Bythotrephes longimanus

Distinguished from the congeneric fishhook water flea Cercopagis pengoi by its more robust spine lacking the prominent loop-like hook at the tip. The kinked spine of parthenogenetic individuals and straight spine of sexually produced individuals were formerly considered separate species (B. cederstroemi vs. B. longimanus), but genetic analysis confirms these as a single species with ecological morphs. Larger body size and more extensive barbing on spine separate adults from juveniles.

Adults less than 15 mm in length. Body with long abdominal spine (caudal process) averaging about 70% of total body length; spine bears one to three pairs of barbs in adults, one pair in juveniles. Spine morphology varies: straight and relatively shorter in sexually produced individuals, with a kink in the middle in parthenogenetically produced individuals. Single large eye, black or red. Pair of swimming antennae and four pairs of legs, with first pair modified for prey capture. Mandibles present for prey consumption. Females grow up to 8 times larger than males.

Freshwater lakes and waterbodies. Temperature tolerance 4–30°C, with preference for 10–24°C. Salinity tolerance 0.04–8.0‰, with preference for 0.04–0.4‰; distribution restricted in warmer, more saline waters. Pelagic zone dweller with diel vertical migration behavior. Habitat use influenced by basin morphometry, flushing rate, dissolved oxygen, pH, and lake trophic status. In invaded lakes, vertical distribution modified by predation risk from planktivorous fish.

Native to northern Europe and Asia, including parts of central Europe. Accidentally introduced to North America; first detected in Lake Ontario in 1982, subsequently spread throughout the Great Lakes and over 60 inland lakes in Ontario and the Midwest. Dispersal continues via ballast water, recreational boating equipment (fishing lines, nets, down-riggers), and river connections. Within Eurasia, distribution extends across the Commonwealth of Independent States with regional varieties (B. l. var. balticus, B. l. var. transcaucasicus, B. l. var. arcticus).

Active during ice-free season in temperate lakes. Cyclomorphosis produces distinct seasonal forms. Resting eggs enable survival through seasonally inhospitable conditions. Adults overwinter in some populations; emergence timing varies with temperature. In native range, occurrence and density vary with seasonal temperature changes.

Predatory, feeding on smaller planktonic organisms. Primary prey includes zooplankton such as Daphnia species and smaller crustaceans. Consumption rate of 10–20 prey organisms per day has been observed. Prey capture accomplished using modified first pair of legs; mandibles used for processing prey.

Cyclic parthenogenesis: alternating parthenogenetic and sexual reproduction. Parthenogenetic females produce offspring with kinked spines; sexually produced offspring have straight, relatively shorter spines. Two-year development in some populations; produces resting eggs that tolerate desiccation and passage through fish digestive tracts, facilitating dispersal. Overwinters as adults in some populations, as resting eggs in others.

Exhibits diel vertical migration, but with reduced amplitude compared to predictions from predator-avoidance hypothesis. Migration pattern modified by predation risk: stays higher in water column during day in lakes with cold-water planktivores (Coregonus spp.) to avoid overlap with hypolimnetic predators, resulting in smaller migration amplitude. Non-lethal effects on prey include induction of vertical migration and reduced growth rates in Daphnia species exposed to Bythotrephes kairomones.

Predatory zooplankter occupying mid-trophic level in pelagic food webs. Prey for planktivorous fish including Coregonus species; spine and barbs provide physical defense reducing vulnerability to small fish. Competes with native predatory cladocerans such as Leptodora kindtii for prey and habitat. Invasion has caused declines in native zooplankton abundance and diversity, alterations in prey vertical distribution, and trophic cascades affecting phytoplankton communities and water clarity.

Significant invasive species of economic and ecological concern in North America. Disrupts freshwater ecosystems, reduces water quality, and impacts recreational fishing through competition with juvenile fish for zooplankton prey and alteration of food web structure. Spread facilitated by recreational boating and fishing equipment; eggs survive desiccation and fish consumption. Management concerns include ballast water treatment and cleaning of recreational equipment to prevent further spread.

• Cercopagis pengoiFishhook water flea, also invasive in Great Lakes; distinguished by more slender spine with prominent loop-like hook at tip rather than robust barbed spine of Bythotrephes
• Leptodora kindtiiNative predatory cladoceran with which Bythotrephes competes for prey and habitat; native to same invaded ecosystems and has declined following Bythotrephes establishment

• invasive species
• zooplankton
• predator
• Great Lakes
• cladoceran
• cyclic parthenogenesis
• diel vertical migration
• pelagic
• freshwater
• crustacean

• BugGuide
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• Catalogue of Life
• Zookeys | Blog - Part 3
• Pseudoscorpiones | Beetles In The Bush
• Patterns of Bythotrephes longimanus distribution relative to native macroinvertebrates and zooplankton prey
• Life History and Multiple Antipredator Defenses of an Invertebrate Pelagic Predator, Bythotrephes longimanus
• Bythotrephes longimanus in the Commonwealth of Independent States: variability, distribution and ecolog
• Evolution or Extinction: Might Zooplankton Adaptively Respond to the Novel Invasive Predator Bythotrephes longimanus?
• Modeling Bythotrephes longimanus invasions in the Great Lakes basin based on its European distribution
• Evolutionary change in metabolic rate of Daphnia pulicaria following invasion by the predator Bythotrephes longimanus
• Evolutionary change in metabolic rate of Daphnia pulicaria in response to the invasive predator Bythotrephes longimanus
• Modeling the establishment of invasive species: habitat and biotic interactions influencing the establishment of Bythotrephes longimanus
• Food limitation impacts life history of the predatory cladoceran Bythotrephes longimanus, an invader to North America
• LIFE HISTORY AND MULTIPLE ANTIPREDATOR DEFENSES OF AN INVERTEBRATE PELAGIC PREDATOR,BYTHOTREPHES LONGIMANUS
• Distribution patterns and predation risk of the coexisting cladocerans Bythotrephes longimanus and Leptodora kindtii in a large lake – Lake Constance
• Non‐lethal effect of the invasive predator Bythotrephes longimanus on Daphnia mendotae
• Uncoupling indicators of water quality due to the invasive zooplankter, Bythotrephes longimanus
• Modification of the diel vertical migration of Bythotrephes longimanus by the cold‐water planktivore, Coregonus artedi
• Leptodora kindtii Population Dynamics in the Island Region of Western Lake Erie before and after the Invasion of the Predacious Cladoceran Bythotrephes longimanus