Cercopagis pengoi, (Ostroumov, 1891)

General view of the organism (with references to other INTERNET sources)

Illustrated Database at the GAAS web site http://www.zin.ru/projects/invasions/gaas/cerpen_i.htm
Photos at the Dr MacIsaac�s lab web site in Canada http://www.cs.uwindsor.ca/users/h/hughm/private/cercopagis.html
Photo at the FIMR web site
http://www2.fimr.fi/uutiset/kuvat/cercojpg.htm

Various depictions of Cercopagis (Cercopagis) pengoi (the �Cercopagis pengoi group�, from Rivier, 1998).

1 � C.(C.) neonilae (Asov Sea)
2 � C.(C.) pengoi, parthenogenetic female (Caspian Sea)
3 � C.(C.) pengoi, gamogenetic (sexual) female (Caspian Sea)
4 � C.(C.) pengoi, male (Caspian Sea)
5 - C.(C.) pengoi gracillima, parthenogenetic female (Northern Caspian)
6 - C.(C.) pengoi aralensis, parthenogenetic female (Aral Sea)

Taxonomic description of species

For correct identification of Cercopagis (Cercopagis) pengoi, the adult female is needed. Useful characters of the female include the caudal process bearing 3 pairs of spines and a loop on the end, and embryos (instar III of parthenogenetic) or resting eggs (instar III of gamogenetic, or sexual, female) in the brood pouch. Cercopagis pengoi differs from other members of subgenus Cercopagis in body proportion: abdomen length is equal to length of the rest of body, and spines are large, equal to 2-3 diameters of caudal process. Body length ranges up to 1.2-2.2 mm. Recently, it has been shown that parthenogenetic females of the first generation of C.(C.)pengoi, which hutched from resting eggs, are morphologically distinct from parthenogenetic females of following generations. They resemble �.(Apagis) ossiani M.-Bolt., which is characterized by 4 pairs of caudal spines, significantly shortened caudal process without a loop, and maximal fecundity (Simm and Ojaveer, 1999; Grigorovich et al., 2000; Rivier unpubl.)
The third instar of the gamogenetic female is larger than parthenogenetic female. Females with 2 resting eggs in the brood pouch are the largest specimens in the population. Sexual females carry developing resting eggs within the ovaries, visible as large dark spot under the base of the developed but empty brood pouch.
Males are smaller than the parthenogenetic female, with body length up to 1.2-1.8 mm. The male abdomen is shorter than rest of body, and the head and eye are comparatively larger than in the female. The male caudal process is shorter, and distances between spines on the caudal process are significantly shorter than in females. Thoracopod I in males bears a toothed hook. Males also possess paired penis behind thoracopods IV. On the dorsal side of the trunk, males bear a tubercule outgrowth (with heart within it), resembling the brood pouch of newborn females.
Parthenogenetic and gamogenetic females and males possess 3 life-history stages (instars), differ by number of spines on the caudal process. The newborn parthenogenetic females have one pair of spines on the caudal process (instar I parthenogenetic female), compact oval embryos in the brood pouch without a pointed apex. The second stage (instar II) of the parthenogenetic female has two pairs of caudal spines. The mature stage (instar III) of the parthenogenetic female has a large brood pouch with a pointed apex, and embryos disposed in a �chain� within brood pouch.
C. (C.) pengoi possesses a high degree of regional variability in morphology. Largest adult parthenogenetic females are found in the Baltic Sea, with mean body length of 1.99 mm. C. (C.) pengoi in the Caspian Sea is smaller, with mean body length of 1.73 mm, and smallest specimens are found in Lake Ontario, with mean body length of 1.45 mm. Caudal processes are largest in the instar III parthenogenetic females from the Baltic Sea (mean length 9.65 mm), medium in Lake Ontario (mean length 8.57mm), and shortest in females from the Caspian Sea (7.48mm), but relative (to body length) length of caudal process is largest in specimens in Lake Ontario (mean 5.9), medium in C.(C.) pengoi in the Baltic (4.9), and smallest in the Caspian population � 4.3 (Grigorovich et al., 2000).
Drawings of parthenogenetic instars I-III females, gamogenetic instar III females, and an instar III male from the Baltic population of C. (C.) pengoi are available at the GAAS web site (http://www.zin.ru/projects/invasions/gaas/cerpen_i.htm). Photographs of specimens from the Lake Ontario population are available at Dr. MacIsaac�s Laboratory web site (http://www.cs.uwindsor.ca/users/h/hughm/private/cercopagis.html).
Intraspecific forms. Several species of Cercopagis established by Sars (1897, 1902) are most likely intraspecific forms of a single polymorphic species C.(C.) pengoi, and are combined into the �Cercopagis pengoi group� (Rivier, 1998). This group comprises four taxa including C. pengoi (the typical form), C.neonilae, C. pengoi gracillima, and C.pengoi aralensis. Members of this group can be distinguished from all other species of the subgenus Cercopagis based on the following set of characters:
1) the presence of a pointed apex on the brood pouch;
2) proximal articular spines of the caudal process that are well-developed and extend at least ¾ the distance between the base of these spines on the caudal process and attachment point of the caudal process on the abdomen;
3) distances between adjacent pairs of articular spines that are relatively large and more or less comparable to the abdomen length in females.
Form C.(Cercopagis) neonilae Sars from the Azov Sea is distinguished by the shortened and bulged abdomen. C.(C.) pengoi aralensis M.-Bolt. from the Aral Sea area possesses an elongated abdomen, short caudal process (3-5 fold of body length) with unbended loop and shortened distances between caudal spines. Form C.(C.) pengoi gracillima is characteristic for the Northern Caspian Sea, with an extremely long abdomen, long caudal process, elongated narrow brood pouch with a large pointed apex, and an angle between abdomen and caudal process of less than 90^�. Systematic status of the C.(C.) pengoi subspecies is not clear.
Related forms. In the Caspian Sea, other members of the subgenus Cercopagis were also found: Cercopagis (Cercopagis) neonilae Sars 1902, C. (C.) socialis Grimm 1977, C.(C.) prolongata Sars 1897, C.(C.) micronyx Sars 1897, C.(C.) anonyx Sars 1897, C.(C.) robusta Sars 1897, C.(C.) longiventris Mordukhai-Boltovskoi 1964, C.(C.) spinicaudata Mordukhai-Boltovskoi 1968; members of the subgenus Apagis include: Cercopagis (Apagis) cylindrata Sars 1897, C.(A.) longispina Sars1902, C.(A.) ossiani Mordukhai-Boltovskoi 1968, C.(A.) beklemichevi Mordukhai-Boltovskoi 1964 (Rivier 1998).

Distribution of species within the Caspian Sea

First record for the Caspian Sea. Late 19th Century (Sars, 1897)
Redescription of species. Ostroumov, 1892 (Bythotrephes); Sars 1897 (tenera); Valkanov, 1951; Mordukhai-Boltovskoi, 1967, 1968; Rivier, 1969; Manuilova, 1964; Negrea, 1983; Mordukhai-Boltovskoi, Rivier 1987; Rivier, 1998; Grig�rovich et al., 2000.

General characteristics of species

Ecological-taxonomic group. Zooplankton
Origin. Caspian Sea endemic
World distribution. Caspian endemic species, which spread during different geological periods to the Ponto-Azov and Aral Sea basins; at the present time this species inhabits the Caspian, Azov, Black, Baltic seas, reservoirs of Don and Dnieper rivers, in the Great Lakes of North America .

Worldwide distribution of C.(C.) pengoi. Source: Geographic Information System �INVADER� (http://www.zin.ru/projects/invasions/gaas/invader/invader.htm)

Habitat. Cercopagis (�.) pengoi inhabits the entire water column in the shallow Northern Caspian Sea. I the Middle and Southern Caspian Sea C.(C.) pengoi is found mainly above the thermocline, while the resting eggs are stored presumably in the bottom sediments.
Migrations. Diel vertical migrations of members of the genus Cercopagis were registered in the Middle Caspian Sea (Cape Peschany, Sagandyk and Bekdash area). During the daytime, animals are distributed up to 60-160 m in depth, while during the nighttime, they are concentrated in the upper 20-40 m layer. Juveniles are more abundant in the surface layers at all the time (Rivier 1967).

Relation to abiotic environmental factors

Relation to salinity. Brackishwater euryhaline species
Cercopagis (Cercopagis) pengoi is the most euryhaline species in the genus Cercopagis. C.(C.)pengoi was found in the Caspian Sea at salinities ranging from 1 to 13 PSU (Rivier 1967), in the Azov Sea at salinities up to 10 PSU (Mordukhai-Boltovskoi, 1961), in the Gebergin Lake at salinities ranging from 3 to 14 PSU (Valkanov, 1951, 1957), in the Dniepr-Bug estuary between 0 and 3.8 PSU (Markovsky 1954), and in the Tsimlyansk Reservoir ranging from 2.5 to 4 PSU (Glamazda, 1971). In the Baltic Sea, C.(C.)pengoi was found at salinities ranging from 0.5 to 7 PSU (Panov, unpubl.). In the Aral Sea C.(C.)pengoi was found at salinities up to 11 PSU (Rivier 1967), but has become extinct here because of a dramatic increase in salinities in the sea during last decades. In fresh water C.(C.)pengoi was recorded in the Dniepr River reservoirs: Kievskoe, Kremenchugskoe, Dnieprodzerzhinskoe, and Kahovskoe (Gusinskaya, 1989); and in the North American Great Lakes (MacIsaac et al., 1999; Ojaveer et al., 2001).
Relation to temperature. Eurythermic species
In the Caspian Sea, Cercopagis (Cercopagis) pengoi is not found in the plankton during winter. In the Northern and Middle Caspian Sea, parthenogenetic females first appear in the plankton at water temperatures between 15 and 17^�C (Rivier, 1967). In the Baltic Sea, C.(C.)pengoi appears in the plankton during first week of July with water temperatures above 15^�C (Krylov et al. 1999; Litvinchuk et al. 2001). In Lake Ontario, C.(C.)pengoi was found at temperatures between 17.4 and 23.9^�C (M�cIsaac et al., 1999). During autumn C.(C.)pengoi was present in the zooplankton at relatively low temperatures. In the Baltic Sea, C.(C.)pengoi was present in the zooplankton in first week of October at water temperatures of 8^�C (Krylov et al. 1999).
Vertical distribution. Eurybathic species
Cercopagis (Cercopagis) pengoi is a typical pelagic species. In the Northern Caspian Sea, C.(C.) pengoi (mainly form �gracillima�, which comprises up to 70% of the population) is most abundant in central areas at depths of 15-30 m. In northern areas of the Middle Caspian Sea (Cape Sagandyk) C.(C.)pengoi occurs at the depths of 50-100 m and is much less abundant. In the Middle Caspian Sea, C.(C.)pengoi is found at depths of 14-300 m, with maximum abundance at 100 m and minimum abundance at 300 m (Rivier, 1967).
Relation to oxygen conditions. Information is not available
Relation to fluctuations of the sea level. Information is not available

Feeding

Feeding type. Heterotrophic
Feeding behavior. Members of the family Cercopagidae are active predators. Cercopagids capture prey (mainly small plankton crustaceans) with the first pair of thoracic legs (thoracopods I), retain prey by other three pairs of thoracic legs (thoracopods II-IV), crush its cuticle by mandibles, and suck the prey body contents. Detailed information on feeding behavior of C.(C.) pengoi is not available.
Food spectrum. Information is not available
Supply of food. Information is not available
Quantitative characteristics of feeding. Information is not available.

Reproduction

Reproduction type. Parthenogenesis and gamogenesis
As other cladoceran crustaceans, Cercopagis (Cercopagis) pengoi possesses two patterns of reproduction, parthenogenesis and gamogenesis (sexual). Parthenogenesis prevails during periods of rapid population growth. In the Caspian Sea, sexual reproduction is more typical at the last stages of population growth, and results in the production of resting eggs. During this period, parthenogenetic females produce males and gamogenetic females, which are morphologically different. Details of development of parthenogenetic and resting eggs in C.(C.) pengoi are available in the literature (Rivier 1967, 1969, 1998).
Reproduction areas. Specific areas of reproduction in Cercopagis (Cercopagis) pengoi are not present in the Caspian Sea
Terms of reproduction. Cercopagids reproduce parthenogenetically during the whole period of their presence in the zooplankton. Sexual reproduction in Cercopagis (Cercopagis) pengoi occurs mainly during late summer and autumn in the Caspian Sea, but beyond its native range, in the Baltic Sea, sexual reproduction in C.(C.) pengoi was recorded during the whole period of its presence in the zooplankton (Krylov, Panov, 1998; Litvinchuk et al. 2001).
Fecundity. Fecundity of Cercopagis (Cercopagis) pengoi in the Caspian Sea averaged 13-20 embryos per parthenogenetic female (Rivier, 1967). In Gebergin Lake maximal fecundity was 10 embryos (Valkanov, 1951), and in Lake Ontario 8 embryos per female (MacIsaac et al. 1999). Fecundity was found maximal in specimens from the first generation, likely hatched from resting eggs. In C.(C.) pengoi from the Gulf of Finland (Baltic Sea) population, the maximal fecundity of 24 embryos per female was recorded in early July, which is absolute maximum for this species, and by August maximal fecundity declined up to 12 embryos per parthenogenetic female (Litvinchuk, 2001).
Fecundity of gamogenetic females is lower than that of parthenogenetic females. Most gamogenetic females in the Caspian Sea carried one resting egg, and females with 2 resting eggs were rare. In Lake Ontario, most gamogenetic females, around 80%, also carried one resting egg, and 18% had two egg broods. Only one specimen carried 3 resting eggs (Grigirovich et al. 2000). Gamogenetic females in the Baltic Sea population were found to be most fecund. Most gamogenetic females (94%) carried two resting eggs, females with one or three resting eggs in the brood pouch were rare. Sizes of resting eggs tended to be smaller with increasing clutch size (Krylov, Panov, 1998). Drawings by I.K.Rivier of gamogenetic females from the Baltic Sea population, carrying 1, 2 and 3 resting eggs are available at the GAAS web site (http://www.zin.ru/projects/invasions/gaas/cerpen_i.htm).
Limiting factors. Water temperature is likely to be the main factor, limiting hatching in Cercopagis (Cercopagis) pengoi. Hatching of juvenile C.(C.) pengoi from resting eggs occurs in late spring and early summer, when the period of reproduction terminates. Feeding conditions is most likely the main factor affecting fecundity in C.(C.) pengoi, but quantitative data are not available.

Life history and development

Life-history stages. Parthenogenetic reproduction during favorable seasons for growth in C. (C.) pengoi typically consists of the production of successive broods of parthenogenetic eggs, which develop into parthenogenetic females. At certain times, normally in late summer and autumn, parthenogenetic females produce eggs that develop into males and gamogenetic females. After copulation, fertilized eggs in gamogenetic females develop into diapausing embryos (resting eggs), which are released and sink out of the water column. Most likely, resting eggs sink to the bottom sediments where they remain until development resumes the following year, at time correlated with rising temperatures. Parthenogenetic females of the first generation of C. (C.) pengoi, hatch from resting eggs, and are anatomically distinct from parthenogenetic females of following generations. They resemble �.(Apagis) ossiani M.-Bolt., which are characterized by 4 pairs of caudal spines, a significantly shortened caudal process without a loop and maximal fecundity (Simm and Ojaveer, 1999; Rivier 2000; Grigorovich et al., 2000; Rivier unpubl.).
Relation to environmental factors. Information is not available
Age of maturity. Exact data on age of maturity in the first and following generations of C. (C.) pengoi are not available. Newborn instars I of parthenogenetic females already have clearly visible large ova in the ovaries. Also, before hatching of developed parthenogenetic embryos from the brood pouch, ova of the new generation are released under the placenta in the brood pouch (Rivier, 1967, 1969). Development time of embryos and instars in C.(C.) pengoi is not known.
Thermal conditions of development. In Northern and Middle Caspian Sea, the first generation of C. (C.) pengoi appears in zooplankton at temperatures of 15-17^�C (Rivier, 1967).
Quantitative characteristics of growth. Information is not available

Structural and functional population characteristics

Sex ratio. In the Caspian Sea, the population of Cercopagis (Cercopagis ) pengoi consists mainly of parthenogenetic females, while males and gamogenetic females are rare. In contrast, in Lake Ontario and Baltic Sea, males and gamogenetic females are abundant during the summer, which can be attributed to the adaptation to, and successful colonization of new habitats (Krylov, Panov, 1998; Grigorovich et al. 2000).
Age-size structure. Typically, instar III parthenogenetic females are prevalent in the population of C.(C.) pengoi, while instar I and instar II parthenogenetic females are less common. Instar I-III males and gamogenetic females can be also found, but they are very rare in the Caspian Sea population. Largest animals were found in the Baltic Sea, medium animals in the Caspian Sea, and smallest animals in Lake Ontario. However, caudal process length was minimal in C. (C.) pengoi from the Caspian population.
Selected morphometric characteristics of Cercopagis (Cercopagis) pengoi in Caspian Sea, Lake Ontario, Baltic Sea (modified from Grigorovich et al. 2000). Instar I-III parthenogenetic females are designated as pI-pIII, instar I-III gamogenetic females as gI-gIII, instar I-III males as mI-mIII.

Water Body	Instar Sex	N	Body Length, mm	Brood pouch Size, mm	Caudal process Length, mm
Caspian Sea
	pIII	31	1.73	1.70	7.48
	pII	6	1.51	1.09	7.19
	pI	1	1.10	0.80	7.60
Baltic Sea
	pIII	22	1.99	1.54	9.65
	pII	7	1.53	1.22	7.83
	gIII	4	1.90	1.20	-
	mIII	2	1.60	-	-
	mI	4	1.10	-	4.7
Lake Ontario
	pIII	395	1.45	0.84	8.57
	pII	171	1.29	0.55	7.66
	pI	42	1.02	0.25	6.26
	gIII	42	1.58	0.83	8.81
	gII	12	1.34	0.68	7.74
	gI	45	1.00	0.19	6.27
	mIII	30	1.37	-	5.40
	mII	18	1.15	-	4.82
	mI	9	0.98	-	4.45

Regression models relating body mass (W in mg) of sugar-formalin-preserved Cercopagis (Cercopagis) pengoi from Lake Ontario to length (L, in mm) and instar stage (I) (modified from Grigorovich et al. 2000).

Model Number	Description	Equation
1	all animals	logW = 0.175 + 1.631 logL + 0.131I
2	males only	logW = 0.224 + 3.255 logL
3	females only	logW = 0.214 + 1.279 logL + 0.151I

Quantitative characteristics..During 1962-1964, maximal abundance of Cercopagis (Cercopagis) pengoi in the Northern Caspian Sea was documented in July and early August, averaging several dozens of individuals per cubic meter. By October, C. (C.) pengoi disappeared from the zooplankton. In the Southern Caspian Sea in late September at water temperature of 22^�C, it was present in zooplankton at low densities (2-4 ind/m3) (I.K.Rivier, unpubl.).
During 1998-2000, in the western part of the Northern Caspian Sea (sandbank Malaya Zhemchuzhnaya area), maximal abundance of C.(C.) pengoi was documented during September and averaged concentrations of 110 ind./m3 (juveniles contributed over 70% of total population density). Comparatively high densities of C.(C.) pengoi, up to 55 ind./m3, were found in the Island Tuleniy area. Minimal densities of C.(C.) pengoi, (9 ind./ m3), were documented in the area between sandbanks Malaya Zhemchuzhnaya and Rakushechnaya Gorbachek. Moderate densities of C. (C.) pengoi, 21 and 29 ind./m3, were found in the sandbank Tuleniya area and Setnoi Oseredok, respectively. These areas were characterized by shallow depths, ranging from 3.6 m to 4.9 m, with maximal depth of 9.2 m. During the summer, in June 1999 and August 1998, C. (C.) pengoi was rare and only a few specimens were found. During 1998-1999, C.(C.) pengoi was found at low densities (0.4-1.0 ind./m3) only in the area of sandbanks Tuleniya and Large Zhemchuzhnaya at depths of 20-26 m. It was also found in the southeastern part of Northern Caspian Sea, in the area adjacent to the Middle Caspian (depth 43 m), at low densities (2 ind./ m3). During the autumn of 1998-1999 and summer of 2000, C.(C.) pengoi was not found in the zooplankton (L.I.Tarasova, unpubl.).
Population trends. For the Caspian Sea population of Cercopagis (Cercopagis) pengoi information on changes in species abundance over time is not available.

Interspecific relations

Abundance of Cercopagis (Cercopagis) pengoi in the Caspian Sea is strongly controlled by fish predation, which is likely the main cause of comparatively low densities of this species in the zooplankton. In 1998-2000, C.(C.) pengoi was found in fish stomachs of planktivorous fish, mainly in western part of the Northern Caspian Sea at depths of 2-32 m. North of Kulaly Island and Khohlatsky area, stomach contents in Clupeonella cultriventris and Atherina boyeri caspia consisted primarily of C.(C.) pengoi. Typically, proportion of C.(C.)pengoi in fish diets ranged in different fish from 0.01 to 11.07%, while frequency of C.(C.)pengoi occurrence in fish stomachs was comparatively high (M.M.Elizarenko, unpubl.).

Fish species
	Years
	1998				1999		2000
	June		August		June		June		September
	P	F	P	F	P	F	P	F	P	F
Clupeonella cultriventris (Common kilka)	0,16	16,7	8,79	46,4	2,79	16,8	0,60	19,4	8,50	28,6
Atherina boyeri caspia (Caspian silverside)	�	�	6,88	44,1	0,56	11,4	1,25	16,4	0,04	2,2
Alosa caspia (Caspian shad)	�	�	11,70	61,5	�	�	�	�	6,39	40,7
Alosa saposchnikowii (Big-eye shad)	�	�	10,90	35,3	�	�	�	�	0,01	3,6

 

Impact on the Ecosystem

Cercopagis (Cercopagis) pengoi is a native species for the Caspian Sea ecosystem and its abundance here is under intense control from fish predation. However, one may suppose that �the fishing net�s plague�, �when suddenly all the fishing nets at a vast distance dye during one day being ill by a net�s illness, a special algae� (Khlebnikov 1990) could be attributed to C. (C.) pengoi biofouling. �The fishing net�s plague� was well known among the Caspian Sea fishermen at the beginning of the 20th century. In the Gulf of Finland (Baltic Sea) coastal areas, fish catches declined because of biofouling of fishnets by paste from C. (C.) pengoi (Panov et al. 1999; Website GAAS at http://www.zin.ru/projects/invasions/gaas/cerpen.htm#impacts). Recently C.(C.)pengoi was included in the list of 100 of the World�s worst invasive alien species (Global Invasive Species Database, http://www.issg.org/database).

Importance of species to bioresources production of the Caspian Sea

Economic significance of species. No economic significance, but as nuisance species can negatively affect fishing
Human impact/Threats. Drastic decline in abundance of Cercopagis (Cercopagis) pengoi in the Caspian Sea is possible in future because of predation by the invasive North-American ctenophore Mnemiopsis leidyi. Complete extinction of C.(C.)pengoi is unlikely, because of a large pool of resting eggs in the Caspian Sea bottom sediments, which can remain viable for decades.
Conservation measures. Not required

References

Glamazda, V.V. 1971. On the occurrence of Cercopagis pengoi (Ostr.) in the Tsimlyansk Reservoir. Gidrobiol. Zhur. 7(3): 70-71 (in Russian).
Grigorovich I.A., MacIsaac H.J., Rivier I.K, Aladin N.V., Panov V.E. Comparative biology of the predatory cladoceran Cercopagis pengoi from Lake Ontario, Baltic Sea and Caspian Sea. Arch. Hydrobiol. 149 (1): 23-50.
Gusynskaya S.L. 1989. Pelagic zooplankton. In. Scherbak, G.I. (ed.): Invertebrates and fishes of the River Dnieper and its reservoirs. Naukova Dumka, Kiev, pp. 21-44 (in Russian).
Khlebnikov, V. 1990. [Esir (1918-1919)]. p. 71-83 in: Velimir Khlebnikov. Selected prose. Sovremennik, Leningrad (in Russian).
Krylov P.I., Panov V.E., 1998. Resting eggs in the life cycle of Cercopagis pengoi, a recent invader of the Baltic Sea. - Evolutionary and ecological aspects of crustacean diapause. Arch. Hydrobiol. Spec. Issues Advanc. Limnol. 52: 383-392.
Krylov P.I., Bychenkov D.E., Panov V.E., Rodionova N.V., Telesh I.V., 1999. Distribution and seasonal dynamics of the Ponto-Caspian invader, Cercopagis pengoi (Crustacea, Cladocera), in the Neva Estuary (Gulf of Finland). Hydrobiologia 393 (Dev. Hydrobiol. 135): 227-232.
Litvinchuk L.F., Rivier I.K., Panov V.E. 2001. Dynamics of abundance, structure of population and fecundity of Ponto-Caspian predaceous cladoceran, Cercopagis pengoi (Ostroumov, 1891) (Polyphemoidea, Cercopagidae), in the eastern Gulf of Finland, the Baltic Sea. Biology of Inland Waters 1: 57-62.
MacIsaac H.J., Grigorovich I.A., Hoyle J.A., Yan N.D., and Panov V.E. 1999. Invasion of Lake Ontario by the Ponto-Caspian cladoceran predator Cercopagis pengoi. Can. J.Fish.Aquat.Sci. 56: 1-5.
Mordukhai-Boltovskoi, Ph.D., Rivier, I.K., 1971. A brief survey of the ecology and biology of the Caspian Polyphemoidea. - Marine Biology 8: 160-169.
Ojaveer H., Kuhns L.A., Barbiero R.P., and Tuchman M.L. 2001. Distribution and population characteristics of Cercopagis pengoi in Lake Ontario. J.Great Lakes Res. 27 (1): 10-18.
Ostroumov, A. 1892. Report on participation in research trip on the Azov Sea on board of transport ship �Kazbek� in summer, 1891. Mem. Imp. Acad. Sci. St.Petersburg/Suppl.69(6): 1-19 (in Russian).
Panov, V. E., P. I. Krylov & I. V. Telesh 1999. The St. Petersburg harbour profile. - In: (Gollasch, S. & E. Leppäkoski, eds) Initial risk assessment of alien species in Nordic coastal waters. Nord 1999:8. Nordic Council of Ministers, Copenhagen: 225-244.
Rivier, I.K. 1967. Ecology and biology of polyphemids in the Caspian Sea. Candidate Dissertation. �Inst. of Biology of Inland Waters, Acad.Sci. of the USSR, Borok. (in Russian).
Rivier, I.K. 1998. The predatory Cladocera (Onychopoda: Podonidae, Polyphemidae, Cercopagidae) and Leptodorida of the world. Backhuys Publishing, Leiden, 214 pp.
Sars, G.O. 1897. Pelagic Entomostraca of the Caspian Sea. Ann.Mus.Zool.Imp.Acad.Sci. St.Petersburg 2: 1-73, pls.I-VIII.
Simm, M., Ojaveer, H. 1999. Occurrence of different morphological forms of Cercopagis in the Baltic Sea. Proc.Estonian Acad.Sci.Biol.Ecol.48:169-172.
Valkanov, A. 1951. Study of Cercopagis pengoi (Ostr.) (Cladocera, Polyphemidae). Tr. Morsk. biol. St. Varna. Vol. 16: 65-81 (in Bulg.).
Valkanov, A. 1957. Katalog unserer Schwarzmeerfauna. Tr. Morsk. biol. St. Varna. Vol. 19: 1-63 (in Bulg.).

Links to other sources in the INTERNET

Illustrated Database at the GAAS web site http://www.zin.ru/projects/invasions/gaas/aa_idb.htm
Baltic Sea Alien Species Database http://www.ku.lt/nemo/cercopag.htm
EPA (USA) web site http://www.epa.gov/glnpo/monitoring/exotics/cercopagis.html
Dr MacIsaac�s Laboratory web site in Canada http://www.cs.uwindsor.ca/users/h/hughm/private/cercopagis.html

Compiled by:

Irena K. Rivier, Institute for Biology of Inland Water RAS, Borok, Russia
Vadim E.Panov, Zoological Institute RAS, St.Petersburg, Russia
Larisa I.Tarasova, CaspNIRKH,Astrakhan, Russia
Marina M.Elizarenko, CaspNIRKH, Astrakhan, Russia

Acknowledgements:

Authors are grateful to Dr. Valentina Belyaeva (CaspNIRKH, Astrakhan, Russia) and Dr. Piotr Krylov (Zoological Institute RAS, St.Petersburg, Russia) for valuable comments, and to Dr. Carol Lee (University of Wisconsin, Madison, USA) for editing of English version of the entry.