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Montana Field Guide

Montana Field Guides

Fishhook Waterflea - Cercopagis pengoi

Aquatic Invasive Species
Exotic Species (not native to Montana)

Global Rank: G5
State Rank: SNA
* (see State Rank Reason below)

Agency Status


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State Rank Reason (see State Rank above)
A conservation status rank is not applicable because this species is not a suitable target for conservation activities as a result of being exotic or introduced.
General Description
The Fishhook Waterflea is a large cladoceran (zooplankton) with a long straight tail spine that is 2 to 4 times as long as its body, and has a fishhook like curve on the end of it.
Parthenogenically produced animals have kink in middle of their spine and sexually produced animals lack the kink. This species has not been found in any Montana waterbodies yet.

Diagnostic Characteristics
Body size from 1–3 mm in length without tail, 6–13 mm with tail; tail has three pairs of barbs and a characteristic loop near the end.

Range Comments
Native To: Black, Caspian, Azov, and Aral seas of Europe and Asia (Makarewicz et al. 2001).

Nonindigenous Range: Introduced into Lake Ontario in 1998, Lake Erie in 2002 (Presque Isle), Lake Huron in 2002 (USEPA 2008), Lake Michigan in 1999 (Charlebois 2001) and then the Finger Lakes (Canandaiga, Cayuga, Keuka, Cross, Otisco, Owasco, and Seneca lakes) of New York.

Summary of Observations Submitted for Montana
Number of Observations: 0

(Click on the following maps and charts to see full sized version) Map Help and Descriptions


(Observations spanning multiple months or years are excluded from time charts)

This species exhibits diurnal vertical migrations within lakes in its native range and feeds on other zooplankton (Benson et al. 2017).

The Fishhook spiny waterflea lives in brackish and freshwater lakes.

Food Habits
Cercopagis pengoi is a consumer of other zooplankton.

Cercopagis pengoi lives in brackish and freshwater lakes. It exhibits diurnal vertical migrations in its native range and feeds on other zooplankton (Benson et al. 2017). Its long spine makes it less palatable to planktivorous fish. For these reasons C. pengoi could have a serious effect on the food supply of planktivores.

Reproductive Characteristics
In addition to sexual reproduction, Cercopagis most commonly reproduces parthenogenically (asexually) during the summer, which allows it to quickly establish new populations with a relatively small seed population without the need for a large number of the smaller males along with females.

They can be easily transported to other drainage basins by various vectors, particularly if there are eggs still in the female's body (the barbed caudal spine allows attachment to ropes, fishing lines, waterfowl feathers, aquatic gear, vegetation and mud) (Benson et al. 2017). Resting eggs can hatch regardless of whether the carrier female is alive or dead. C. pengoi could have a serious effect on the food supply of planktivores.

Threats or Limiting Factors
C. pengoi, a free-swimming macroinvertebrate, would likely find suitable habitat throughout the reservoirs of Montana, except for the deepest waters of Flathead Lake. However, in the Great Lakes, population densities of the fishhook water flea increase with distance from shore, suggesting that this species may be able to occupy the entire Great Lakes region, including the deeper waters of Lake Superior, given sufficient time (USEPA 2008).

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Citation for data on this website:
Fishhook Waterflea — Cercopagis pengoi.  Montana Field Guide.  .  Retrieved on , from