Fishhook waterflea
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| Fishhook Waterflea | ||||||||||||||||||||
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 Cercopagis pengoi (above)
Bythotrephes sp. (below) |
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| Cercopagis pengoi |
The Fishhook Waterflea (Cercopagis pengoi) is a species of water flea native to Ponto-Aralo-Caspian basin in South Eastern Europe at the meeting point of the Middle East, Europe, and Asia. This species is similar to Bythotrephes longimanus, and occurs in estuaries, lakes, marine habitats, water courses, and wetland areas.
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[edit] Description
The most pronounced parts of the body are: the head, the second pair of quadriceps, four pairs of thoracic legs (thoracopodsI-IV), abdomen, caudal process, and a brood pouch in females. The head is essentially composed of a large single eye, where the amount of black pigment makes less than one half of the diameter of the eye. The second antenna is a large appendage containing of two branches - the endopod and exopod. The first pair of thoracic legs (thoracopods I) is 3-4 times longer than the second one. Abdomen length is equal to length of the rest of body, and spines are large, equal to 2-3 diameters of caudal process (Mordukhai-Boltovskoi & Rivier, 1987; Rivier 1998). Parthenogenic females of the first generation of C. pengoi that hatch from resting eggs are anatomically distinct from parthenogenic females of following generations. They have a short straight caudal spine unlike the characteristically looped caudal spine of parthenogenically-produced individuals (Simm & Ojaveer 1999). C. pengoi possesses a high degree of regional variability in morphology. Largest adult parthenogentic females are found in the Baltic Sea (mean body length 1.99 mm), while those in the Caspian Sea and in Lake Ontario are smaller (1.73 and 1.45 mm, respectively). Caudal processes are largest in the instar III parthenogenic females from the Baltic Sea (mean length 9.65 mm), medium in Lake Ontario (8.57mm), and shortest in females from the Caspian Sea (7.48 mm). However, relative to body length, the length of caudal process is largest in populations from Lake Ontario (mean 5.9 mm), medium in the Baltic (4.9 mm), and smallest in the Caspian populations (4.3 mm) (Grigorovich et al. 2000).
[edit] Habitat description
C. pengoi is euryhaline (having a wide tolerance to salinity) and eurythermic (can tolerate a wide range of temperatures) species, occurring in both brackish (up to 17‰) and fresh waters, as well as highly variable temperatures (3 – 38 ºC; c.f. Gorokhova et al. 2000). Usually highest population densities are found at summer temperatures (16 – 26 ºC) and at salinities of up to 10 ‰ (Mordukhai-Boltovskoi & Rivier, 1987; Rivier, 1998). Both in the Caspian Sea (Rivier, 1998) and Lake Ontario (Ojaveer et al. 2001) C. pengoi abundance increases with distance from shore suggesting that this is a typical pelagic (fish and animals that live in the open sea, away from the sea bottom) species.
[edit] Geographical range
Native range: Southern Europe - Ponto-Aralo-Caspian basin, i.e. Caspian, Black and Azov seas and small coastal lakes in this area (Mordukhai-Boltovskoi & Rivier, 1987; Rivier 1998). Known introduced range: waterways and reservoirs in the Eastern Europe, Baltic Sea, Laurentian Great Lakes, Finger Lakes (North America) (Leppäkoski & Olenin, 2000; Therriault et al. 2002; Vanderploeg et al. 2002).
[edit] Spread
The waterflea has spread from my native range and become invasive in some waterways of Eastern Europe and in the Baltic Sea. It has been introduced to the Great Lakes of North America, quickly became established and now is increasing its range and abundance. This species is voracious predator and may compete with other planktivorous invertebrates and vertebrates. Through this competition, C. pengoi has the potential to affect the abundance and condition of zooplanktivorous fish and fish larvae; this species also interferes with fisheries by clogging nets and fishing gears.
[edit] General impacts
C. pengoi is a potential competitor with young stages of planktivorous fish for herbivorous zooplankton (Vanderploeg et al. 2002). Several lines of evidence indicate that C. pengoi may affect resident zooplankton communities by selective predation: Lake Ontario (Benoit et al. 2002); Gulf of Riga (Ojaveer et al. 1999, 2004); Gulf of Finland (Uitto et al. 1999). Such changes may result in decreased grazing pressure on phytoplankton and enhanced algal blooms. It is, however, difficult to study food competition between small fish and C. pengoi because of the lack of feeding studies on the latter. On the other hand, zooplanktivorous fish both in the Baltic (Antsulevich and Välipakka 2000; Gorokhova et al. 2004; Ojaveer et al. 2004) and in the Great Lakes (Bushnoe et al. 2003) have been reported to prey on C. pengoi implying that it has become a new food source, particularly for larger fish. Moreover, this large cladoceran tends to attach to fishing gears, clog nets and trawls, causing problems and substantial economic losses for fishermen (Leppäkoski & Olenin, 2000; ICES, 2002).
The paucity of ecological studies on C. pengoi is in part due to the difficulty of culturing Cercopagis handling it and using in experiments.
Invasion pathways to new locations Ship ballast water
Local dispersal methods Boat: Both in live well and on fishing lines.
Management information Preventative measures: Prompted by the explosive increase of ship-borne exotic species in the Great Lakes, in May 1993 the USA implemented a regulation that requires inbound vessels to exchange freshwater/ estuarine ballast with highly saline oceanic water (Ricciardi and MacIssac 2002). In theory, this procedure should greatly reduce the risk of invasion because freshwater organisms would be purged or killed by seawater, and would be replaced by marine organisms that would not survive if released into the freshwaters. However, the recent invasion of C. pengoi draws concern because it was apparently introduced after implementation of ballast water regulations. The authors believe that "without more effective ballast water control, continued invasion and transformation of West European and North American inland waters by Ponto-Caspian species is highly probable."
The following measures could prevent further spread of this and other species with similar ecology: 1) Do not release bait or bait water into water body or transport from one water body to another. 2) Following good containment measures is important in controlling the spread of adult C. pengoi, but resting eggs are capable of surviving desiccation and freezing (even for periods of several years). 3) Rinsing boat and equipment with hot water (>40°C), high-pressure water spray, or drying boat and equipment for at least 5 days before re-entering water body will help to control the spread of adult C. pengoi. 4) Thoroughly draining and cleaning motor; bilge, transom, and live wells; bait buckets; and fishing apparatus and gear will help to control the spread of adult C. pengoi and resting eggs (Crosier and Molloy (UNDATED))
[edit] Nutrition
Cercopagids capture their prey with the thoracopods I, retain it by thoracopods II-IV, crush its cuticle by mandibles, and suck the prey body contents (Mordukhai-Boltovskoi & Rivier, 1987; Rivier, 1998). Detailed information on feeding behavior of C. pengoi is not available. Diet includes mainly small crustaceans, both micro- and mesozooplankton (Mordukhai-Boltovskoi, 1968; Rivier, 1998; Laxson et al. 2003; Gorokhova et al. 2005).
[edit] Reproduction
As many other cladocerans, C. pengoi is a cyclic parthenogen. It reproduces parthenogenically during the summer and gametogenically later in the year. The parthenogenically-produced young develop in a fluid-filled dorsal brood pouch that ruptures to release the young. In late summer and autumn, parthenogenic females produce eggs that develop into males and gametogenic females, which copulate. Gametogenic reproduction results in resting eggs that are released when the brood pouch ruptures and which overwinter in the sediment. After a refractory period development proceeds and neonates hatch in spring-summer, depending on local temperatures, to re-found the population (Mordukhai-Boltovskoi & Rivier, 1987; Rivier, 1998). Sexual females are reproductive only at instars II and III, producing 1-4 resting eggs, while parthenogenic females produce between 1 and 24 embryos; average clutch size decreases gradually from instar I to instar III and from early to late stage of embryonic development (Grigorovich et al. 2000).
[edit] Lifecycle stages
Females (both parthenogenic and gametogenic) and males possess 3 life-history stages (instars), differing by number of spines (barbs) on the caudal process. At each molt, the animal sheds its exoskeleton to the base of the caudal process. A new pair of proximal barbs and the growth of an intercalary segment are inserted between the existing tail spine and the body. The newborn parthenogenic females (instar I) have one pair of barbs on the caudal process, compact oval embryos in the brood pouch without a pointed apex. The second stage (instar II) has two pairs of barbs and the mature stage (instar III) of the parthenogenic female has a large brood pouch with a pointed apex housing embryos. In males at this stage paired penes behind the last thoracic legs and a toothed hook on the first pair of legs are developed (Mordukhai-Boltovskoi & Rivier, 1987; Rivier 1998). Parthenogenic females of the first generation of C. pengoi proceed through 3 moult yielding 4 pairs of proximal barbs on the caudal process unlike the females of following generations that undergo 2 molts to reach adulthood (Simm & Ojaveer 1999).
This species has been nominated as among 100 of the "World's Worst" invaders
Compiled by: National Biological Information Infrastructure (NBII) and Invasive Species Specialist Group (ISSG) Kerry McPhedran and Igor A. Grigorovich. Great Lakes Institute for Environmental Research, University of Windsor, Canada
[edit] References
Public Domain Information From:
- The IUCN/SSC Invasive Species Specialist Group (ISSG) (http://www.issg.org), Global Invesive Species Database: http://www.issg.org/database/welcome/,
- Related Disclaimer: http://www.issg.org/database/welcome/disclaimer.asp
