Phalacrocorax Auritus Research Articles

Use of Artificial Eggs Reduces Double-Crested Cormorant (Phalacrocorax auritus) Fledging

Double-crested Cormorant (Phalacrocorax auritus) populations have rapidly grown across the United States. In some locations cormorant populations have become a management concern due to real or perceived effects on local fish populations, altering island vegetation, and displacing other colonial waterbirds. In north-central Minnesota on Leech Lake cormorant populations have been reduced and managed by various removal and population reduction methods, which include fall nest material removal, lethal shooting, and limited harassment. These methods can be time intensive, costly, and can cause cormorants to disperse and renest. This study examines the use of artificial eggs as a new management method to reduce cormorant populations by limiting their fledging success. A portion of viable cormorant eggs from 68 nests were replaced and the nests monitored, and 32 nests were monitored as controls on an island nesting colony. Results demonstrate that cormorant fledging success is reduced by using artificial eggs. The average number of near fledge young per nest that received artificial eggs was 0.7 while control nests that did not receive artificial eggs had an average of 2.5 young per nest. Use of artificial eggs reduces cormorant fledging success and minimizes the chance of adults renesting elsewhere.

A rapid method of preparing complex organohalogen extracts from avian eggs: Applications to in vitro toxicogenomics screening

Double-crested cormorants are piscivorous birds that breed in variably contaminated colonies across the Laurentian Great Lakes of North America. Collection and preparation of environmentally relevant extracts from eggs that contain variable concentrations of organohalogen contaminants represents a minimally invasive approach to characterize potential effects of exposure using in vitro bioassays. In the present study, a rapid, efficient lipid freeze-filtration extraction method was used to prepare extracts from double-crested cormorant eggs collected from 5 breeding colonies that had variable organohalogen contaminant burdens. Extracts, solubilized in dimethyl sulfoxide, were administered to chicken embryonic hepatocytes (CEHs) to determine effects on cell viability, 7-ethoxyresorufin-O-deethylase (EROD) activity, and messenger RNA expression using a chicken ToxChip polymerase chain reaction (PCR) array. The EROD median effect concentration (EC50) values were lower for extracts with greater organohalogen contaminant burdens and thus permitted an initial ranking of colonies based on the efficacy of eliciting an aryl hydrocarbon receptor-mediated response. The ToxChip PCR array data provided a more exhaustive, pathway-based evaluation of extract effects; variability in the transcriptomic profiles was associated with organohalogen contaminant burdens. For example, extracts from Mud Island (Detroit River, MI, USA) had among the highest organohalogen contaminant burdens and elicited a greater biochemical (EROD EC50 = 0.005) and transcriptomic response (22/43 genes altered on the array) in CEHs compared with the least contaminated site, which was Mandarte Island (BC, Canada; EROD EC50 = 0.172; 8/43 genes altered). Avian eggs represent a useful biomonitoring tool for determining complex mixture effects, and the combination of a rapid extraction method, an in vitro bioassay, and targeted endpoint evaluation (biochemical and transcriptomic) shows great promise as an environmental effects monitoring approach. Environ Toxicol Chem 2019;38:811-819. © 2019 Crown in the right of Canada. Published by Wiley Periodicals Inc. on behalf of SETAC.

Pond sediments on nesting islands in eastern Lake Ontario provide insights into the population dynamics and impacts of waterbird colonies

Marked increases in ring-billed gulls and double-crested cormorants in the Laurentian Great Lakes during the last century have garnered attention over their ecological impacts, sparking debates about management strategies. However, monitoring data are generally sparse and of short duration for these colonies, hampering the ability to place recent changes within long-term context. Sediment records from ponds immediately surrounded by colonies on nesting islands can be used to track past bird populations, as they release wastes with geochemical signals that can be tracked using traditional paleolimnological methods, such as diatoms and stable isotopes of nitrogen (δ15N). Here, we provide new information about waterbird nesting histories on islands in eastern Lake Ontario that are of interest to wildlife managers. In all bird-impacted ponds, eutrophic diatom assemblages and elevated sediment chlorophyll-a coincided with high signatures of δ15N in the recent sediments, signifying bird influence. An absence of significant bird impacts in the oldest portion of one sediment core indicates that the current cormorant colony size (>2000 birds) is unprecedented over the ~150-year record. Diatoms and sediment chlorophyll-a also responded to even a small, short-duration cormorant nesting event on an actively managed reference island. Collating our findings with those from four previously studied sediment cores from nearby islands, we show that cormorants are unlikely to have occupied eastern Lake Ontario in their current numbers within the past ~150 years. However, ring-billed gulls have likely used several islands in the area for most of the 20th century (and perhaps earlier) until present.

Effects of Repeated Sublethal External Exposure to Deep Water Horizon Oil on the Avian Metabolome

We assessed adverse effects of external sublethal exposure of Deepwater Horizon, Mississippi Canyon 252 oil on plasma and liver metabolome profiles of the double-crested cormorant (Phalacrocorax auritus), a large (1.5 to 3.0 kg) diving waterbird common in the Gulf of Mexico. Metabolomics analysis of avian plasma showed significant negative effects on avian metabolic profiles, in some cases after only two external exposures (26 g cumulative) to oil. We observed significant (p < 0.05) changes in intermediate metabolites of energy metabolism and fatty acid and amino acid metabolic pathways in cormorants after repeated exposure to oil. Exposure to oil increased several metabolites (glycine, betaine, serine and methionine) that are essential to the one-carbon metabolism pathway. Lipid metabolism was affected, causing an increase in production of ketone bodies, suggesting lipids were used as an alternative energy source for energy production in oil exposed birds. In addition, metabolites associated with hepatic bile acid metabolism were affected by oil exposure which was correlated with changes observed in bile acids in exposed birds. These changes at the most basic level of phenotypic expression caused by sublethal exposure to oil can have effects that would be detrimental to reproduction, migration, and survival in avian species.

Indirect Negative Impacts of Double-crested Cormorant (Phalacrocorax auritus) Management on Co-nesting Caspian Terns (Hydroprogne caspia) in Northern Lake Michigan, USA

Hat Island, Lake Michigan, Michigan, USA, is an important historical breeding location for Caspian Terns (Hydroprogne caspia) and other co-nesting species, including Double-crested Cormorants (Phalacrocorax auritus). Although a bird sanctuary of the Michigan Islands National Wildlife Refuge, Double-crested Cormorant management (egg oiling and killing adults) was allowed on Hat Island in 2010; in 2011 and 2012, management actions were restricted to shooting Double-crested Cormorants from at least 500 m offshore. Because the Double-crested Cormorant colony was spread across much of Hat Island, in 2010, a small area of Double-crested Cormorant nests nearest the Caspian Tern colony was left undisturbed to minimize negative impacts on Caspian Terns. Yet, data indicate that management actions had indirect negative impacts on Caspian Terns. Game camera images show that Caspian Terns experienced more frequent disturbances in 2010 as compared to 2011 and 2012. Furthermore, nest inventories and chick banding, in combination with direct chick re-sighting and camera images, show Caspian Tern reproductive success was lower and the colony was abandoned earlier in 2010, as compared to other years. This illustrates that Double-crested Cormorant control actions can cause unintended consequences to co-nesters, even when those conducting management report no impact, and exemplifies that there should be greater consideration of the impacts on co-nesters prior to management.

Nest site taphonomy of colonial ground-nesting birds at Bowdoin National Wildlife Refuge, Montana

ABSTRACT Nesting localities of extant birds and reptiles may provide taphonomic models for interpreting nesting sites of ancient archosaurs. Here we describe assemblages of nesting gulls (Larus delawarensis and L. californicus), American white pelicans (Pelecanus erythrorhynchos), and double-crested cormorants (Phalacrocorax auritus). Seventy nests yielded 2752 skeletal elements and 2308 eggshells. Most material was located inside the nest for gulls and consisted of osteologically mature gull bones and pelican eggshell. Pelican and cormorant nesting material were located outside the nest, with higher percentages of juvenile avian bone. Eggshell concave up and down ratios on the surface of gull nests compared closely to predated assemblages. Pelican and cormorant surface ratios were approximately 50:50, suggesting trampling by altricial young. Weathered bones in the subsurface of cormorant and pelican nests and layers of predated eggshell in gull nests suggest multi-year accumulations. The amount of material associated with the nests and the age of the nester’s bones provides a means of distinguishing altricial and semi-precocial nesting sites. Nesting grounds for gulls with semi-precocial young yielded less skeletal material but a higher proportion of mature gull bones, whereas the large assemblages with altricial pelican and cormorant nests were dominated by prey items and their own young.

Prioritization of 10 organic flame retardants using an avian hepatocyte toxicogenomic assay.

As the number of chemicals developed and used by industry increases, the inherent limitations of traditional toxicology approaches become an unavoidable issue. To help meet the demand for toxicity evaluation, new methods, such as high-throughput toxicity screening, are currently being developed to permit rapid determination of toxic, molecular, and/or biochemical effects of a wide range of chemicals. In the present study, we demonstrate the utility of an avian in vitro toxicogenomics screening approach to determine the cytotoxic and transcriptomic effects of 10 organic flame retardants (OFRs) currently of international priority for ecological risk evaluation to prioritize and inform future toxicological studies. Hepatocytes from 2 avian species, chicken and double-crested cormorant, were prepared and exposed for 24 h to various concentrations (0-300 μM) of the following 10 OFRs: Chemical Abstracts Service registration numbers 29761-21-5, 56803-37-3 (p-tert-butylphenyl diphenyl phosphate [BPDP]), 65652-41-7, 68937-41-7 (phenol, isopropylated, phosphate [3:1] [IPPP]), 95906-11-9, 19186-97-1, 26040-51-7, 35948-25-5, 21850-44-2, and 25713-60-4. Cell viability, the 7-ethoxyresorufin-O-deethylase assay, and transcriptomic analysis using species-specific ToxChip polymerase chain reaction arrays were performed to evaluate the in vitro effect of these OFRs. Of the 10 OFRs assessed, BPDP and IPPP elicited the strongest cytotoxic and transcriptomic responses in both chicken and double-crested cormorant hepatocytes and are therefore recommended as priority candidates for further wildlife toxicological investigations. Environ Toxicol Chem 2018;37:3134-3144. © 2018 Crown in the right of Canada. Published by Wiley Periodicals Inc. on behalf of SETAC.

West Nile Virus Prevalence in Wild Birds from Mexico.

West Nile virus (WNV) emerged in the Americas with its introduction in 1999 and now is considered endemic across the continent. In 2002, WNV was detected in Mexico, where its occurrence and mortality are considerably lower compared with the US. However, continuous national surveillance programs in Mexico are nonexistent. Birds are considered the primary hosts and primary geographic dispersers of this pathogen. A total of 200 cloacal and tracheal samples from wild migratory or resident birds were retrospectively analyzed using reverse transcription PCR to detect WNV from birds collected in Mexico from 2008 to 2009. The overall prevalence was 8% (16/200), and positive samples were from Oaxaca, Chiapas, and Tamaulipas in Ruby-throated Hummingbird ( Archilochus colubris), Double-crested Cormorant ( Phalacrocorax auritus), Ring-billed Gull ( Larus delawarensis), and Mourning Dove ( Zenaida macroura). Analysis of the partial sequence of the envelope gene from one of the samples from Oaxaca provided evidence that the virus belonged to the WN99 genotype. Taken together, these results demonstrated that WNV circulated in wild birds from northern and southern Mexico during the 2008-09 season, providing further information about the presence of WNV in Mexico.

Plumage Changes in Double-Crested Cormorants (Phalacrocorax auritus) within the Breeding Season: The Risks of Aging by Plumage

Scant attention has been given to the molting patterns of known-age Double-crested Cormorants (Phalacrocorax auritus). In general, subadult individuals are identified with a tan, buffy or mottled chest, and adults are identified with a black chest. While studying Double-crested Cormorant population dynamics in Ontario, Canada, with known-age birds, it was noted that the plumage of many (> 75%) breeding adults changed from black to heavily mottled during the course of the breeding season. No pattern with age was observed; plumage changed in equal proportions for all ages from 2-year-olds to 7-year-olds. A similar but reverse pattern has been observed with Double-crested Cormorants roosting at sites in the southeastern USA during fall migration. Whereas the majority of the roost had juvenile/subadult plumage in September, by mid-January the roost had shifted to 75% adult black plumage. The mechanism behind the plumage change is unknown, but extreme caution is advised when using plumage to age cormorants, especially during the winter months. By describing our observations with Double-crested Cormorants, we hope to encourage future formal research on within-season plumage changes.

Substituted diphenylamine antioxidants and benzotriazole UV stabilizers in blood plasma of fish, turtles, birds and dolphins from North America

Substituted diphenylamine antioxidants (SDPAs) and benzotriazole UV stabilizers (BZT-UVs) are additives used in industrial and commercial applications to prevent degradation by oxidation and are contaminants of emerging environmental concern. Little is known about the fate of these contaminants in wildlife, particularly in reptiles, birds and marine mammals. Nine SDPAs and six BZT-UVs were measured in blood plasma of seven fish species, snapping turtles (Chelydra serpentina), double-crested cormorants (Phalacrocorax auritus), and bottlenose dolphins (Tursiops truncatus) from various locations in North America. Plasma SDPAs were more frequently (90–100%) detected and with higher concentrations (median: 25–270 pg g−1, wet weight (ww)) in organisms from urban areas than rural locations (median: <method limits of quantification −136 pg g−1). The concentrations of most SDPAs generally followed the order of fish ≥ snapping turtles > double-crested cormorants > bottlenose dolphins. Of the three quantifiable BZT-UVs, 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (UV328) showed higher detection frequency in most species of fish, bird and turtle (range of 0–67%), indicating the widespread distribution of UV328 in the aquatic environment of lower Great Lakes region.

Experimental and modeled thermoregulatory costs of repeated sublethal oil exposure in the Double-crested Cormorant, Phalacrocorax auritus

To fully understand the impact of oil exposure, it is important to understand sublethal effects like how increased thermoregulatory costs may affect survival and reproduction. However, it is difficult and time-consuming to measure these effects in wild animals. We present a novel use of a bioenergetics model, Niche Mapper™, to estimate thermoregulatory impacts of oiling, using data from captive Double-crested Cormorants (Phalacrocorax auritus) experimentally exposed to oil. Oiled cormorants had significant increases in surface body temperatures following exposure. Niche Mapper accurately predicted surface temperatures and metabolic rates for unoiled and oiled cormorants and predicted 13–18% increased daily energetic demands due to increased thermoregulatory costs of oiling, consistent with increased food consumption observed in experimentally oiled cormorants. We show that Niche Mapper can provide valuable insight into sublethal oiling effects by quantifying the extent to which thermoregulatory costs divert energy resources away from important life processes like maintenance, reproduction and migration.

A Disconnect between Science and Management for Double-Crested Cormorants (Phalacrocorax auritus) in Northern Lake Michigan, USA, 2000–2016

In 2000, studies began on the Double-crested Cormorant (Phalacrocorax auritus) in the Beaver Archipelago, Lake Michigan, Michigan, USA, and have continued through the present. Research was conducted to determine whether Double-crested Cormorants were preying on smallmouth bass (Micropterus dolomieu) and causing a decline in this fishery. Breeding Double-crested Cormorant population estimates were recorded to document population dynamics before management and throughout the intensive control program, initiated in 2007. Research included studies using telemetry, raft surveys, banding, game cameras, and development of several bioenergetics models. In addition, co-nesting species were monitored to investigate impacts of Double-crested Cormorant control on non-target species. Results indicated that Double-crested Cormorants do not negatively impact smallmouth bass populations, co-nesters or other components of the system. However, control measures were initiated and continued through 2015; litigation ended control activities in 2016. Research suggested that control led to abandonment by Double-crested Cormorants of traditional colony sites, a switch from ground to tree nesting, and impacts on co-nesting species. This review demonstrates a significant disconnect between science-based knowledge and chosen management practices. Although court rulings ceased Double-crested Cormorant control, this disconnect should be addressed and remedied; science-based knowledge should be emphasized in any future management.

Living with Double-Crested Cormorants(Phalacrocorax auritus): A Spatial Approach for Non-Lethal Management in Toronto, Canada

Tree mortality incurred through the nesting habits of Double-crested Cormorants (Phalacrocorax auritus) can cause human-wildlife conflicts, often resulting in the lethal control of cormorants to reduce local population numbers in North America. In a protected area in Toronto, Ontario, Canada, that supports the largest colony of Double-crested Cormorants in North America, a non-lethal management approach to mitigate cormorant-induced tree mortality was adopted by the site managers in 2008. Double-crested Cormorants were managed for space occupancy rather than population size, with the main objective of minimizing tree mortality while supporting the cormorant population. Targeted non-lethal deterrence of tree-nesting Double-crested Cormorants was labor intensive, but effective in protecting trees. Between 2008 and 2016, the tree-nesting colony was prevented from expanding. Accessing ground-nesting Double-crested Cormorants only at night to avoid Larus sp. predation of Double-crested Cormorant nests appeared to be highly effective in minimizing disturbance; the ground-nesting colony expanded 899% over an 8-year period, with a 44% decrease in tree nesting. Ground-nesting Double-crested Cormorants had less impact on trees than tree-nesting individuals, and this spatially focused approach allowed for the sustained existence of a thriving colony.

Resolving Conflicts with Double-Crested Cormorants (Phalocrocorax auritus): The Importance of Knowledge-Based and Non-Traditional Approaches, an Introduction

This paper introduces the special section prepared for Waterbirds from selected papers originally presented at a symposium titled “Recent Advances in Biology and Management of Double-crested Cormorants (Phalocrocorax auritus)”, held in Bar Harbor, Maine, USA, at the 39th Annual Meeting of the Waterbird Society, 11–15 August 2015. The principal objective of this symposium was to explore and communicate about ways to address conflicts with this species that would result in fewer birds being killed under legal management programs. Fifteen papers were presented in three subject categories: population status and new research; knowledge-based challenges for Double-crested Cormorant management; and ethical, bird conservation and other perspectives on cormorant management. Three papers from the second two categories provided unique and important perspectives on ways to manage conflicts in which fewer birds would be destroyed and are presented here. The well-developed approaches in these papers are important steps toward a knowledge-based path to resolving conflicts and, most importantly, living with Double-crested Cormorants.

Ethical Foundations for the Lethal Management of Double-Crested Cormorants (Phalocrocorax auritus) in the Eastern United States: An Argument Analysis

Abstract. Lethal management of Double-crested Cormorants (Phalocrocorax auritus) has been implemented in many areas of the United States. In this paper, the philosophical method of argument analysis is used to assess ethical premises underlying the proposition that Double-crested Cormorant populations should be culled to reduce pressures on wild fisheries in the Great Lakes region of the eastern USA. This influential argument has been used to justify the destruction of more than half a million Double-crested Cormorants and hundreds of thousands of their nests and eggs. Three versions of the argument are formulated and assessed. It is shown that each of the arguments presupposes some form of anthropocentrism, an ethical stance considered by many in the scholarly community to be philosophically untenable and ethically inappropriate. It is suggested, consequently, that the arguments analyzed do not constitute an ethically sound basis for lethal management of Double-crested Cormorants in the Great Lakes regio...

Clinostomum poteae n. sp. (Digenea: Clinostomidae), in the trachea of a double-crested cormorant Phalacrocorax auritus Lesson, 1831 and molecular data linking the life-cycle stages of Clinostomum album Rosser, Alberson, Woodyard, Cunningham, Pote & Griffin, 2017 in Mississippi, USA.

Clinostomum spp. (Digenea: Clinostomidae) are a group of trematodes commonly found in the buccal cavity and oesophagus of a variety of piscivorous birds. The metacercariae, colloquially known as "yellow grubs," have been reported from a diverse group of freshwater fishes worldwide. In the catfish farming region of the southeastern USA, piscivorous birds present a continuous challenge for aquaculturists in the form of fish depredation and the introduction of trematodes into these static, earthen pond systems. Clinostomum spp. are commonly encountered in farm-raised catfish. While generally considered pests of minimal importance, heavy infections can result in unmarketable fillets. Of the piscivorous birds that frequent catfish aquaculture operations in the southeastern US, the double-crested cormorant (Phalacrocorax auritus Lesson) is one of the most damaging, although reports of Clinostomum spp. from P. auritus are limited. In this study, adult trematodes morphologically consistent with Clinostomum sp. were found in the trachea of a double-crested cormorant captured in Lowndes Co., Mississippi, USA. These specimens differed from other recognised Clinostomum spp. in several key morphological characters. Moreover, sequence data of mitochondrial cytochrome c oxidase subunit 1 gene (cox1), nicotinamide adenine dinucleotide dehydrogenase subunit 1 gene (nad1) and ribosomal internal transcribed spacer (ITS) regions did not match any known Clinostomum sp. for which sequence data are available. While genetically similar to C. marginatum and C. album Rosser, Alberson, Woodyard, Cunningham, Pote & Griffin, 2017 reported from the great egret Ardea alba L. in Mississippi, these adult clinostomids were larger in size and limited to the trachea, whereas both C. marginatum Rudolphi, 1819 and C. album are found in the oral cavity and esophagus. Given these distinct morphological and molecular characters we propose a new member of the genus, known hereafter as Clinostomum poteae n. sp. Additionally, larval stages in the life-cycle of C. album are morphologically and molecularly identified for the first time from ramshorn snails Planorbella trivolvis Say and fathead minnows Pimephales promelas Rafinesque.

Evidence for a Negative Effect of Double-crested Cormorants (&lt;i&gt;Phalacrocorax auritus&lt;/i&gt;) on Invasive European Fire Ants (&lt;i&gt;Myrmica rubra&lt;/i&gt;)

Nesting of Double-crested Cormorants (Phalacrocorax auritus) in western Lake Ontario is associated with reduced abundance and nest density of European Fire Ants (Myrmica rubra). The impact on fire ants may be substrate related. It is of potential importance because of the negative effect of fire ants on ground-nesting water birds.

Mercury Concentrations in Double-Crested Cormorant Chicks Across Canada.

Mercury (Hg) biomagnifies in aquatic food chains and can reach high concentrations in fish-eating birds. Spatial patterns of Hg have been found in freshwater ecosystems across Canada for many taxa, including fish and birds. However, it often is challenging to sample a representative population size of adult birds to monitor concentrations of contaminants over a large spatial scale. Moreover, adult birds can migrate and can show a contaminant profile that may not be representative of local resources. The goals of this study were (1) to determine if there was a spatial pattern of Hg concentrations in piscivorous birds, (2) to develop a model to estimate Hg concentrations in breeding adults using chicks as proxy, and (3) to develop predictive equations among non-lethal tissues that are representative of local resources in adults (blood and growing feathers). Double-crested Cormorant (Phalacrocorax auritus) chick growing feathers were sampled at 19 sites across Canada. Adult tissues (freshly grown feathers and blood) were sampled at five of those locations to establish correlations between age classes and between adult tissues. We found an increase in Hg concentrations with latitude up to 50°N followed by a decrease. There was a decrease in Hg concentrations from west to east, which contradicts previous studies. We found a good correlation of Hg concentrations between adults and chicks and among adult tissues. Our study shows that chicks are representative of adults and can be a suitable proxy for monitoring local mercury concentrations across Canada.

Sterols and stanols as novel tracers of waterbird population dynamics in freshwater ponds

With the expansion of urban centres in the mid-twentieth century and the post-1970 decrease in pesticides, populations of double-crested cormorants (Phalacrocorax auritus) and ring-billed gulls (Larus delawarensis) around Lake Ontario (Canada and USA) have rapidly rebounded, possibly to unprecedented numbers. Along with the use of traditional palaeolimnological methods (e.g. stable isotopes, biological proxies), we now have the capacity to develop specific markers for directly tracking the presence of waterbirds on nesting islands. Here, we apply the use of lipophilic sterols and stanols from both plant and animal-faecal origins as a reliable technique, independent of traditional isotopic methods, for pinpointing waterbird arrival and population growth over decadal timescales. Sterol and stanol concentrations measured in the guano samples of waterbird species were highly variable within a species and between the three species of waterbirds examined. However, cholesterol was the dominant sterol in guano, and phytosterols were also high in ring-billed gull guano. This variability highlights a specialist piscivorous diet for cormorants compared to a generalist, omnivorous diet for gulls, which may now often include grain and invertebrates from agricultural fields. A ratio that includes cholesterol and sitosterol plus their aerobically reduced products (cholestanol, stigmastanol) best explained the present range of bird abundance across the islands and was significantly correlated to sedimentary δ15N. Overall, we demonstrate the use of sterols and stanols as a direct means for tracking the spatial and temporal presence of waterbirds on islands across Lake Ontario, and probably elsewhere.

Potential of Double-crested Cormorants ( Phalacrocorax auritus), American White Pelicans ( Pelecanus erythrorhynchos), and Wood Storks ( Mycteria americana) to Transmit a Hypervirulent Strain of Aeromonas hydrophila between Channel Catfish Culture Ponds.

Aeromonas hydrophila is a Gram-negative bacterium ubiquitous to freshwater and brackish aquatic environments that can cause disease in fish, humans, reptiles, and birds. Recent severe outbreaks of disease in commercial channel catfish ( Ictalurus punctatus) aquaculture ponds have been associated with a hypervirulent Aeromonas hydrophila strain (VAH) that is genetically distinct from less virulent strains. The epidemiology of this disease has not been determined. Given that research has shown that Great Egrets ( Ardea alba) can shed viable hypervirulent A. hydrophila after consuming diseased fish, we hypothesized that Double-crested Cormorants ( Phalacrocorax auritus), American White Pelicans ( Pelecanus erythrorhynchos), and Wood Storks ( Mycteria americana) could also serve as a reservoir for VAH and spread the pathogen during predation of fish in uninfected catfish ponds. All three species, when fed VAH-infected catfish, shed viable VAH in their feces, demonstrating their potential to spread VAH.