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Grass carp Ctenopharyngodon idella, is an herbivorous fish originally brought to North America from Asia in 1963 to control nuisance aquatic vegetation. Since their arrival, detrimental alterations to aquatic ecosystems have sometimes occurred in waterways where they were initially stocked and into which they have escaped. The movements of grass carp from lentic systems into tributaries required for spawning is poorly understood, and understanding environmental conditions associated with upstream migrations may aid in management of the species. We stocked 43 fertile diploid and 43 sterile triploid grass carp implanted with acoustic transmitters into Truman Reservoir, Missouri, USA between January 2017 and October 2018 to characterize movements during spring and summer when spawning conditions occur. Twenty fish (11 diploid/9 triploid) exhibited upstream migration behavior in the Osage River, a major tributary, in 2018 and 2019. Migration primarily occurred in April and May, during high discharge events associated with increasing river stage when water temperatures were between 15 and 28°C. Observed migrations ranged from 3.0–108 river km in length, and six individuals were observed making multiple upstream migrations in one season. Eleven fish initiated upstream migrations while in the lentic main body of the reservoir. These findings provide some evidence for upstream migrations by diploid and triploid grass carp as well both lake and river residents. Evidence of similar upstream migration behavior by both diploid and triploid grass carp suggests that triploids may be suitable surrogates for diploids for study of movement ecology. Removal efforts in tributaries targeting periods of increasing river stage during spring may provide the best opportunity of encountering large concentrations of grass carp. [ABSTRACT FROM AUTHOR]

Substantial work has been conducted to estimate the river length required for recruitment of invasive Grass Carp Ctenopharyngodon idella and bigheaded carps (Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix); however, the distance upstream and size of stream required for spawning remain unclear. Adult Grass Carp are regularly captured in Harry S. Truman Reservoir, Missouri, although there have been only unconfirmed sightings of Silver Carp. Fertile diploid Grass Carp are used legally for vegetation control in Missouri; however, it is uncertain whether Grass Carp in Harry S. Truman Reservoir are the result of natural reproduction or escapees. We used ichthyoplankton tows and environmental DNA (eDNA) to investigate which carp species were present in the reservoir basin and to determine whether these carps were spawning in reservoir tributaries. Grass Carp eggs were collected in four of five tributaries during June 2014. We did not detect eggs, larvae, or eDNA of Bighead Carp or Silver Carp. The occurrence of Grass Carp eggs generally coincided with rapid increases in discharge and turbidity. These tributaries may be the smallest rivers worldwide in which spawning of Grass Carp has been documented. We infer from the developmental stages captured and the distance from the reservoir that sufficient river length exists for egg survival. These results have broad implications concerning the establishment of Grass Carp in other novel habitats, including other reservoirs and lake basins, smaller rivers, and the Laurentian Great Lakes ecosystem. [ABSTRACT FROM AUTHOR]