Abstract
Monitoring ichthyoplankton is useful for identifying reproductive fronts and spawning locations of bigheaded carps (Hypophthalmichthys spp.). Unfortunately, sorting and identifying ichthyoplankton to monitor for bigheaded carp reproduction is time consuming and expensive. Traditional methods require frequent egg-larvae sampling, sorting of all samples to obtain presumptively identified bigheaded carp, and genetic validation of presumptively identified eggs. Quantitative PCR (qPCR) has the potential to streamline this process by identifying samples that likely do or do not contain a target species. Our objective was to develop a genetic screening tool using qPCR with the duplex assays SCTM4/5 and BHTM1/2 to prioritize samples that have a higher likelihood of containing bigheaded carp eggs or larvae. We used tandem ichthyoplankton samples collected for monitoring bigheaded carps in the Upper Mississippi, Illinois, and St. Croix rivers to evaluate the effectiveness of qPCR as a screening tool. Samples with > 10,000 copies of DNA had 100% occurrence of bigheaded carp eggs or larvae in the traditionally sorted samples, whereas samples with < 10 copies of DNA had 0% occurrence of ichthyoplankton from these invasive species. We used a logistic regression model to calculate the probability of finding bigheaded carp eggs or larvae based upon the number of DNA copies; 406 copies corresponded with a 50% probability of having bigheaded carp ichthyoplankton present in a sample. These data can be used to inform management actions (i.e., control, containment) for these invasive fishes, and this tool could be adapted for monitoring for reproduction of other aquatic invasive species.
Highlights
Bighead Carp (Hypophthalmichthys nobilis) and Silver Carp (H. molitrix), collectively referred to as bigheaded carps, are invasive fishes originating from eastern Asia that were introduced to North American waters beginning in the 1970s
Our objective was to develop a genetic screening tool using Quantitative PCR (qPCR) to prioritize samples for processing that have a higher likelihood of containing bigheaded carp eggs or larvae
Samples that had a combined total of \ 10 copies (n = 10) had 0% occurrence of bigheaded carp eggs or larvae in the traditionally sorted sample
Summary
Bighead Carp (Hypophthalmichthys nobilis) and Silver Carp (H. molitrix), collectively referred to as bigheaded carps, are invasive fishes originating from eastern Asia that were introduced to North American waters beginning in the 1970s. Bigheaded carps have become established across large portions of the Mississippi, Missouri, and Ohio River drainages, and are poised to establish populations in the Great Lakes and the Upper Mississippi River and Ohio River basins. Their high consumptive demand, high reproductive and growth potential, migratory behavior and planktivorous nature make them well suited to compete with native fauna reliant on planktonic food resources, including most larval fishes (Kolar et al 2005; Fritts et al 2018). Managers must know when and where reproduction of bigheaded carp is occurring in invaded systems, especially near the invasion front, to efficiently and effectively contain and control populations
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