Asian Carp Hybridization: Prevalence, Distribution, and Fitness In the Mississippi River Basin

Outcomes of introgressive hybridization include genomic extinction of one or both parental species, decrease and extinction of species through genetic incompatibilities, or speciation through selection of adaptable characteristics.  Although interspecific hybridization among bighead and silver carp is known to occur beyond the F₁ generation in the United States, the evolutionary fate, rate, distribution, depth, growth, and condition of hybrids is unknown.  We have created powerful diagnostic SNP assays to detect multi-generational hybrids and directionality of hybridization in Asian carp within the Mississippi River Basin and China.   3500 putative bighead carp, silver carp and their hybrids were collected from eight separate geographic locations distributed throughout the Mississippi River Basin.  Total length and total weight were recorded to estimate condition, gonad weight for GSI, a fin clip removed for genetic identification, and a postcleithrum removed and sectioned to determine age and growth for all fish in the study.  Advanced hybridization was evident at all locations sampled and an increase in hybrid prevalence and gametic disequilibria in younger cohorts provides evidence of a hybrid swarm perpetuating over time.  Condition and growth vary between discernible hybrid generations and geographic location and a silver carp maternal bias exists contributing to the hybrid progeny.