Asian Carp Hybridization: Prevalence, Distribution, and Post-Zygotic Success in the Mississippi River Basin

Asian carp hybridization is known to occur beyond the F₁ generation in the United States, but the distribution, growth, and condition of hybrids is unknown.  We created a powerful diagnostic SNP assay to detect multi-generational Asian carp hybrids within the Mississippi River Basin and their range in China.   We collected 3100 putative bighead carp, silver carp and their hybrids from nine separate geographic locations distributed throughout the Mississippi River Basin.  For all fish collected, we recorded total length and weight to estimate condition, gonad weight (GSI), removed a fin clip for genetic identification, and removed and sectioned a postcleithrum to determine age and growth.  Known age of each fish and genotype was used to infer hybrid classification at birth year.  Advanced hybridization was evident at all locations sampled (43%).  An increase in hybrid proportions in younger cohorts provided evidence of a hybrid swarm perpetuating over time.  Early generation hybrids (F₁, SVBx₁, BHBx₁) exhibited significantly lower condition (p=0.05) than parents of either species or later generation backcrosses demonstrating a hybrid disadvantage in recently hybridized individuals.  Our in-depth discovery of Asian carp hybrid dynamics within the Mississippi River Basin has management implications in regards to life history and potential control efforts.