. Ian Montgomery (2002): The functional role of Gammarus (Crustacea, Amphipoda): shredders, predators, or both? Hydrobiologia 485: 199-203.
  26. a b c D. W. Sutcliffe (1992): Reproduction in Gammarus (Crustacea, Amphipoda): basic processes. Freshwater Forum, 2 (2): 102-128.
  27. Kevin D. Hume, Robert W. Elwood, Jaimie TA Dick, Jenny Morrison (2005): Sexual dimorphism in amphipods: the role of male posterior gnathopods revealed in Gammarus pulex. Behavioral Ecology and Sociobiology 58: 264-269 , doi: 10.1007 / s00265-005-0925-7 .
  28. Jonathan Adams & Paul J. Greenwood (1983): Why are males bigger than females in pre-copula pairs of Gammarus pulex? Behavioral Ecology and Sociobiology 13: 239-241, doi: 10.1007 / BF00299670 .
  29. Matthias Galipaud, François-Xavier Dechaume-Moncharmont, Abderrahim Oughadou, Loïc Bollache: Does foreplay matter? Gammarus pulex females may benefit from long-lasting precopulatory mate guarding. In: Biology letters. Volume 7, number 3, June 2011, pp. 333-335, doi: 10.1098 / rsbl.2010.0924 , PMID 21068026 , PMC 3097851 (free full text).
  30. ^ HBN Hynes (1955): The Reproductive Cycle of Some British Freshwater Gammaridae. Journal of Animal Ecology Vol. 24, No. 2: 352-387.
  31. ^ A b David W. Sutcliffe (1993): Reproduction in Gammarus (Crustacea, Amphipoda): female strategies. Freshwater Forum, 3 (1): 26-64.
  32. ^ A b Mustafa Duran (2007): Life Cycle of Gammarus pulex (L.) in the River Yesilirmak. Turkish Journal of Zoology 31: 389-394.
  33. ^ DW Sutcliffe, TR Carrick, LG Willoughby (1981): Effects of diet, body size, age and temperature on growth rates in the amphipod Gammarus pulex. Freshwater Biology 11: 183-214.doi : 10.1111 / j.1365-2427.1981.tb01252.x
  34. Rainer W. During: River shrimp take care of Berlin's drinking water . In: Der Tagesspiegel Online . May 3, 2015, ISSN  1865-2263 ( [accessed March 25, 2018]).


  • David M. Holdich & Manfred Pöckl: Invasive crustaceans in European inland waters. In: Francesca Gherardi (Ed.): Biological Invaders in Inland Waters: Profiles, Distribution and Threats. Volume 2 of Invading Nature. Pp. 29-76, Springer, 2007 ISBN 978-1-4020-6028-1
  • Gerd Mayer, Andreas Maas, Dieter Waloszek (2012): Mouthpart Morphology of Three Sympatric Native and Nonnative Gammaridean Species: Gammarus pulex, G. fossarum, and Echinogammarus berilloni (Crustacea: Amphipoda). International Journal of Zoology Volume 2012, Article ID 493420, 23 pages doi: 10.1155 / 2012/493420

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