Evidence of Black Carp Establishment in the Mississippi River

Black carp were introduced to the U.S. to control aquaculture pond snails and are listed as injurious due to their potential threat to endangered riverine mollusks.  The increasing frequency of black carp captures from the Mississippi River and tributaries has raised concerns that they may become established in the wild.  However, black carp reproduction and recruitment in U.S. rivers have not been documented.  We used otolith chemistry and determined ploidy of black carp collected from the Mississippi River and tributaries between 2011-2014 to assess occurrence of natural reproduction. We also estimated GSI, age and growth for each fish; gonad histology was used to identify mature individuals.  Eighteen of 19 individuals tested were diploid.  Fish ranged in size from 445-1380 mm and in weight from 1.1-34.5 kg.  Fish ages ranged from 2-16 years, with multiple year classes present.  All fish ≥ age 6 were sexually mature.  Otolith core δ¹⁸O and δ¹³C of diploid fish were indicative of natural reproduction and recruitment; the triploid individual had an otolith core isotopic composition indicative of aquaculture pond origin.  Otolith core Sr:Ca and δ¹⁸O data for diploid fish also indicated that black carp reproduction is not confined to the middle and lower Mississippi River, but has also occurred in the upper Mississippi and/or Illinois rivers.