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Amphibious fish

Amphibious fish are species of fish that routinely spend extended periods out of water, either on land or above ground, as an integral part of their life history, distinguishing them from purely aquatic air-breathing fish that remain submerged while accessing air.^[1] This amphibious lifestyle has evolved independently at least 33 times across at least 33 fish families^[2] and up to 87 times in broader lineages,^[3] involving over 200 extant species distributed among over 30 families and 17 orders.^[4] Representing less than 1% of the over 37,000 known fish species (as of 2025),^[5] these fish have adapted to terrestrial challenges driven primarily by aquatic hypoxia, habitat drying, and opportunities for feeding, reproduction, and predator avoidance on land.^[1]^[6] Key adaptations enabling this dual lifestyle include air-breathing organs such as lungs, skin, or modified gills, which facilitate oxygen uptake in air, alongside phenotypic plasticity that allows reversible changes in traits like locomotion, hydration, and nitrogen excretion to cope with gravity, desiccation, and altered gas solubility.^[4] For instance, many amphibious fish exhibit enhanced terrestrial locomotion, such as using pectoral fins for "walking" or "jumping," and specialized behaviors like storing water in buccal cavities to prevent dehydration during emersion.^[1] Notable examples include mudskippers (Periophthalmus spp.), which actively forage and court mates on mudflats while spending up to 80% of their time out of water, relying on skin breathing and periodic returns to water for hydration; lungfish (Protopterus spp.), which can aestivate in mud burrows for months using lungs; and the mangrove rivulus (Kryptolebias marmoratus), which tolerates prolonged air exposure through skin-based gas exchange and high desiccation resistance.^[7]^[1] These adaptations not only highlight convergent evolution but also provide insights into the physiological transitions that facilitated the emergence of tetrapods from aquatic ancestors.^[4]

Definition and Physiology

Definition

Amphibious fish are osteichthyan fishes belonging to the classes Actinopterygii (ray-finned fishes) or Sarcopterygii (lobe-finned fishes) that routinely spend significant portions of their life cycle out of water, fully emerging onto land as a normal part of their behavior and surviving through specialized physiological adaptations.^[4] These species, spanning over 200 extant forms across 40 families and 17 orders, tolerate the physical and chemical challenges of terrestrial environments, such as increased gravity and risk of desiccation, which differ markedly from aquatic conditions.^[4] This distinguishes amphibious fish from fully aquatic species, which rely exclusively on gill-based respiration in water and would suffocate if emersed for prolonged periods without access to dissolved oxygen.^[3] Unlike amphibians in the class Amphibia, which are tetrapods that typically undergo metamorphosis from gilled larvae to limbed adults with moist, scaleless skin suited for cutaneous respiration, amphibious fish remain anatomically piscine throughout life, retaining features like scales, fins, and gills while developing supplementary air-breathing capabilities.^[4] The scope of amphibious fish includes both facultative forms, which emerge opportunistically (e.g., to evade aquatic hypoxia or predators), and obligate forms, which must periodically leave water (e.g., during habitat drying) to access atmospheric oxygen or fulfill other needs.^[3]

Respiratory Adaptations

Amphibious fish have evolved diverse respiratory adaptations to facilitate oxygen uptake from air, often supplementing or replacing aquatic gill-based respiration during periods of emersion. These adaptations include specialized air-breathing organs derived from structures like the swim bladder, gills, or buccal cavity, as well as enhanced cutaneous surfaces, allowing these fish to exploit hypoxic aquatic environments or temporarily venture onto land.^[8] One primary type of air-breathing involves vascularized swim bladders functioning as lungs, seen in primitive species such as lungfish (Dipnoi) and bichirs (Polypterus spp.). In African lungfish like Protopterus spp., the paired lungs are highly vascularized and enable efficient aerial gas exchange, with air breathing accounting for approximately 90% of oxygen uptake even in well-oxygenated water. Bichirs possess a dorsally positioned, lung-like swim bladder divided into alveolar compartments that supports bimodal respiration, allowing oxygen diffusion directly into the bloodstream. Other species, such as mudskippers (Periophthalmodon spp.), rely on modified gills and buccal cavities, where they trap air in vascularized opercular chambers to maintain gill functionality out of water. Cutaneous respiration through moist, vascularized skin is prominent in several amphibious taxa, including the mangrove rivulus (Kryptolebias marmoratus), where the skin contributes significantly to oxygen influx during emersion.^[8]^[9]^[10]^[11]^[12] Air breathing in amphibious fish can be obligate or facultative, depending on the species' reliance on atmospheric oxygen. Obligate air breathers, such as African lungfish (Protopterus spp.), must surface periodically to avoid drowning, as their reduced gills provide minimal aquatic oxygen uptake. In contrast, facultative breathers like the northern snakehead (Channa argus) primarily use gills in water but switch to aerial respiration when dissolved oxygen levels drop below critical thresholds. This dichotomy reflects ecological pressures, with obligate forms often inhabiting seasonally hypoxic habitats.^[13]^[9]^[14] Accessory structures further enhance aerial respiration by aiding air storage and moisture retention. The climbing perch (Anabas testudineus) features a labyrinth organ—a complex, vascularized structure of folded epithelial plates in the suprabranchial chamber—that stores air and facilitates prolonged emersion, up to several days if the skin remains moist. Snakeheads (Channa spp.) possess vascularized gill arches, particularly the first two, which form a suprabranchial organ that retains water around the gills during land exposure, preventing desiccation while enabling gas exchange. These structures are innervated and perfused to optimize oxygen delivery.^[15]^[14] Physiologically, gas exchange in air offers higher oxygen diffusion rates compared to water—due to air's greater oxygen capacitance and lower boundary layer resistance—but poses risks of dehydration and carbon dioxide buildup. In amphibious fish, aerial respiration offers greater efficiency than aquatic gill exchange under hypoxic conditions, though it requires adaptations like reduced gill surface area to minimize water loss and enhanced vascularization for perfusion. For instance, in lungfish, the buccal force pump mechanism drives air into the lungs, but CO2 excretion is less efficient in air, leading to hypercapnia tolerance. Cutaneous pathways, while supplementary, are limited by diffusion barriers and necessitate behavioral moisture maintenance to sustain oxygen gradients.^[16]^[8]^[12]

Locomotory Adaptations

Amphibious fish exhibit diverse locomotory adaptations that facilitate movement on land, primarily through modifications to their fins and body structure to counter the challenges of gravity and substrate friction. In species like mudskippers (Periophthalmus spp.), pectoral fins have evolved into robust, limb-like appendages capable of supporting body weight and enabling forward propulsion, with the lower fin rays elongated for enhanced stability during terrestrial travel.^[17] Similarly, lungfish utilize their pectoral and pelvic fins for walking-like gaits, where these structures lift the body off the substrate and generate alternating strides reminiscent of early tetrapod locomotion.^[18] In mudskippers such as the barred mudskipper (Periophthalmus argentilineatus), pectoral fins feature 13 webbed rays, with the lower eight rays notably longer and thicker to bear weight, while proximal segments remain unsegmented for rigidity. Pelvic fins, comprising five soft rays and a spine, form a hook-like dorsal structure and foot-like ventral processes, aiding in anchoring and pushing against uneven terrain. These fin adaptations support a crutching mode of locomotion, where the fish swings its body forward using synchronous or alternating fin thrusts, achieving speeds up to several body lengths per second on mudflats.^[19] Lungfish, including the African lungfish (Protopterus spp.), demonstrate fin-based walking through the functional subdivision of pectoral fins into propulsive elements, allowing the animal to pivot its trunk and advance by planting the head and fins sequentially. This results in trackways showing distinct impressions from fin impacts, highlighting the fins' role in weight-bearing and propulsion without reliance on the tail for primary movement.^[18] Elongate species like swamp eels (Synbranchus spp.) employ tail propulsion for terrestrial inching, relying on lateral undulations of the body and caudal fin to inch forward across substrates, a mode suited to their snake-like form lacking prominent paired fins. In contrast, blennies utilize bounding or leap-frog gaits, where the tail and body coil to launch the fish forward in short jumps, while catfishes often resort to side-to-side oscillations for slow, undulatory progress, though this is less efficient on firm ground.^[17] Skeletal reinforcements underpin these behaviors, including ossified pectoral girdles with elongated radial bones and condylar joints in mudskippers, which enhance load-bearing capacity and range of motion. Muscular enhancements, such as increased cross-sectional area in adductor and abductor muscles (e.g., physiological cross-sectional area of 0.3474 normalized to V_body^{0.67} for the pectoral adductor profundus in P. argentilineatus), provide the force needed for lifting and thrusting, with plasticity allowing further adaptation through fast-twitch fiber proliferation in species like the bichir (Polypterus senegalus).^[19]^[17] Terrestrial locomotion imposes higher energy costs than aquatic movement due to gravitational demands, often met through elevated metabolic rates and muscle efficiency improvements via exercise-like exposure. Many amphibious fish mitigate these costs by maintaining small body sizes, as smaller jumpers like blennies expend less energy per distance traveled compared to larger crutchers.^[17]^[20]

Evolutionary Aspects

Origins and Independent Evolutions

The phylogenetic history of amphibious fish traces back to the Devonian period, approximately 400 million years ago, when early sarcopterygian (lobe-finned) fishes began exhibiting traits suggestive of transitional aquatic-terrestrial lifestyles. Fossil evidence from this era includes Eusthenopteron, a tetrapodomorph fish from the Late Devonian (~375 million years ago), whose robust fin skeletons—featuring elements like a humerus, radius, and ulna—provided structural support for weight-bearing and movement in shallow, vegetated waters, marking it as a key precursor to tetrapod limb evolution.^[21] Modern sarcopterygians, such as lungfish (Dipnoi), represent living fossils that have retained these ancient characteristics, persisting with minimal morphological change since their origins in the Early Devonian as nektonic predators that adapted to near-shore environments.^[22] Amphibious traits in fish have arisen through convergent evolution across diverse osteichthyan lineages, with at least 33 independent origins documented in species from approximately 40 families and 17 orders, spanning both ray-finned (Actinopterygii) and lobe-finned (Sarcopterygii) clades.^[4] This repeated emergence is primarily driven by selective pressures from hypoxic aquatic environments and periodic water scarcity, such as in intertidal zones or drying habitats, where air-breathing and terrestrial mobility conferred survival advantages without necessitating full terrestriality. Recent studies as of 2025 have further illuminated this convergence, including adaptations in visual systems for intertidal foraging and enhanced emersion tolerance in annual killifishes.^[23]^[24] Among key lineages, the Dipnoi originated around 400 million years ago in the Early Devonian, evolving paired lungs alongside gills to facilitate aerial respiration during environmental fluctuations.^[22] In contrast, amphibious adaptations in ray-finned fishes appeared more recently; for instance, gobies of the Oxudercinae subfamily, including mudskippers, diverged and developed terrestriality during the early Miocene (~23 million years ago), enabling them to exploit mudflat niches through enhanced fin propulsion.^[25] At the genetic level, duplications and regulatory shifts in Hox gene clusters, particularly HoxA and HoxD, underpinned these fin-to-limb transitions by modulating proximo-distal patterning and distal mesenchymal cell fate, allowing for increased skeletal complexity in fins while halting progression to fully terrestrial appendages.^[26] In fishes like zebrafish, which underwent whole-genome duplications, paralogous Hox genes (e.g., hoxa13a and hoxa13b) express in overlapping domains to support fin ray elongation rather than autopod formation seen in tetrapods.^[26]

Phenotypic Plasticity

Phenotypic plasticity in amphibious fish refers to the capacity for reversible or developmental changes in morphology, physiology, and behavior in response to environmental cues, enabling enhanced tolerance to terrestrial conditions without requiring genetic mutations. These adjustments often involve tissue remodeling, altered gene expression, and neurohormonal signaling, allowing fish to adapt rapidly to fluctuating aquatic-terrestrial interfaces. For instance, such plasticity manifests as interlamellar cell mass (ILCM) formation in gills, which reduces surface area to prevent dehydration and collapse during air exposure, while maintaining functionality upon return to water.^[4]^[27] A prominent example is gill remodeling in the mangrove killifish Kryptolebias marmoratus, where air exposure induces proliferation of epithelial cells between gill lamellae, forming a protective ILCM that is fully reversible within days of re-immersion. Similarly, in the bichir Polypterus senegalus, developmental plasticity leads to strengthened pectoral fins and modified skeletal elements, such as an elevated cleithrum angle, when juveniles are reared on terrestrial substrates, improving locomotor performance on land. In low-oxygen conditions, some species exhibit increased vascularization of the swim bladder to enhance aerial gas exchange; for example, the reedfish Erpetoichthys calabaricus shows adaptive modifications in swim bladder tissue during prolonged emersion, supporting buoyancy and respiration. These morphological shifts are complemented by behavioral plasticity, such as enhanced jumping ability in air-acclimated K. marmoratus due to reduced lactate accumulation and expanded muscle cross-sectional area.^[27] Environmental triggers like hypoxia, desiccation, and temperature fluctuations initiate these changes by activating oxygen-sensing pathways, notably the hypoxia-inducible factor-1α (HIF-1α) cascade, which upregulates genes for angiogenesis, metabolic reprogramming, and ionoregulation. In fish exposed to low oxygen, HIF-1α stabilizes and translocates to the nucleus, promoting expression of target genes such as vascular endothelial growth factor (VEGF) for tissue vascularization and Rh glycoproteins for ammonia excretion across skin or gills. Temperature shifts can exacerbate hypoxia effects, prompting broader physiological adjustments, while desiccation cues induce mucous cell proliferation to retain moisture. These responses are rapid, often occurring within hours to weeks, and are mediated by conserved molecular mechanisms across amphibious taxa.^[28]^[4] Phenotypic plasticity serves as an evolutionary bridge, permitting initial forays onto land in over 200 amphibious species spanning multiple lineages, where flexible traits provide survival advantages before selection fixes them genetically through processes like genetic assimilation. In P. senegalus, land-reared individuals display skeletal changes akin to early tetrapod transitions, suggesting plasticity facilitated macroevolutionary shifts from aquatic ancestors. This mechanism allows exploitation of ephemeral habitats, such as tidal mudflats, without immediate evolutionary commitment, potentially accelerating adaptation in heterogeneous environments.^[4]

Classification and Examples

Lung-Breathing Amphibious Fish

Lung-breathing amphibious fish possess specialized internal organs derived from the swim bladder or analogous structures that enable aerial respiration, allowing them to supplement or replace gill-based oxygen uptake in hypoxic aquatic environments or during terrestrial excursions. These organs, often referred to as lungs or labyrinths, facilitate obligate or facultative air breathing in various lineages, with most species exhibiting bimodal respiration.^[29] The Dipnoi, or lungfishes, represent one of the most ancient groups, comprising six extant species distributed across Gondwanan continents: four African species in the genus Protopterus (e.g., Protopterus annectens), one South American species (Lepidosiren paradoxa), and the Australian lungfish (Neoceratodus forsteri).^[30] These fish feature paired lungs that serve dual roles in gas exchange and buoyancy regulation, with vascularized partitions enhancing oxygen diffusion efficiency.^[31] African lungfishes, in particular, are obligate air breathers that can tolerate elevated carbon dioxide levels in their blood due to specialized hemoglobin adaptations and reduced metabolic rates during stress.^[32] To survive seasonal droughts, species like Protopterus burrow into mud and secrete a mucus-based estivation cocoon, entering a dormant state that can last from months to several years while relying solely on lung breathing through a small air channel.^[32] This estivation minimizes water loss and urea accumulation, with the cocoon providing protection against desiccation and predation.^[33] In contrast, the Australian lungfish retains a more facultative breathing strategy with a single lung, reflecting its adaptation to more stable, oxygen-rich river habitats.^[29] The Polypteriformes, including bichirs such as Polypterus senegalus and the ropefish Erpetoichthys calabaricus, possess paired, dorsally asymmetric lungs connected via spiracles for aerial gulping, enabling bimodal respiration in low-oxygen swamps and floodplains of Africa.^[34] These primitive actinopterygians use their lungs obligatorily in hypoxic conditions, drowning if prevented from surfacing, and the lung structure supports developmental parallels to tetrapod lungs in vascularization and surfactant production.^[35] With around 18 species confined to African freshwater systems, bichirs exhibit robust terrestrial tolerance, crawling over land using pectoral fins while accessing air.^[34] Within the Anabantiformes, the labyrinth organ—a highly vascularized, sponge-like suprabranchial chamber—functions as a lung equivalent, allowing species like the climbing perch (Anabas testudineus) and snakeheads (family Channidae, e.g., Channa striata) to extract oxygen from air during overland migrations or in stagnant waters.^[36] Snakeheads, comprising over 50 species primarily in Asian and African rivers, are often obligate air breathers with the labyrinth enabling survival out of water for days; many have become invasive in North American waterways, such as the northern snakehead (Channa argus) in the Potomac River basin.^[37]^[38] The climbing perch, native to Southeast Asian wetlands, uses its labyrinth for extended aerial excursions, crawling up to 50 meters over land to reach new water bodies.^[36] These adaptations underscore the convergent evolution of lung-like organs for amphibious lifestyles across disparate fish lineages.

Non-Lung-Breathing Amphibious Fish

Non-lung-breathing amphibious fish access atmospheric oxygen primarily through gills, highly vascularized skin, or buccopharyngeal mechanisms, enabling terrestrial excursions without reliance on internal lungs. These strategies often involve maintaining moisture to prevent gill collapse and facilitate diffusion-based gas exchange, differing from the ventilatory demands of lung-based systems.^[39] A key group comprises mudskippers in the Gobiidae family, particularly genera Periophthalmus and Boleophthalmus, which dominate Indo-Pacific mangrove and mudflat habitats. These fish employ buccal force pumps to draw air over their gills and rely on cutaneous respiration, with skin contributing 60-70% of oxygen uptake during emersion. Over 30 mudskipper species exist, exhibiting behaviors like burrow maintenance in moist microhabitats to sustain hours-long terrestrial activity.^[40]^[41]^[39] The Blenniidae family includes the Pacific leaping blenny (Alticus arnoldorum), adapted for intertidal life through combined skin and gill respiration. This species leaps 2-3 meters onto rocky shores to escape predators, remaining emersed for extended periods by absorbing moisture from wave spray to support cutaneous gas exchange.^[42]^[43] Swamp eels of the Synbranchidae family, such as Synbranchus marmoratus, utilize buccopharyngeal pumping to ventilate gills with air and supplement via skin diffusion, compensating for their reduced branchial surface area. This allows survival during hypoxic aquatic conditions or brief land movements in tropical freshwater systems.^[44]^[45]^[8] In the Siluriformes order, air-breathing catfishes like Clarias species feature suprabranchial chambers with arborescent gill modifications and buccal force pumps for aerial ventilation. These adaptations support prolonged emersion in oxygen-poor waters, with Clarias widespread across tropical freshwater habitats in Africa, Asia, and the Americas.^[46]^[47]^[39] The four-eyed fish (Anableps anableps) demonstrates skin vascularization enhancing cutaneous respiration, aiding gas exchange during surface swimming and occasional emersions in brackish Neotropical environments.^[12]

Behaviors and Habitats

Terrestrial Behaviors

Amphibious fish exhibit a range of terrestrial behaviors that enable them to exploit land-based resources and interactions, including foraging, social displays, predator avoidance, and navigation. These activities are facilitated by their ability to move out of water for extended periods, often in intertidal or floodplain environments where water levels fluctuate.^[17] Feeding on land is a key terrestrial behavior for many amphibious species, allowing access to prey unavailable in aquatic habitats. Mudskippers (genus Periophthalmus), for instance, actively forage for insects, crustaceans, and small invertebrates on mudflats, relying on acute visual acuity to detect movement and dexterous pectoral fins to maneuver and capture prey. They employ a unique feeding mechanism involving a "hydrodynamic tongue" formed by expelling water from the buccal cavity to slurp up terrestrial items, adapting suction feeding from water to air.^[48]^[49] Similarly, northern snakeheads (Channa argus) use sinuous lateral undulations for overland movement during emersion in response to poor water conditions. Social interactions among amphibious fish often occur on land, where individuals establish territories and court mates. In mudskippers, males perform elaborate courtship displays, including tail wagging and burrow construction to attract females, with burrows serving as shelters and spawning sites in the intertidal zone. These displays involve elevated postures and fin movements to signal readiness. Climbing perch (Anabas testudineus) use opercular rotations and body undulations for terrestrial locomotion, aiding overland excursions.^[50]^[51] Predator evasion strategies on land emphasize rapid escape and concealment. Blennies such as the blackspotted rockskipper (Ennomacrodus striatus) leap between rocks to evade threats, using powerful tail flips for dynamic jumps that propel them onto exposed surfaces, reducing predation risk from aquatic hunters. African lungfish (Protopterus spp.) enter estivation during droughts, burrowing into mud and secreting a mucus cocoon to avoid desiccation and predators, remaining dormant for months or years until water returns.^[52]^[53]^[54] Sensory adaptations support these terrestrial activities by enhancing detection and orientation. Mudskippers possess enhanced olfaction for locating food and mates on land, complemented by aerial vision that corrects for refractive differences between air and water, allowing precise navigation. They often perch on elevated structures for vigilance, scanning for predators and opportunities with binocular vision.^[55]^[56]

Habitat Preferences

Amphibious fish primarily inhabit environments at the air-water interface, where they can transition between aquatic and terrestrial realms to exploit resources or evade stressors. These species favor shallow, vegetated waters and transient aquatic systems that periodically become inhospitable, such as those experiencing hypoxia or desiccation. Globally, over 200 species across more than 40 families have evolved to occupy such niches, with a concentration in tropical and subtropical regions.^[4] Key primary habitats include mangrove swamps and intertidal mudflats, particularly for mudskippers (family Oxudercinae), which endure high salinity fluctuations during tidal cycles in coastal Indo-Pacific areas. In contrast, lungfish such as the African Protopterus and South American Lepidosiren genera thrive in seasonal rivers, swamps, and temporary pools across drought-prone regions of Africa and South America, where water bodies dry up for months, prompting aestivation. Snakeheads (family Channidae) occupy freshwater rivers, ponds, and flooded areas in Asian and African tropics, often utilizing monsoon-driven inundations for dispersal.^[4]^[57]^[58] Microhabitats further support these transitions, such as burrow systems in mudflats constructed by mudskippers to retain moisture and oxygen during low tides. Lungfish form protective mud cocoons in drying sediments, while snakeheads seek refuge in vegetated floodplains and forest edges during monsoons. These refuges mitigate exposure to aerial conditions while allowing access to terrestrial foraging grounds.^[4]^[59] Abiotic factors shape these preferences, with amphibious fish exhibiting tolerance to low dissolved oxygen levels in stagnant waters, elevated temperatures with large seasonal variations (often exceeding 30°C in tropical habitats), and fluctuating humidity that demands moist refuges to prevent desiccation. They preferentially select shallow, oxygen-poor, and vegetated aquatic zones that facilitate easy emergence, linking directly to their capacity for land-water shifts.^[4]^[57]

Ecological Role and Conservation

Ecological Importance

Amphibious fish play significant trophic roles in ecosystems by acting as both predators and prey, thereby linking aquatic and terrestrial food webs. For instance, mudskippers (genus Periophthalmus) forage on land for small invertebrates, including fiddler crabs (Uca spp.), which constitute a major component of their diet and helps regulate invertebrate populations in intertidal zones.^[48] As prey, mudskippers are consumed by shorebirds such as herons and greenshanks, as well as reptiles like snakes, facilitating energy transfer from aquatic primary producers to terrestrial predators.^[60] This bidirectional flow bridges aquatic-terrestrial trophic chains, enhancing overall ecosystem connectivity in mangrove and mudflat habitats.^[61] These fish also contribute to nutrient cycling by transporting organic matter between aquatic and terrestrial environments through their movements and waste production. Mudskippers, for example, consume detritus and invertebrates on mudflats, processing them into feces that release nutrients back into the soil and water, supporting mangrove productivity and microbial activity.^[62] Their burrowing behavior aerates sediments, promoting decomposition and nutrient availability for rooted plants and benthic organisms. In seasonal wetlands, species like lungfish (Protopterus spp.) during estivation may indirectly enrich surrounding soils with metabolic byproducts, though direct quantification remains limited. Amphibious fish serve as biodiversity indicators due to their sensitivity to environmental changes, particularly in wetland health. Mudskippers accumulate heavy metals and respond to pollution levels, making them effective sentinels for assessing intertidal ecosystem integrity and water quality degradation.^[60] Their presence and abundance reflect habitat connectivity, potentially aiding gene flow across fragmented wetlands by traversing land barriers that isolate purely aquatic populations.^[63] This role underscores their value in monitoring broader biodiversity dynamics in dynamic coastal systems. Ecological interactions involving amphibious fish include both mutualistic associations and disruptive invasions. Mudskippers' burrows create microhabitats that benefit co-occurring burrowing invertebrates by improving sediment oxygenation, fostering symbiotic-like enhancements to local biodiversity.^[64] Conversely, invasive snakeheads (Channa argus) in U.S. waterways outcompete native species for resources, reducing populations of 17 fish species by 30-97% through predation and habitat dominance, thereby altering food webs and nutrient dynamics.^[65]^[66]

Conservation Status

Amphibious fish face significant threats from habitat destruction, particularly the ongoing loss of mangrove forests, which serve as critical intertidal habitats for species like mudskippers; global mangrove coverage has been declining at a net rate of approximately 0.04% per year during 2010-2020, according to recent assessments, driven by coastal development, aquaculture, and deforestation.^[67] Climate change exacerbates these pressures by intensifying droughts and altering water availability, leading to reduced wetland extents and increased physiological stress on air-breathing species in freshwater and estuarine systems, with at least 17% of threatened freshwater fish species impacted by decreasing water levels and rising temperatures as of 2023. Additionally, overfishing targets some amphibious species for food and aquarium trade, while invasive species such as the northern snakehead (Channa argus) in North America compete with and prey upon native fish, causing declines of 30-97% in 17 of 21 affected native species through resource competition and predation. Conservation statuses vary across amphibious fish taxa, with some lung-breathing species listed as Endangered on the IUCN Red List; for instance, the Australian lungfish (Neoceratodus forsteri) is classified as Endangered primarily due to habitat fragmentation from dam construction, which restricts migration to spawning grounds and destroys essential macrophyte beds. In contrast, many non-lung-breathing amphibious fish, such as several mudskipper species (e.g., Periophthalmus novemradiatus), are categorized as Data Deficient, reflecting insufficient data on population trends and distribution to assess extinction risks accurately. Efforts to protect amphibious fish include the establishment of protected wetland areas, such as Ramsar Convention sites, which safeguard over 4.6 million acres of critical habitats in the United States alone and support global conservation of intertidal and estuarine ecosystems vital for these species. Captive breeding programs have been implemented for rare lungfish, with facilities developing techniques to produce stock for restocking and reducing pressure on wild populations, as seen in initiatives for the Australian lungfish that supply aquarium trade sustainably. Research into phenotypic plasticity is also advancing resilience strategies, examining how environmental cues enable adaptive responses in amphibious fishes to enhance survival amid habitat changes. Despite these measures, key knowledge gaps persist in amphibious fish conservation, particularly for understudied tropical species like mudskippers, where population monitoring is limited by remote habitats and fluctuating environmental conditions. The impacts of pollution on air-breathing efficiency remain poorly understood, as contaminants reduce dissolved oxygen levels and impair respiratory transitions, potentially compounding hypoxia stress in polluted coastal waters. Furthermore, there is a need for updated phylogenies incorporating post-2020 genomic studies, such as analyses of aquaporin genes in amphibious actinopterygians, to better resolve evolutionary relationships and inform targeted protection for diverse lineages; recent 2023-2025 studies have begun addressing this through whole-genome sequencing of select air-breathing fish lineages.^[68]

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Apr 1, 2007 · These findings indicate that K. marmoratus remodel their gill structures in response to air exposure and that these changes are completely reversible.
[25]
The evolutionary and physiological significance of the Hif pathway in ...
Sep 17, 2021 · Here, we discuss the impact of the Hif pathway on the hypoxic response and the contribution to hypoxia tolerance, particularly in fishes of the ...
[26]
[PDF] Circulation and Respiration in Lungfishes (Dipnoi)
Many air-breathing fish carry out aerial respiration using a gas bladder connected via a pneumatic duct to the esophagus (Wilmer,. '34; Johansen, '70; Randall ...
[27]
Lungfishes - Explore the Taxonomic Tree | FWS.gov
Branches of Dipnoi ; Subtribe, 0 ; Genus, 3 ; Subgenus, 0 ; Species, 6.
[28]
Circulation and respiration in lungfishes (dipnoi) - Wiley Online Library
This paper reviews the cardiorespiratory morphology and physiology of the living lungfishes, in the special context of their highly effective use of both air ...
[29]
A single-cell atlas of West African lungfish respiratory system reveals ...
Sep 13, 2023 · While gas exchange via gills facilitates respiration in water, a lung or swim bladder allows air breathing in a subset of fish species.
[30]
The West African lungfish secretes a living cocoon during ...
Recovery time may be needed between induced aestivation ... African lungfish Protopterus aethiopicus during 46 days of aestivation in a mucus cocoon.
[31]
Spiracular air breathing in polypterid fishes and its implications for ...
Jan 23, 2014 · Polypterids respire bimodally (both aquatically and aerially); they breathe air using ventrally paired lungs with a glottal valve and a ...
[32]
Molecular developmental mechanism in polypterid fish provides ...
Jul 28, 2016 · Tetrapods use lungs for respiration, which deliver oxygen from the air into the body and remove carbon dioxide from the body. Lung development ...
[33]
Life in a bubble: the role of the labyrinth organ in determining ...
Sep 4, 2017 · All anabantoids have a pair of suprabranchial chambers that each house an air-breathing organ known as the labyrinth apparatus: a complex bony ...
[34]
Comparative mitochondrial genomics and phylogenetics for species ...
Mar 20, 2023 · The family Channidae, members of which are commonly known as snakehead fish, includes 53 Channa species and three Parachanna species.
[35]
California's Invaders: Snakehead
Of the 38 different species belonging to the Channidae family, only around 12 of them are considered invasive or potentially harmful. Snakeheads have a long, ...Missing: diversity | Show results with:diversity
[36]
Air‐breathing fishes - Lefevre - 2014 - Wiley Online Library
Mar 4, 2014 · Being the only group of animals that can breathe both air and water efficiently, air-breathing fishes are the intriguing result of opposing evolutionary forces.
[37]
[PDF] Physiological Ecology of the Mudskipper: A Synthesis - Prized Writing
The skin and gills provide tandem respiratory function in both water and air, but while in air the skin facilitates 60-70% of the respiration (gills just 40-30 ...
[38]
[PDF] Evolution of the Cardiorespiratory System in Air-Breathing Fishes
Sep 28, 2012 · The efferent branchial arteries of all four gill arches of N. forsteri unite to form the dorsal aorta and other major arteries of the head. In ...<|separator|>
[39]
Pacific Leaping Blenny: Study Sheds More Light on Life of Legless ...
Nov 29, 2013 · It remains on land all its adult life but has to stay moist to be able to breathe through its gills and skin.Missing: Chaenopsia | Show results with:Chaenopsia
[40]
The Pacific Leaping Blenny: A Fish that Prefers to be on Land
Dec 28, 2015 · Unlike other species of blenny, members of this species can breathe through their skin as well as through gills allowing them to do enough gas ...Missing: Chaenopsia | Show results with:Chaenopsia
[41]
The Transition to Air Breathing in Fishes: IV. Impact of Branchial ...
Most of the tropical swamp eels (Synbranchidae) also breathe air in this manner while in hypoxic water, during terrestrial excursions and when confined to ...
[42]
High blood oxygen affinity in the air-breathing swamp eel ...
The Asian swamp eel (Monopterus albus, Zuiew 1793) is a facultative air-breathing fish with reduced gills. Previous studies have shown that gas exchange ...
[43]
Functional morphology of the respiratory organs of the air-breathing ...
Anatomical, light and scanning electron microscopic studies on the air-breathing dendritic organ on the sharptooth catfish (Clarias gariepinus) ... species of ...
[44]
Morphometric and morphological study of the respiratory organs of ...
The respiratory organs of the African sharptooth catfish, Clarias gariepinus, were studied to broaden existing understanding of the adaptive stratagems that ...
[45]
Foraging ecology of the amphibious mudskipper Periophthalmus ...
Dec 7, 2021 · Foraging strategy of the mudskipper ... Terrestrial feeding in the mudskipper Periophthalmus (Pisces: Teleostei): a cineradiographic analysis.
[46]
A fish that uses its hydrodynamic tongue to feed on land - Journals
Apr 22, 2015 · The mudskipper's hyoid motion pattern during terrestrial feeding was different from the general pattern observed for aquatic feeding in fish.
[47]
Emersion and Terrestrial Locomotion of the Northern Snakehead ...
Unlike adults, northern snakehead fry use caudally-directed tail-flip jumps to locomote on land, like many killifishes (Cyprinodontiformes; Bressman et al. 2016 ...
[48]
Burrow behaviour, structure and utilization of the amphibious ...
Burrow behaviour, structure and utilization of the amphibious mudskipper Periophthalmus chrysospilos Bleeker, 1853 in the Mekong Delta ... Following courtship ...
[49]
(PDF) Burrow behaviour, structure and utilization of the amphibious ...
Oct 23, 2025 · Mudskipper is an intertidal fish that lives in daily immersion, transitioning between terrestrial eating and migration into water and emersion ...
[50]
Terrestrial locomotion characteristics of climbing perch (Anabas ...
The anatomy of extant climbing perch (Anabas testudineus), including its locomotor structures and air-breathing organ, the labyrinth structure (Tate et al., ...INTRODUCTION · MATERIALS AND METHODS · RESULTS · DISCUSSION
[51]
Navigating Nature's Terrain: Jumping Performance Robust to ... - NIH
Jan 29, 2025 · striatus)), an amphibious combtooth blenny from the Blenniidae family, relies on dynamic jumping as a primary escape mechanism to evade ...
[52]
Chapter 18 Estivation: Mechanisms and control of metabolic ...
When avoidance is not an option, the common survival strategy is to enter a period of estivation. This is achieved through (1) behavioral adjustments aimed ...
[53]
Aestivation in African Lungfishes: Physiology, Biochemistry and ...
The African lungfish, Protopterus annectens, can undergo aestivation during drought. ... estivation in the African lungfish Protopterus dolloi. Article. Mar 2010.
[54]
Mudskippers and Their Genetic Adaptations to an Amphibious ...
Feb 7, 2018 · Amphibious fish spend periods of time out of water, in or above the ground surface, as normal parts of their life histories [1] · By presenting ...Missing: definition | Show results with:definition
[55]
Vision & Mechanoreception - The mudskipper
Apr 30, 2013 · It is a cluster of mechanosensory cells with hair-like structures that protrude from the skin surface (cilia), and are surrounded by a gelatinous cupula.Missing: navigation perch vigilance
[56]
Lungfish - an overview | ScienceDirect Topics
The lungfishes (Sarcopterygii, Dipnoi) represent the earliest stages in the evolution of lung-breathing in tetrapod vertebrates, which gave rise to amphibians, ...
[57]
[PDF] Snakeheads (Pisces, Channidae)—A Biological Synopsis and Risk ...
Aug 18, 2002 · flooded paddy-fields enclosed by forest; large fish can be found in pools of dried streams in forests.” Temperature range: No specific ...
[58]
Burrow behaviour, structure and utilization of the amphibious ... - NIH
We report the burrowing behaviour of the amphibious mudskipper, Periophthalmus chysospilos, from estuarine and coastal sites within the Mekong Delta (Vietnam).
[59]
[PDF] Mudskipper: A biological indicator for environmental monitoring and ...
Oct 28, 2014 · Their very strong and well-muscled pectoral fins move down the body and allow them to swing, inhabiting them between the tides and the rear fin ...
[60]
The Amphibious Mudskipper: A Unique Model Bridging the Gap of ...
Mudskipper gobies can bridge the gap from aquatic to terrestrial habitats by their amphibious behavior, but the studies are yet emerging.
[61]
Sources partitioning in the diet of the mudskipper Periophthalmus ...
Moreover, mudskippers also play an integral role in nutrient cycling within the ecosystem. They consume detritus and other organic matter and subsequently ...Missing: controlling | Show results with:controlling
[62]
NITROGEN METABOLISM IN THE AFRICAN LUNGFISH ...
encounters aerial exposure occasionally during drought ... offer the advantages of avoidance of desiccation and predation, but P. ... Estivation in South American ...<|separator|>
[63]
(PDF) Fragmentation, connectivity and fish species persistence in ...
Apr 13, 2017 · Results: Habitat loss and fragmentation were associated with reduced gene flow and decreased genetic diversity. Mean allelic richness was ...
[64]
Burrow structure and utilization in the mudskipper ... - ZSL Publications
Dec 23, 2020 · The burrows used by mudskipper provide shelter, spawning sites, and access to feeding grounds for other mudskipper species.<|control11|><|separator|>
[65]
Study finds snakeheads are affecting native fish populations
Jan 17, 2020 · Snakeheads are driving down native fish populations by eating their prey, causing 17 of 21 native species to decline by 30-97%. They also drive ...
[66]
What are the potential effects of snakeheads to our waters?
A major concern is that snakeheads might out-compete (and eventually displace) important native or other established predatory fish that share the same habitat.