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Common mudpuppy

The common mudpuppy (Necturus maculosus) is a large, fully aquatic salamander in the family Proteidae, native to eastern North America and notable for its neotenic retention of external gills throughout adulthood. Adults typically measure 8 to 13 inches (20 to 33 cm) in length, though some reach up to 19 inches (48 cm), with a robust body that is grayish-brown or rusty-brown dorsally, pale gray ventrally, and marked by irregular dark spots or blotches. It features bushy, red, plume-like gills behind a broad, flat head equipped with small eyes, each with a dark stripe running through it; all limbs bear four toes, and the tail is laterally compressed with a low fin. This species inhabits permanent freshwater environments such as rivers, lakes, streams, and reservoirs, favoring deep pools with muddy, gravelly, or rocky bottoms where it can shelter under debris, logs, or during the day. Its range extends from southeastern (including , , and ) southward through the to , , and in the United States, though it is absent from some areas like parts of the Adirondacks and in . Nocturnal and active year-round, the common mudpuppy emerges at night to forage on a primarily consisting of , , worms, mollusks, small fish, and carrion, using its sluggish movements to ambush prey in low-oxygen waters where its gills provide an advantage. Reproduction occurs via after involving spermatophores, with mating typically in fall or winter and females laying clusters of 30 to 200 eggs in spring or summer, which they guard until hatching after 30 to 70 days of incubation. Larvae resemble adults upon hatching and grow slowly, reaching at 4 to 6 years; individuals can live over 30 years in the wild, contributing to their ecological role as mid-level predators and obligate hosts for the endangered salamander mussel (Simpsonaias ambigua), whose larvae develop on their gills. Although populations are generally stable across much of its according to IUCN and NatureServe assessments, the common mudpuppy faces localized threats from degradation, , lampricide applications in control, and climate-related changes, prompting calls for enhanced monitoring and protection in vulnerable regions like the . Harmless to humans despite occasional misconceptions about toxicity, it serves as an indicator for health due to its sensitivity to environmental contaminants.

Taxonomy and systematics

Classification

The common mudpuppy (Necturus maculosus Rafinesque, 1818) is classified in the family , order Urodela (synonym ), class Amphibia, phylum Chordata, and kingdom Animalia. The Necturus Rafinesque, 1818, encompasses eight extant species of fully aquatic, neotenic salamanders known collectively as mudpuppies and waterdogs, all endemic to except for the distantly related European olm () in the same family. N. maculosus is the largest member of its genus, with adults attaining total lengths of up to 48 cm, in contrast to smaller congeners such as the dwarf waterdog (N. punctatus , 1929; maximum 19 cm) and the Alabama waterdog (N. alabamensis Viosca, 1937; maximum 22 cm), some of which exhibit partial habitat overlap in southeastern river systems. Recent taxonomic revisions have recognized additional species, including N. moleri (Apalachicola waterdog) and N. mounti (Escambia waterdog), based on genetic and morphological evidence. The represent an ancient lineage of perennibranchiate (externally gilled) salamanders, with the family's fossil record extending to the (Santonian stage, approximately 86–83 million years ago), including early forms like Bishara backa from . The divergence between the transatlantic genera and is estimated at more than 70 million years ago, based on mitochondrial genome phylogenies calibrated with fossil constraints. Within , molecular and fossil-calibrated analyses indicate that the major extant clades arose during the , around 5 million years ago. Historically, N. maculosus was first described as Siren maculosus by Constantine S. Rafinesque in 1818, based on specimens from , with the generic name later restricted to a separate family of eel-like salamanders. Subsequent synonymy includes Necturus maculatus Rafinesque, 1819, and former subspecies designations like N. m. stictus , 1941; taxonomic revisions through the , incorporating morphological and molecular data, have stabilized its placement, with significant updates in the including the elevation of related taxa.

Subspecies

As of 2025, the common mudpuppy (N. maculosus) is not recognized as comprising any ; the former southern form, N. louisianensis (Red River mudpuppy or waterdog), has been elevated to full status based on phylogenetic analyses demonstrating distinctiveness and limited . Morphologically, N. maculosus typically exhibits a to rusty brown dorsal coloration with distinct black or blue-black spots, and a gray venter that may be spotted or unspotted. In contrast, N. louisianensis displays a lighter tan or yellowish brown dorsum with red or dark spots, often accompanied by a light-colored venter lacking spots. The distribution of N. maculosus spans the , northeastern , and extends southward west of the Appalachians to northern , , and parts of the basin, from southeastern to southern . N. louisianensis is primarily confined to the basin, including the drainage and adjacent areas from southeastern and southern southward to north-central , with extensions into the drainage in and . Taxonomic debates regarding N. louisianensis have been resolved in favor of full rank in recent assessments, such as the SSAR 9th edition (2025) and Chabarria et al. (2018), based on phylogenetic distinctiveness and diagnosability, though some evidence of historical hybridization and in contact zones persists. Hybridization evidence includes documented zones in the basin where morphological traits intermix, indicating potential between the forms.

Phylogeography

The of the common mudpuppy (N. maculosus) reflects postglacial recolonization patterns following the approximately 20,000 years ago, with populations expanding northward from southern refugia in the basin. () analyses of the cytochrome b gene reveal evidence of this expansion, including a single widespread common within major clusters accompanied by numerous low-frequency, closely related haplotypes—characteristic of founder-driven recolonization dynamics. Specifically, data support one or more Mississippian glacial refugia, from which a western lineage diversified and spread into the upper , while an eastern lineage radiated across drainages. These patterns pertain to N. maculosus sensu stricto, excluding the now-separate N. louisianensis. Genetic diversity in N. maculosus exhibits a latitudinal gradient, with higher haplotype diversity observed in southern populations compared to reduced levels in northern populations, attributable to serial founder effects during northward expansion. Phylogeographic studies from 2005 to 2020 using mtDNA have identified 24 distinct haplotypes across the range, revealing significant population structure and isolation-by-distance patterns. These analyses delineate major clades, including a western cluster associated with and drainages and an eastern cluster linked to regions, with a primary genetic divide aligned to the . Historical barriers to , such as ancient river systems and proglacial lakes, contributed to the divergence of eastern and western lineages, while contemporary fragmentation by dams further restricts dispersal and exacerbates isolation among river basins. For instance, genomic assessments in systems demonstrate significant genetic differentiation correlated with dam presence, limiting connectivity even within relatively contiguous habitats. These patterns have implications, as the identification of distinct lineages and basin-level population structure supports the delineation of evolutionarily significant units () for targeted management, particularly in northern regions vulnerable to ongoing declines.

Physical characteristics

Appearance

The common mudpuppy (Necturus maculosus) is a robust, fully with adults typically measuring 20 to 33 cm (8 to 13 inches) in total length, though maximum lengths of up to 48 cm (19 inches) have been recorded. Weights generally range from 200 to 300 g, though larger individuals may exceed this. is minimal, with no consistent differences in size between males and females reported in some studies. Its body is stocky and elongated, with a broad, flattened head, small eyes, and a laterally compressed that aids in . Each foot bears four toes, a distinctive feature among salamanders. The skin is smooth and moist, facilitating alongside the prominent bushy . Dorsal coloration ranges from grayish-brown to blue-black, often marked with scattered black spots or blotches that may merge into stripes. The are bushy and bright red, serving as the primary respiratory structures. The venter is pale gray, sometimes with faint spotting. A system along the body detects water vibrations and movements, enhancing sensory perception in murky aquatic environments. Age-related changes include a tendency for older individuals to darken, with spotting density increasing or spots coalescing, sometimes resulting in nearly uniform black surfaces.

Neoteny

The common mudpuppy (Necturus maculosus) displays obligate neoteny, a type of paedomorphosis in which larval features persist into hood without progression to . This includes the lifelong retention of , tail fins, and an exclusively aquatic lifestyle, precluding any transition to a terrestrial form. Unlike facultatively paedomorphic , N. maculosus achieves while maintaining these juvenile traits, a developmental strategy fixed across its life history. In terms of , the function as the primary mechanism for oxygen uptake in N. maculosus, with supplemental occurring through the skin and . These , which are bushy and feathery, adapt to environmental conditions; for instance, individuals in oxygen-poor waters develop more elaborate structures compared to those in well-oxygenated habitats. Although use is minimal and typically involves occasional surface access in low-oxygen scenarios, the -based system supports the species' permanent existence. This neotenic condition offers evolutionary advantages by enabling specialized adaptation to stable aquatic environments, such as lakes and rivers, where provides no benefit and could impose risks. The underlying genetic mechanism involves suppression of thyroid hormone responsiveness; while thyroid hormone receptors are functional and can induce partial transformations in isolated tissues, systemic dysregulation prevents . Obligate neoteny is universal among Necturus species within the family , contrasting sharply with metamorphic salamanders like Ambystoma species, which retain the capacity for hormone-driven under varying ecological pressures.

Distribution and habitat

Geographic range

The common mudpuppy (Necturus maculosus) occupies a broad range across eastern and central , extending from southeastern and southern southward to northern and , and westward to eastern , , and sporadically to . This distribution represents the largest of any fully aquatic species in the region, primarily west of the but with extensions into adjacent drainages. Key regions include the , the drainage, and the system, where populations are often associated with large rivers, lakes, and connected waterways. The species is absent from certain areas, particularly where suitable permanent water bodies are limited. The overall post-settlement range has remained relatively stable, though local extirpations have occurred in polluted urban rivers, such as noted declines in the prior to 1950 due to industrialization and degradation; as of 2023, assessments by COSEWIC and NatureServe indicate that the range remains relatively stable overall, with ongoing localized declines in some urban and polluted areas. Two subspecies are recognized: N. m. maculosus in the northern portions, including the , and N. m. louisianensis (Red River mudpuppy) in the southern drainage from north-central to southeastern . Distribution is patchy in the , where unsuitable habitats such as steep gradients or intermittent streams limit occurrence to isolated drainages like parts of the upper basin.

Habitat preferences

The common mudpuppy (Necturus maculosus) occupies permanent aquatic , encompassing both lotic systems such as rivers, streams, and creeks, and lentic systems including lakes, ponds, reservoirs, and lagoons. It favors medium- to large-sized water bodies with stable flow regimes, such as clean-flowing rocky streams and large, sometimes turbid rivers, while also utilizing man-made structures like reservoirs. In terms of and cover, the species selects areas with rocky, muddy, gravelly, or vegetated bottoms that provide ample , including piles, , talus, rock slabs, logs, undercut banks, tree roots, and . Individuals typically hide under these features during the day to avoid predators and risks, and females attach eggs to submerged rocks or logs for protection. Water quality is critical, with preferences for cool temperatures between and 25°C, well-oxygenated conditions, and low to facilitate and . The mudpuppy exhibits for hypoxic environments compared to other salamanders, developing larger gills in low-oxygen waters, but it remains sensitive to pollutants and excessive that impair oxygen uptake. It thrives in low-light, murky conditions but avoids highly degraded or temporary waters. Microhabitat selection varies by system and season; in streams and rivers, deeper pools with cover are preferred, while in lakes, nearshore shallows or depths up to 30 meters are used. Seasonal shifts occur, with individuals moving to shallower, warmer waters in spring and fall for increased activity, and retreating to deeper, cooler areas in summer and winter to maintain optimal conditions. These habitat preferences are supported by key adaptations, including , which enables a fully lifestyle in permanent waters without , and a well-developed system that detects vibrations and water movements for navigation in turbid, low-visibility environments.

Behavior and ecology

Diet and foraging

The common mudpuppy (Necturus maculosus) is a carnivorous whose consists primarily of aquatic invertebrates, including , (such as larvae, , and nymphs), and mollusks, with occasional predation on small and amphibians. Gut content analyses from multiple studies spanning the 1980s to the 2020s reveal regional and habitat-specific variations in composition; for instance, in an urban coastal wetland, macroinvertebrates dominated at 51% of samples, with comprising 3.2% by abundance and 5.7% by occurrence, alongside leeches, isopods, amphipods, and like round gobies and zebra mussels. In contrast, analyses from lakes showed accounting for 60% of prey items by number and crustaceans (including ) at 20% frequency of occurrence, while contributed 81% of volume. These findings highlight as a recurrent but not universally dominant component, often emphasized in earlier studies as a key food source across the species' range. As an , the common mudpuppy employs suction feeding to capture prey, rapidly expanding its buccal cavity to draw in organisms while stationed in concealed positions among rocks or . Foraging occurs primarily at night, guided by chemosensory detection via the nares and , as well as the system for sensing water movements and vibrations from nearby prey. This sensory reliance enables effective hunting in turbid, low-visibility aquatic environments without visual cues. Studies using confirm opportunistic scavenging behaviors, with empty stomachs noted in up to 21% of sampled individuals, suggesting intermittent feeding patterns. Dietary preferences exhibit ontogenetic shifts, with juveniles targeting smaller invertebrates like insect larvae and amphipods, while adults shift toward larger items such as crayfish and fish, as evidenced by significant differences in prey communities among size classes (p = 0.001). Seasonal variations further influence composition, with exclusive reliance on invertebrates during summer and fall, and incorporation of fish (up to 30% frequency) in winter and spring, potentially reflecting prey availability and metabolic demands. In aquatic food webs, the common mudpuppy serves as a mid-level predator of macroinvertebrates, helping regulate invertebrate populations, and acts as a bioindicator of water quality due to its sensitivity to pollutants like heavy metals and microplastics, which have been detected in gut contents across sites.

Reproduction

The common mudpuppy (Necturus maculosus) engages in and mating primarily during the fall and winter months, with peak activity from September through April, though timing varies by latitude and water temperature. Males in breeding condition exhibit swollen e and prominent backward-pointing papillae, and they deposit s—small packets of —onto the in shallow water. Females pick up these spermatophores with their , facilitating ; courtship involves males approaching and positioning females over the spermatophore, often in aggregations of both sexes. Females can store for several months, up to six or more, before oviposition. Eggs are laid in spring, typically from April to June, in nests excavated beneath rocks, logs, or other cover in shallow, protected sites. Each female produces a clutch of 20–100 eggs, though ranges up to 174 have been recorded; the eggs are cream to yellow, 5–6.5 in diameter, and attached singly or in a to the underside of the via thin stalks or disc-like expansions, forming a gelatinous cluster roughly 15–30 cm in diameter. s guard the eggs throughout the , which lasts 38–63 days depending on water temperature (9–18°C), defending the nest from predators and while occasionally nearby; this may extend to hatchlings for up to 6–8 weeks post-hatching. Hatchlings emerge at 21–25 mm total length after 1–2 months of development, retaining a for initial nourishment and immediately exhibiting the neotenic form with and aquatic lifestyle. Juveniles grow slowly, remaining in the nest vicinity before dispersing, and reach at 4–6 years of age, when they attain a snout-vent length of approximately 13–16 cm. The species exhibits low relative to other amphibians, with relatively few eggs per but substantial investment in nest site selection and guarding, contributing to a lifespan of up to 30 years or more, though averages are lower in the wild.

Activity and interactions

The common mudpuppy (Necturus maculosus) exhibits strictly nocturnal activity patterns, remaining hidden under rocks, logs, or other cover objects during the day to avoid detection. It becomes active primarily at night, particularly in clear where visibility is low, to and move about its . Seasonal activity shows peaks during warmer months from to , with notable increases in and capture rates in and summer corresponding to rising temperatures. For locomotion, the species is a slow crawler or , relying on its four limbs to walk along the in a bottom-walking manner, while short bursts of involve tucking the limbs against the body. It produces squeaky vocalizations resembling a dog's , which may serve a defensive role against threats. Predators of the common mudpuppy include large such as and , wading birds like , and mammals including raccoons that forage near water edges. These animals target mudpuppies during nocturnal activity or when they venture into shallower waters, with mudpuppies relying on concealment and skin sensory organs to detect approaching threats. High rates of occur in commercial and recreational fisheries, where mudpuppies are frequently captured in nets or on baited hooks and often discarded. Interspecific interactions involve competition with other species for shelter sites under rocks and logs, particularly in shared habitats where cover is limited. Larger individuals occasionally prey on smaller congeners or conspecifics, contributing to size-based dynamics within the . interactions include their use as in some regions, though this practice has declined, and popularity in the aquarium pet trade due to their fully nature and distinctive appearance. Accidental captures in nets and traps remain common, leading to unintended mortality if not released properly.

Conservation

Status and threats

The common mudpuppy (Necturus maculosus) is assessed as Least Concern on the , with the most recent evaluation in 2023 indicating a stable global population across its wide range, though regional declines have been noted in portions of its distribution. Globally, the species is considered secure by NatureServe (G5 ranking), reflecting its broad occurrence in freshwater systems of eastern , but localized vulnerabilities persist due to habitat-specific pressures. In , the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assessed the Manitoba population as Endangered and the /St. Lawrence population as Not at Risk in 2023. In the , mudpuppy populations have experienced notable declines, with some areas showing reductions linked to since the mid-20th century; for instance, fisheries assessments suggest steady decreases in abundance over recent decades, potentially up to moderate levels in affected watersheds. Local extirpations have occurred in heavily polluted or altered sites, such as parts of western , where intensive sampling efforts have yielded no detections despite historical presence. In urban-influenced rivers like those in the St. Clair-Detroit system, anecdotal and survey data indicate reduced sightings over the past 20–30 years, though small populations remain detectable. Major threats to the common mudpuppy include from sediments, agricultural runoff, industrial chemicals, and lampricides used in control, which can cause direct mortality and respiratory stress due to the species' and permeable skin. Habitat by dams disrupts migration and , leading to isolated subpopulations with reduced viability, while in gear contributes to incidental deaths, particularly during spawning seasons. exacerbates these issues by altering water temperatures and increasing extreme weather events, such as floods and storms, which have been associated with mass die-offs in the . The ' long , estimated at approximately 15 years, hinders recovery from disturbances, as reproductive maturity is delayed (7–10 years) and adults have a lifespan of at least 30 years, with the oldest recorded at 34 years, in . Global adult estimates are not precisely quantified due to the cryptic of the and challenges in habitats, but regional studies suggest abundances ranging from hundreds to thousands per suitable , with overall numbers likely in the millions across the range when accounting for stable core areas. Recent monitoring efforts from 2020 to 2025, including surveys and targeted trapping in the and Midwest streams, indicate stable populations in rural, less-modified habitats with intact riparian zones, but heightened vulnerability in urban or agriculturally impacted systems where detection rates are lower and declines continue. These surveys underscore the need for ongoing assessment to track trends amid ongoing anthropogenic pressures.

Protection and research

The common mudpuppy receives legal protections at the level , where it is classified as threatened in and , and as a species of special concern in and . The species is not listed under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (). However, its use in the bait trade is regulated through laws restricting the collection, sale, and transport of native amphibians, such as Indiana's requirements for permits and reporting. Conservation actions target habitat improvement and reduced human impacts. Efforts include riverbank restoration, such as invasive vegetation removal and native plantings with additions along the to enhance shelter and substrate stability. removals are implemented to restore connectivity and flow regimes, benefiting mudpuppy habitats indirectly through support for host-dependent species like the salamander . Fishing regulations promote live release of mudpuppies incidentally caught as during winter , with states like establishing public reporting protocols to track encounters and minimize harm. Water quality enhancements fall under the Water , where Sections 402 and 404 require permits for pollutant discharges and dredge-and-fill activities that could degrade essential aquatic environments. Research from 2015 to 2025 has advanced genetic understanding and population assessment. A U.S. Geological Survey phylogeographic study using identified distinct western and eastern lineages separated by the , highlighting postglacial recolonization patterns and informing preservation of evolutionary potential. Population monitoring integrates (eDNA) with trapping; eDNA detected mudpuppies in six Ohio streams in 2019, including historically occupied and novel sites, demonstrating its efficacy for rapid surveys. Along the , eDNA and trap data from 2014 to 2016 confirmed occupancy post-restoration, while 2021 studies in validated eDNA for non-native population tracking. Captive breeding trials have explored reproduction, with successes in controlled settings to assess viability for future translocations, though implementation remains limited. Management plans incorporate species status assessments and broader frameworks. The New York Department of Environmental Conservation's 2025 assessment proposes special concern designation, recommending standardized protocols for use, lampricide impacts, and trend monitoring. Mudpuppies are addressed in state wildlife action plans and integrated into conservation strategies, emphasizing coordinated threat mitigation and safeguards. Ongoing needs include long-term monitoring to evaluate climate-driven changes, such as warming waters affecting populations and metabolic rates. Public education initiatives stress the risks of releasing bait-captured mudpuppies into unsuitable habitats, which can spread or disrupt local genetics, alongside guidance for unharmed returns.