Determining the Ploidy and Resultant Reproductive Capability of Artificially Spawned and Wild Caught Asian Carp

Science Center Objects

The invasive grass carp and black carp are artificially spawned to produce triploids, which means they have three sets of chromosomes and are sterile. WARC scientists invented an early ploidy prediction process for produced fry, and a post-mortem assessment method for carp caught either in the wild or sold and hauled live to other states. 

Determining the Ploidy and Resultant Reproductive Capability of Artificially Spawned and Wild Caught Asian Carp

Feral caught grass carp

The Science Issue and Relevance: Invasive grass carp (Ctenopharyngodon idella) have spread throughout the Mississippi River and are threatening the Great Lakes Ecosystem. Increasing captures of invasive black carp (Mylopharyngodon piceus) in the middle and lower Mississippi River and tributaries raise concerns about them establishing in the wild. Grass carp are voracious feeders that can strip native vegetation and out-compete native fish. Black carp are molluscivores and pose a threat to federally listed riverine mollusks. Both of these Asian carp species are artificially spawned to produce triploids, which have three sets of chromosomes and are reproductively sterile. This inability to breed is the basis of a commercial market, and nearly 5 million triploid grass carp have been sold to control aquatic vegetation in the last ten years. Triploid black carp are sold to manage unwanted snails. Though aquaculture farms have developed methods to induce triploidy, 100% triploid batches are often elusive. 

Methodology for Addressing the Issue: This laboratory has invented an early ploidy prediction process for produced fry, and a post-mortem assessment method for carp that are either caught in the wild or being sold and hauled live to other states. For fry, cell suspensions are made from 50 individuals. For hauled juveniles and adult fish from the wild, cells are extracted from eyeballs. Nuclei are then stained with a fluorescent DNA dye. By comparing the amount of DNA in the experimental cells with that of a known control species, diploidy can be distinguished from triploidy.

Determining the Ploidy and Resultant Reproductive Capability of Artificially Spawned and Wild Caught Asian Carp

Extracting cells from eyeballs of feral grass carp

Future Steps: Currently we are working with a state partner and among 4 laboratories around the country in developing a standardized protocol for assessing ploidy from the small triploid carp that are intercepted from live haul trucks on U.S. public roadways.  

Determining the Ploidy and Resultant Reproductive Capability of Artificially Spawned and Wild Caught Asian Carp

Flow cytometry histograms showing DNA from carp eye cells (arrowhead) and channel catfish blood (arrow) stained fluorescently for determining relative DNA content. Catfish has a 2.54 pg  genome size, thus the carp was triploid (~3.0 pg).