Extreme olfactory sensitivity of silver and bighead carp to overlapping suites of 21-carbon steroids suggests that these species, and likely all other Cyprinoidei, employ them as pheromones.

Although well established that several fishes including goldfish in the suborder Cypinoidei within the family Cypriniformes use the maturation-inducing steroid 17,20ß-dihydroxy-pregn-4-ene-3-one (17,20ßP) and its metabolites as a priming pheromone which they detect with sensitivity and specificity, it is unclear whether and how other Cypriniformes might have evolved to do so. This study examined this question in the family Xenocyprididae. Using electro-olfactogram recording we tested the olfactory sensitivity of silver (Hypophthalmichthys molitrix) and bighead carp (H. nobilis) to a range of 213 steroids in 21 mixtures at 10-9M. While silver carp detected 6 of 21 mixtures, bighead carp detected 5 (p< 0.05). Silver carp were sensitive to 13 21-carbon steroids in these mixtures including 17,20ßP while bighead carp detected 9, including 8 detected by silver carp. This assortment of steroids overlapped that detected by goldfish (family Cyprinidae) but no non-Cyprinoid, suggesting common evolutionary origin and function with differences characteristic of species-specificity.

Histopathological evaluation of the infection elicited by three species of Myxobolus (Cnidaria: Myxosporea), with identification of Myxobolusxiaoganensis n. sp. isolated from the silver carp Hypophthalmichthys molitrix.

Several parasites infecting the Asian carp species have been broadly spread along with the global fish trade. However, the diversity of specific parasite groups and their pattern of parasitism remain insufficiently elucidated even in their native regions. Here, we conducted a holistic identification and histological analysis of three Myxobolus species. The oblate myxospores of the first isolates were found infecting the spleen of silver carp Hypophthalmichthys molitrix, measuring 6.4 ± 0.4 (5.4-7.1) µm in length, 8.2 ± 0.4 (7.5-9.0) in width, and 5.9 ± 0.3 (5.2-6.2) in thickness. They were morphologically distinct from other congeners and regarded as a novel species, Myxobolus xiaoganensis n. sp. For the second isolates, we associated the formation of round plasmodia on the gill raker of silver carp with Myxobolus allotypica Chen, 1998. The third isolates, encapsulated in the intestinal serosa membrane of the grass carp Ctenopharyngodon idella, was proved to be conspecific to Myxobolus huasaensis Chen, 1998. While M. xiaoganensis n. sp. and M. huasaensis exhibited distinct origins, with genetic differences exceeding 4% from other congeners, M. allotypica displayed complete genetic congruence with an item available in Genbank. Histologically, myxospores of M. xiaoganensis n. sp. were scattered in the spleen, and the branchial and intestinal infections of M. allotypica and M. huasaensis were determined, respectively. Phylogenetic analysis demonstrated a non-monophyletic origin of both the Thelohanellus and Myxobolus genera, with a remarkable association of host affinity with myxosporean clustering.

FIRST RECORD OF A PARASITE, DACTYLOGYRUS CF. SKRJABINI (MONOGENOIDEA: DACTYLOGYRIDAE), INFECTING INVASIVE SILVER CARP, HYPOPHTHALMICHTHYS MOLITRIX (VALENCIENNES, 1844) (CYPRINIFORMES: XENOCYPRIDIDAE) IN NORTH AMERICA.

The parasites infecting invasive carps in North America (all Cypriniformes: Xenocyprididae: grass carp, Ctenopharyngodon idella [Valenciennes, 1844]; silver carp, Hypophthalmichthys molitrix [Valenciennes, 1844]; bighead carp, Hypophthalmichthys nobilis [Richardson, 1845]; and black carp, Mylopharyngodon piceus [Richardson, 1846]) are little studied, and no parasite has been reported from silver carp there. We herein surveyed silver carp from Barkley Reservoir and Cheatham Reservoir (Cumberland River, Tennessee; June and December 2021) and the White River (Arkansas; May 2022) and collected numerous monogenoid specimens infecting the pores on the outer face of the gill raker plate. We heat-killed, formalin-fixed, and routinely stained some specimens for morphology and preserved others in 95% ethanol for DNA extraction and sequencing of the large subunit ribosomal DNA (28S). We identified our specimens as Dactylogyrus cf. skrjabini because they had a dorsal anchor deep root that is much longer than the superficial root, an approximately parallel penis and accessory piece, and a relatively large marginal hook pair V. No type specimen of Dactylogyrus skrjabiniAkhmerov, 1954 (type host and locality is silver carp, Amur River, Russia) is publicly available, but we borrowed several vouchers (NSMT-Pl 6393) that infected the gill rakers of silver carp captured in the Watarase River, Japan. The original description of D. skrjabini was highly stylized and diagrammatical, differing from the specimens we studied from North America and Japan by the dorsal anchor having a superficial root and shaft that comprise a strongly C-shaped hook (the superficial root curves toward the dorsal anchor point) (vs. superficial root straight, at ∼45° angle to deep root and directed away from the dorsal anchor point), a single, much reduced transverse bar that is narrow for its entire breadth (vs. dorsal and ventral transverse bars robust and broad, having an irregular outline), an accessory piece that lacks digitiform projections (vs. accessory piece with 4 digitiform projections), and an accessory piece that lacks a half cardioid-shaped process (vs. accessory piece having a half cardioid-shaped process). Our 28S sequences (generated from 4 specimens of D. cf. skrjabini: 2 from Tennessee [763 base pairs (bp)] and 2 from Arkansas [776 bp]) were identical to 1 ascribed to D. skrjabini from Japan. The present study is the first verifiable and credible report of a parasite from silver carp in North America and the first nucleotide information for a parasite from silver carp in North America.

Bacterial communities in co-cultured fish intestines and rice field soil irrigated with aquaculture wastewater.

In some regions, integrated rice-fish farms have been developed to balance the needs of aquaculture wastewater discharge and rice field irrigation. In this type of aqua-agriculture system, soil is irrigated with aquaculture wastewater, and intestinal bacteria in cultured fish species likely impact soil bacteria through irrigation. However, little is known about the relationship between soil bacteria and intestinal bacteria in some carp species commonly co-cultured in some Asian regions. Therefore, we co-cultured five carp species in aquaculture ponds and used the aquaculture wastewater to irrigate rice fields for over 5 years, and then compared carp intestinal bacterial communities with rice field soil bacterial communities. The results from analysis of similarity and SourceTracker analysis showed that a low similarity (R = 0.7908, P = 0.001) and contribution (an average of 9.9% of bacterial genera) of intestinal bacteria to soil bacterial communities although 77.5% of soil bacterial genera were shared by intestinal bacteria. Our results also indicated that intestinal bacteria in the numerically dominant fish species in the co-culture system do not necessarily impact soil bacteria more significantly than those of less abundant carp species, and that intestinal bacterial communities in one single fish species may impact certain soil bacterial phyla more significantly than others. Our results provide a better understanding of the impact of aquaculture wastewater on rice fields and will be helpful for the development of this type of aqua-agriculture system.

Silver Carp (Hypophthalmichthys molitrix) (Asian Silver Carp) Presence in Danube Delta and Romania-A Review with Data on Natural Reproduction.

The Danube River has a large hydrographical basin, being the second largest river in Europe. The main channel flows through seven European countries with many species of fish inhabiting it. In this review we focused on the invasive species silver carp (Hypophthalmichthys molitrix), which plays an important ecological and economic role in its original habitat, but since introduced in Europe's rivers, the species has posed a serious ecological risk under global warming. In this review paper, we gathered data regarding silver carp, such as when and how it entered the Danube Delta and the water temperature suitable for its growth and reproduction, mainly in the context of global warming, as well as the nature of nutrition and the ecological risk the species poses.

Asian Carp, an Alternative Material for Surimi Production: Progress and Future.

Asian carp is a general designation for grass carp, silver carp, bighead carp, and black carp. These fish species belong to the family Cyprinidae. In 2018, more than 18.5 million tons of Asian carp were produced globally. Asian carp can be used for producing surimi, a stabilized myofibrillar protein concentrate that can be made into a wide variety of products such as imitation crab sticks, fish balls, fish cakes, fish tofu, and fish sausage. Surimi is usually made from marine fish, but Asian carp have been widely used for surimi production in China. The quality of surimi is affected by various factors, including the processing methods and food additives, such as polysaccharides, protein, salt, and cryoprotectant. With an impending shortage of marine fish due to overfishing and depletion of fish stocks, Asian carp have a potential to serve as an alternative raw material for surimi products thanks to their high abundancy, less emissions of greenhouse gases from farming, desirable flesh color, and sufficient gel forming ability. The utilization of Asian carp in surimi production could also contribute to relieving the overflow of Asian carp in the United States.

Asian carp: A threat to American lakes, a feast on Chinese tables.

Asian carp, which are widely distributed in Asia and Europe, are nutritious and popular with consumers. In China, Asian carp is a tasty dish and has been consumed for thousands of years. However, they are considered aggressive invasive species that threaten rivers, lakes, and indigenous species in the United States. Asian carp have proliferated greatly in the water basin of the Mississippi River and its tributaries, and they have caused severe ecological problems over the past 20 years. In recent years, several state governments along the Mississippi River have implemented assistance programs to eliminate invasive Asian carp, but these did not alleviate the threat. We conducted a survey to understand consumers' attitudes toward Asian carp in the United States, and related reports were reviewed to explore the possibility of Asian carp as food fish on American tables. Emphasis is placed on the farming history, functional characteristics, consumption preferences, and successful utilization methods for Asian carp in China. In addition, suggestions and possible utilization methods were proposed to improve the negative impression of Asian carp in the United States. Further research is needed to take full advantage of this huge excellent source of food or health supplements. This review provides ideas and directions for the use of Asian carp in the United States. We believe that through effective cooperation between China and the United States, the negative aspects of Asian carp in the United States could be diminished, and a mutually beneficial situation could be achieved.

Can we manage fisheries with the inherent uncertainty from eDNA?

Environmental (e)DNA, as a general approach in aquatic systems, seeks to connect the presence of species' genetic material in the water and hence to infer the species' physical presence. However, fisheries managers face making decisions with risk and uncertainty when eDNA indicates a fish is present but traditional methods fail to capture the fish. In comparison with traditional methods such as nets, electrofishing and piscicides, eDNA approaches have more sources of underlying error that could give rise to false positives. This has resulted in some managers to question whether eDNA can be used to make management decisions because there is no fish in hand. As a relatively new approach, the methods and techniques have quickly evolved to improve confidence in eDNA. By evaluating an eDNA based research programmes through the pattern of the eDNA signal, assay design, experimental design, quality assurance and quality control checks, data analyses and concurrent search for fish using traditional gears, the evidence for fish presence can be evaluated to build confidence in the eDNA approach. The benefits for fisheries management from adopting an eDNA approach are numerous but include cost effectiveness, broader geographic coverage of habitat occupancy, early detection of invasive species, non-lethal stock assessments, exploration of previously inaccessible aquatic environments and discovery of new species hidden beneath the water's surface. At a time when global freshwater and marine fisheries are facing growing threats from over-harvest, pollution and climate change, we anticipate that growing confidence in eDNA will overcome the inherent uncertainty of not having a fish in hand and will empower the informed management actions necessary to protect and restore our fisheries.

Toxicity of Carbon Dioxide to Freshwater Fishes: Implications for Aquatic Invasive Species Management.

Carbon dioxide (CO2 ) has been approved by the US Environmental Protection Agency as a new aquatic pesticide to control invasive Asian carps and other aquatic nuisance species in the United States. However, limited CO2 toxicity data could make it challenging for resource managers to characterize the potential risk to nontarget species during CO2 applications. The present study quantified the toxicity of CO2 to 2 native riverine fishes, bluegill (Lepomis macrochirus) and fathead minnow (Pimephales promelas), using 12-h continuous flow-through CO2 exposure at 5, 15, and 25 °C water temperatures. Resulting survival indicated that bluegill (median lethal concentration [LC50] range 91-140 mg/L CO2 ) were more sensitive to CO2 than fathead minnow (LC50 range 235-306 mg/L CO2 ) across all water temperatures. Bluegill were also more sensitive to CO2 at 5 °C (LC50 91 mg/L CO2 , 95% CI 85-96 mg/L CO2 ) than at 25 °C (LC50 140 mg/L CO2 , 95% CI 135-146 mg/L CO2 ). Fathead minnow showed an opposite response and were less sensitive at 5 °C (LC50 306 mg/L CO2 , 95% CI 286-327 mg/L CO2 ) relative to 25 °C (LC50 235 mg/L CO2 , 95% CI 224-246 mg/L CO2 ). Our results show that CO2 toxicity can differ by species and water temperature. Data from the present study may inform decisions related to the use of CO2 as a control tool. Environ Toxicol Chem 2020;39:2247-2255. Published 2020. This article is a U.S. government work and is in the public domain in the USA.

Evaluating the potential role of bioactive chemicals on the distribution of invasive Asian carp upstream and downstream from river mile 278 in the Illinois waterway.

Two non-native carp species have invaded the Illinois Waterway and are a threat to Great Lakes ecosystems. Poor water quality in the upper Illinois Waterway may be a factor contributing to the stalling of the carp population front near river mile 278. In 2015, the U.S. Geological Survey collected 4 sets of water samples from two sites upstream and 4 sites downstream from river mile 278, and one tributary. Each sample was analyzed for up to 649 unique constituents of which 287 were detected including 96 pesticides, 62 pharmaceuticals, 39 wastewater indicator chemicals, 29 metals, 19 volatile organic compounds (VOCs), 6 disinfection by-products (DBPs), 5 hormones, and 5 carboxylic acids. Potential for bioactivity was estimated by comparing chemical concentrations to aquatic life or human health criteria and to in-vitro bioactivity screening results in the U.S Environmental Protection Agency ToxCast™ database. The resulting hazard quotients and exposure-activity ratios (EARs) are toxicity indexes that can be used to rank potential bioactivity of individual chemicals and chemical mixtures. This analysis indicates that several bioactive chemicals (BCs) including: carbendazim, 2,4-D, metolachlor, terbuthylazine, and acetochlor (pesticides); 1,4-dioxane (VOC); metformin, diphenhydramine, sulfamethoxazole, tramadol, fexofenadine, and the anti-depressants (pharmaceuticals); bisphenol A, 4-nonylphenol, galaxolide, 4-tert-octylphenol (wastewater indicator chemical); lead and boron (metals); and estrone (hormone) all occur in the upper Illinois Waterway at concentrations that produce elevated EARs values and may be adversely affecting carp reproduction and health. The clear differences in water quality upstream and downstream from river mile 278 with higher contaminant concentrations and potential bioactivity upstream could represent a barrier to carp range expansion.

Resolving the genetic paradox of invasions: Preadapted genomes and postintroduction hybridization of bigheaded carps in the Mississippi River Basin.

The genetic paradox of biological invasions is complex and multifaceted. In particular, the relative role of disparate propagule sources and genetic adaptation through postintroduction hybridization has remained largely unexplored. To add resolution to this paradox, we investigate the genetic architecture responsible for the invasion of two invasive Asian carp species, bighead carp (Hypophthalmichthys nobilis) and silver carp (H. molitrix) (bigheaded carps) that experience extensive hybridization in the Mississippi River Basin (MRB). We sequenced the genomes of bighead and silver carps (~1.08G bp and ~1.15G bp, respectively) and their hybrids collected from the MRB. We found moderate-to-high heterozygosity in bighead (0.0021) and silver (0.0036) carps, detected significantly higher dN/dS ratios of single-copy orthologous genes in bigheaded carps versus 10 other species of fish, and identified genes in both species potentially associated with environmental adaptation and other invasion-related traits. Additionally, we observed a high genomic similarity (96.3% in all syntenic blocks) between bighead and silver carps and over 90% embryonic viability in their experimentally induced hybrids. Our results suggest intrinsic genomic features of bigheaded carps, likely associated with life history traits that presumably evolved within their native ranges, might have facilitated their initial establishment of invasion, whereas ex-situ interspecific hybridization between the carps might have promoted their range expansion. This study reveals an alternative mechanism that could resolve one of the genetic paradoxes in biological invasions and provides invaluable genomic resources for applied research involving bigheaded carps.

Data on the characterization of phthalate-degrading bacteria from Asian carp microbiomes and riverine sediments.

Datasets presented here were employed in the main work "Characterization of phthalate-degrading-bacteria from Asian carp microbiomes and riverine sediments" (Kolb et al., 2019a). The carcinogenic compounds dimethyl phthalate (DMP), diethyl phthalate (DEP), and dibutyl phthalate (DBP) are ubiquitous in the environment due to widespread production and distribution which can be taken up by aquatic organisms. Asian carp species silver (Hypophthalmichthys molitrix) and bighead (Hypophthalmichthys nobilis) are exposed to phthalates by ingestion and absorption. This article presents data on the characterization of phthalate-degrading bacteria isolated from Asian carp microbiomes and riverine sediments by means of sample collection, enrichment, and isolation. Graphical data presents substrate utilization profiles of consortium SK-1 and Rhodococcus ruber derived from the gut microbiome of H. molitrix. Additionally, phthalate-degrading microbes were isolated from the gut and scale microbiomes of Asian carp where scanning electron microscopy images show the morphology from samples of final enrichment cultures and isolates. Consortium SK-1 was subjected to amplicon sequencing where community data shows the distribution of taxa while enriched with 500 mg L-1 DMP, DEP, and DBP combined. The data presented can provide insights to future research since other phthalate-degrading isolates and consortia can potentially be isolated from the microbiomes of aquatic organisms.

Refinement of eDNA as an early monitoring tool at the landscape-level: study design considerations.

Natural resource managers use data on the spatial range of species to guide management decisions. These data come from survey or monitoring efforts that use a wide variety of tools. Environmental DNA (eDNA) is a surveillance tool that uses genetic markers for detecting species and holds potential as a tool for large-scale monitoring programs. Two challenges of eDNA-based studies are uncertainties created by imperfect capture of eDNA in collection samples (e.g., water field samples) and imperfect detection of eDNA using molecular methods (e.g., quantitative PCR). Occurrence models can be used to address these challenges, thus we use an occurrence model to address two objectives: first, to determine how many samples were required to detect species using eDNA; second, to examine when and where to take samples. We collected water samples from three different habitat types in the Upper Mississippi River when both Bighead Carp and Silver Carp were known to be present based on telemetry detections. Each habitat type (backwater, tributary, and impoundment) was sampled during April, May, and November. Detections of eDNA for both species varied across sites and months, but were generally low, 0-19.3% of samples were positive for eDNA. Overall, we found that eDNA-based sampling holds promise to be a powerful monitoring tool for resource managers; however, limitations of eDNA-based sampling include different biological and ecological characteristics of target species such as seasonal habitat usage patterns as well as aspects of different physical environments that impact the implementation of these methods such as water temperature.

Protein and lipid growth rates regulate bioaccumulation of PCBs and Hg in Bighead Carp (Hypophthalmichthys nobilis) and Silver Carp (Hypophthalmichthys molitrix) from the Three Gorges Reservoir, China.

This study evaluated the effect of growth of different tissue compartments on the bioaccumulation of mercury (Hg) and polychlorinated biphenyls (PCBs) in Silver Carp (Hypophthalmichthys molitrix) and Bighead Carp (Hypophthalmichthys nobilis) from the Three Gorges Reservoir (TGR), China. A non-steady state bioenergetics/toxicokinetic model was developed to simulate PCB and Hg concentrations in these two species and compared with field data. Simulations using constant whole body growth rate and constant tissue to whole body weight ratios were contrasted against simulations adopting age specific whole body and tissue/age specific growth rates for their goodness of fit to field data. The simulations using age/tissue specific growth rates demonstrated better fit to field data for PCBs compared to the constant growth rate models (22% improved R2), while both models explained similar variation in Hg concentration data. Both species demonstrated higher growth rates of lipids (on a daily basis) relative to whole body and protein contributing to higher growth dilution of PCBs compared to Hg. Although stable isotope data indicated some degree of diet and/or habitat shift, simulations assuming a constant diet concentration explained between 36 and 40% of the variation in fish concentrations for both contaminants and fish species. This study demonstrates that differences in the bioaccumulation rate of PCBs and Hg by Asian carp can be partially explained by differences in the growth rates of key tissue storage compartments associated with each contaminant. These differences in chemical-specific growth dilution subsequently contribute to differences in chemical retention and bioaccumulation patterns of Hg and PCBs by fish.

Comparative study on the gut microbiotas of four economically important Asian carp species.

Gut microbiota of four economically important Asian carp species (silver carp, Hypophthalmichthys molitrix; bighead carp, Hypophthalmichthys nobilis; grass carp, Ctenopharyngodon idella; common carp, Cyprinus carpio) were compared using 16S rRNA gene pyrosequencing. Analysis of more than 590,000 quality-filtered sequences obtained from the foregut, midgut and hindgut of these four carp species revealed high microbial diversity among the samples. The foregut samples of grass carp exhibited more than 1,600 operational taxonomy units (OTUs) and the highest alpha-diversity index, followed by the silver carp foregut and midgut. Proteobacteria, Firmicutes, Bacteroidetes and Fusobacteria were the predominant phyla regardless of fish species or gut type. Pairwise (weighted) UniFrac distance-based permutational multivariate analysis of variance with fish species as a factor produced significant association (P<0.01). The gut microbiotas of all four carp species harbored saccharolytic or proteolytic microbes, likely in response to the differences in their feeding habits. In addition, extensive variations were also observed even within the same fish species. Our results indicate that the gut microbiotas of Asian carp depend on the exact species, even when the different species were cohabiting in the same environment. This study provides some new insights into developing commercial fish feeds and improving existing aquaculture strategies.

The potential impact of aquatic nuisance species on recreational fishing in the Great Lakes and Upper Mississippi and Ohio River Basins.

Concern over the potential transfer of aquatic nuisance species (ANS) between the Great Lakes basin and the Upper Mississippi River basin has motivated calls to re-establish hydrologic separation between the two basins. Accomplishing that goal would require significant expenditures to re-engineer waterways in the Chicago, IL area. These costs should be compared to the potential costs resulting from ANS transfer between the basin, a significant portion of which would be costs to recreational fisheries. In this study, a recreational behavior model is developed for sport anglers in an eight-state region. It models how angler behavior would change in response to potential changes in fishing quality resulting from ANS transfer. The model also calculates the potential loss in net economic value that anglers enjoy from the fishery. The model is estimated based on data on trips taken by anglers (travel cost data) and on angler statements about how they would respond to changes in fishing quality (contingent behavior data). The model shows that the benefit to recreational anglers from re-establishing hydrologic separation exceeds the costs only if the anticipated impacts of ANS transfer on sport fish catch rates are large and widespread.

Crafting socialist embryology: dialectics, aquaculture and the diverging discipline in Maoist China, 1950-1965.

In the 1950s, embryology in socialist China underwent a series of changes that adjusted the disciplinary apparatus to suit socialism and the national goal of self-reliance. As the Communist state called on scientists to learn from the Soviets, embryologists' comprehensive view on heredity, which did not contradict Trofim Lysenko (1898-1976)'s doctrines, provided a space for them to advance their discipline. Leading scientists, often trained abroad in the tradition of experimental embryology, rode on the tides of Maoist ideology and repositioned their research. Some of their creative realignment of previous research questions, materials, and traditions to Marxist philosophy and agricultural objectives generated productive programs. In particular, Tong Dizhou (1902-1979) translated Engels's dialectics of nature into a research question about cytoplasmic inheritance. His continuing investigation on it led to the first goldfish "clone" through a nuclear transplantation experiment; Zhu Xi and his associates transferred a goldfish model in embryology into studies on improving carp aquaculture, leading to a rare success in the Great Leap Forward of 1958. These directions for embryology continued well into the 1960s. At a time when global embryology was diversifying and began to be molecularized, eventually forming "developmental biology," socialist embryology took shape in China with a different set of epistemic and practical commitments. The history of its development challenges and enriches our understanding of the concrete process of change in one discipline under Mao, showing ways in which scientists creatively adapted state-sanctioned ideologies and visions to do productive work outside the framework of molecular biology during the Cold War.

Hydrology controls recruitment of two invasive cyprinids: bigheaded carp reproduction in a navigable large river.

In the Mississippi River Basin of North America, invasive bigheaded carp (silver carp Hypophthalmichthys molitrix and bighead carp H. nobilis, also referred to as Asian carp) have spread rapidly over the past several decades. In the Illinois River, an important tributary of the Upper Mississippi River, reproduction appears to be sporadic and frequently unsuccessful, yet bigheaded carp densities in this river are among the highest recorded on the continent. Understanding the causative factors behind erratic recruitment in this commercially-harvested invasive species is important for both limiting their spread and managing their harvest. We analyzed weekly catch records from 15 years of a standardized monitoring program to document the emergence of age-0 bigheaded carp in relation to environmental conditions. The appearance of age-0 fish was generally linked to hydrographic attributes, which probably serve as a cue for spawning. However, we found profound differences in the number of age-0 fish among years, which varied by as much as five orders of magnitude in successive years. The strong link between summer flooding and age-0 fish production we observed emphasizes the importance of understanding the hydrologic context in which sustained invasions occur. Despite evidence of sporadic recruitment, bigheaded carp populations in the Illinois River appear to be consistent or increasing because of particularly strong, episodic year classes.

Top-down effects of an invasive omnivore: detection in long-term monitoring of large-river reservoir chlorophyll-a.

Invasive species are capable of altering ecosystems through the consumption of basal resources. However, quantifying the effects of invasive species in large ecosystems is challenging. Measuring changes in basal resources (i.e., phytoplankton) at an ecosystem scale is an important and potentially translatable response vital to the understanding of how introduced species influence ecosystems. In this study, we analyzed patterns of early summer chlorophyll-a in a large-river reservoir in response to invasion of silver carp (Hypophthalmichthys molitrix). We used 25 years of ecological data from a 30-km reach of Kentucky Lake collected before and after silver carp establishment. We found significant decreases in chlorophyll-a within certain reservoir habitats since establishment of silver carp. Additionally, environmental and biological drivers of phytoplankton production showed no significant differences before and after invasion. These results suggest seasonal, and habitat-specific consumptive effects of invasive silver carp on an important basal food web resource. Further, our results convey the utility of long-term quantitative biological and physiochemical data in understanding ecosystem responses to elements of global change (i.e., species invasions). Importantly, the observed changes in the basal food web resource of Kentucky Lake may apply to other ecosystems facing invasion by silver carp (e.g., Laurentian Great Lakes). Our study offers insight into the mechanisms by which silver carp may influence ecosystems and furthers our understanding of invasive omnivores.

Invasive planktivores as mediators of organic matter exchanges within and across ecosystems.

Bighead carp (Hypophthalmichthys nobilis) are an invasive planktivore that can greatly deplete planktonic resources. Due to the inefficient conversion of food into fish tissue, large portions of consumed materials are egested and shunted to benthic habitats. We explored how bighead carp alter pools of organic matter between planktonic and benthic habitats, and across ecosystem boundaries. Here, we report evidence from a manipulative experiment demonstrating that bighead carp greatly reapportion pools of organic matter from planktonic to benthic habitats to such a degree that additional effects propagated across ecological boundaries into terrestrial ecosystems. Strong direct consumption by bighead carp reduced filamentous algae, biomass and production of zooplankton, and production of a native planktivorous fish within planktonic habitats. Reduced herbivory indirectly increased phytoplankton (chlorophyll a). Direct consumption of organic matter by bighead carp supported high carp production and concomitant losses of materials due to egestion. Perhaps in response to organic matter subsidies provided by fish egestion, ponds having bighead carp had higher standing crop biomass of Chironomidae larvae, as well as cross-boundary fluxes of their adult life stage. In contrast, we detected reduced cross-boundary fluxes of adult Chaoboridae midges in ponds having bighead carp. Consideration of bighead carp as mediators of organic matter exchanges provides a clearer framework for predicting the direct and extended impacts of these invasive planktivores in freshwater ecosystems. The perception of bighead carp must evolve beyond competitors for planktonic resources, to mediators and processors of nutrients and energy within and across ecosystems.