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Oxudercidae
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| Oxudercidae Temporal range:
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|---|---|
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| Gobioides buchanani | |
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| Oxuderces dentatus | |
Scientific classification 
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Gobiiformes |
| Suborder: | Gobioidei |
| Family: | Oxudercidae Günther, 1861[1] |
| Synonyms | |
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Oxudercidae is a family of gobies which consists of four subfamilies which were formerly classified under the family Gobiidae. The family is sometimes called the Gobionellidae, but Oxudercidae has priority. The species in this family have a cosmopolitan distribution in temperate and tropical areas and are found in marine and freshwater environments, typically in inshore, euryhaline areas with silt and sand substrates.[2]
The Oxudercidae includes 86 genera, which contain around 600 species. This family has many species which occur in fresh water, and a number of species found on wet beaches and are able to live for a number of days out of water. The family includes the mudskippers, which include species that are able to move over land quite quickly. They have eyes located on the top of their heads on short stalks. They are capable of elevating or retracting them, and they can see well out of water. One species, Gillichthys mirabilis, usually stays in the water, but surfaces to gulp air when the oxygen levels in the water are low; it holds the air in its buccopharynx, which is highly vacularised to facilitate respiratory exchange.[2]
Fossil oxudercids are known from the Middle Miocene of Europe.[3]
Subfamilies
[edit]These subfamilies are included in the Oxudercidae:[2]
- Amblyopinae Günther, 1861[4]
- Gobionellinae Bleeker, 1874[5]
- Oxudercinae (including the mudskippers) Günther, 1861[6]
- Sicydiinae T.N. Gill, 1860[7]
References
[edit]- ^ Richard van der Laan; William N. Eschmeyer & Ronald Fricke (2014). "Family-group names of Recent fishes". Zootaxa. 3882 (2): 001–230.
- ^ a b c Nelson, JS; Grande, TC & Wilson, MVH (2016). Classification of fishes from Fishes of the World 5th Edition. Wiley. p. 330. ISBN 9781119220824.
- ^ Reichenbacher, Bettina; Bannikov, Alexander F. (2025-06-23). "Diversity of gobioid fishes in the late Middle Miocene of northern Moldova, Eastern Paratethys—part III: dwarf gobies". PalZ. 99 (3): 285–318. Bibcode:2025PalZ...99..285R. doi:10.1007/s12542-025-00726-z. ISSN 1867-6812.
- ^ Bailly N, ed. (2015). "Amblyopinae Günther, 1861". FishBase. World Register of Marine Species. Retrieved 29 July 2018.
- ^ Bailly N, ed. (2017). "Gobionellinae Bleeker, 1874". FishBase. World Register of Marine Species. Retrieved 29 July 2018.
- ^ Bailly N, ed. (2017). "Oxudercinae Günther, 1861". FishBase. World Register of Marine Species. Retrieved 29 July 2018.
- ^ Bailly N, ed. (2017). "Sicydiinae Gill, 1860". FishBase. World Register of Marine Species. Retrieved 29 July 2018.
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Oxudercidae
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Taxonomy
Classification and history
Oxudercidae belongs to the kingdom Animalia, phylum Chordata, class Actinopterygii, order Gobiiformes, and suborder Gobioidei.[4] The family was originally established by Albert Günther in 1861 to accommodate certain gobioid fishes with distinctive morphological features, such as the mudskippers.[2] Historically, Oxudercidae was treated as a junior synonym of the larger family Gobiidae following early 20th-century revisions that emphasized pelvic fin morphology and other traits to consolidate gobioids under a single family.[5] Subfamilies such as Oxudercinae, Amblyopinae, Gobionellinae, and Sicydiinae—previously nested within Gobiidae—encompassed taxa now assigned to Oxudercidae, including mudskippers and allied forms.[4] This classification persisted until molecular phylogenetic analyses in the late 2000s provided evidence for a deep divergence between these groups and Gobiidae, leading to the elevation of Oxudercidae to full family status in 2009 based on nuclear and mitochondrial DNA sequences that resolved it as the sister group to Gobiidae. Subsequent morphological corroboration and broader genomic studies in the 2010s, including revisions incorporating otolith and skeletal data, solidified this separation, with Gobionellidae recognized as a junior synonym of Oxudercidae.[4][2] Recent studies as of 2025 continue to affirm this familial status and subfamily arrangements, with ongoing descriptions of new species within these groups.[6] The family's temporal range extends from the Middle Miocene to the present, with the oldest unequivocal fossils, including dwarf gobies from northern Moldova, dating to approximately 11–13 million years ago and indicating early diversification in Indo-Pacific estuaries.[7]Etymology
The family name Oxudercidae is derived from the type genus Oxuderces, which combines the Greek "oxys" (ὀξύς), meaning sharp or pointed, and "derkḗs" (δερκής), alluding to sight or seeing, in reference to the prominent, protruding eyes of these fishes that feature movable membranous eyelids.[8] This etymology highlights the keen visual adaptations that allow members of the family, such as mudskippers, to survey their surroundings from above the substrate while partially buried.[8] The name Oxudercidae was formally established by the British zoologist Albert Günther in 1861 as a family-group taxon within the gobies, encompassing species with amphibious and mud-dwelling habits akin to mudskippers.[2] The subfamily Oxudercinae, also coined by Günther in the same work, shares this root, emphasizing the "sharp-sighted" quality linked to the elevated eyes that facilitate terrestrial vision in intertidal environments.[8][9] The standard taxonomic suffix "-idae" denotes a family in zoological nomenclature, while "-inae" indicates a subfamily.[8]Description
Morphology
Oxudercidae species are characterized by elongated, cylindrical bodies that are adapted for a primarily benthic lifestyle, with anterior portions rounded and posterior regions slightly compressed for maneuverability in confined spaces.[10] These bodies typically range from 5 to 30 cm in total length, though most species remain under 10 cm, reflecting their small size relative to other gobiiform fishes.[11] A notable exception is the genus Gobioides, where individuals can attain lengths exceeding 30 cm, up to 50 cm in standard length for some species.[12] The pelvic fins are fused medially to form a distinctive suction disc, consisting of a spine and five branched rays that enable firm attachment to substrates such as mud or rocks.[13] The head of Oxudercidae is proportionally large, featuring a terminal mouth suited for capturing small prey and cycloid scales that cover much of the body while being sparse or embedded on the head sides.[14] This scalation provides a smooth, flexible integument conducive to burrowing and movement through soft sediments. The dorsal fin configuration typically includes two separate fins: the first dorsal fin with 5-8 spines, and the second dorsal fin larger in size, bearing a single spine followed by 7-13 soft rays, which together enhance stability during locomotion.[15] Coloration across the family is generally mottled or camouflaged, often in shades of brown, green, or gray with irregular patterns that blend into muddy or vegetated substrates, facilitating concealment from predators in their varied habitats.[16] These patterns vary by species but emphasize cryptic adaptations over bright displays, with some individuals exhibiting subtle spotting or banding on the body and fins.[17]Adaptations to environment
Oxudercidae species exhibit diverse physiological and anatomical adaptations suited to their wide range of aquatic, brackish, and semi-terrestrial environments, including intertidal zones, mangroves, estuaries, and freshwater streams. These traits address challenges such as variable salinity, low oxygen levels, and dynamic substrates, enabling occupation of marginal habitats.[18] In the subfamily Oxudercinae (mudskippers), specialized eye structures feature protruding, dorsally positioned eyes that provide a wide field of view above the water surface, with a steeply curved cornea and flattened lens for acute aerial vision. These species employ a unique mechanism where the eyes retract into moist sockets protected by a vascularized dermal cup to prevent desiccation during emersion.[19][20][21] Respiratory modifications in amphibious Oxudercinae include highly vascularized skin and buccal cavity for cutaneous air breathing, with capillaries close to the skin surface (often within 2-7 μm) facilitating oxygen diffusion. The buccal epithelium supports gas exchange from air gulps, allowing emersion for up to several days while relying on burrow water for gills.[22][23][24] Muscular enhancements in the pectoral fins of Oxudercinae transform them into propulsive structures for terrestrial locomotion, with hypertrophied abductors and adductors anchored to elongated radial bones supporting crutching or skipping on land. Genetic changes in hox and tbx genes contribute to this fin strength.[25][26][18] Across the family, euryhaline physiology enables tolerance to salinities from near-freshwater (0 ppt) to hypersaline (up to 40 ppt), supported by osmoregulatory glands in gills and opercular membranes. Chloride cells extrude ions via Na+/K+-ATPase and CFTR channels, with low permeability and prolactin regulation minimizing stress during shifts.[27][28][29] In Amblyopinae, adaptations include robust burrowing behaviors with reinforced heads and bodies for constructing extensive underground networks in soft sediments, aiding survival in oxygen-poor mudflats. Sicydiinae species feature strong pelvic discs and pectoral fins for climbing steep, wet rocks and waterfalls in amphidromous life cycles.[30][3]Distribution and habitat
Geographic distribution
The family Oxudercidae exhibits a cosmopolitan distribution in tropical, subtropical, and temperate zones, primarily spanning the Indo-West Pacific region, where it achieves its highest diversity, as well as the eastern Atlantic, western Atlantic, and eastern Pacific coasts.[31][32] Species are notably absent from polar regions and deep oceanic waters, confining their presence to coastal and nearshore environments.[31] Key regions of abundance include Southeast Asian mangroves, particularly in the Indo-Malayan archipelago, where multiple species thrive in estuarine systems; African estuaries along the eastern Atlantic coast, supporting genera like Periophthalmus; and American coastal rivers in both the western Atlantic from the southern United States (New Jersey) to Brazil and the eastern Pacific from California, USA, to Peru.[31][32] Additionally, Indo-West Pacific freshwater systems host numerous species, especially from the subfamily Sicydiinae, which inhabit riverine and stream environments across tropical islands and continents.[31] Endemism is pronounced in isolated island chains, with high levels in Hawaii, where Sicydiinae species such as Lentipes concolor and Sicyopterus stimpsoni are endemic climbers restricted to native streams, and in Madagascar, featuring unique oxudercid radiations adapted to insular freshwater habitats.[33][31] Introduced species are rare but documented, with examples including species of the genus Rhinogobius established in non-native regions like the southern Caspian basin via aquarium releases and waterway transport.[34][35]Habitat types
Oxudercidae, commonly known as mudskippers and their allies, primarily inhabit intertidal zones characterized by soft substrates such as silt, sand, and mud. These environments include mudflats, mangrove forests, estuaries, and shallow coastal waters where tidal fluctuations expose and submerge the habitat regularly.[36][37] Species in this family thrive in these dynamic settings, often along tropical and subtropical coastlines, where the substrate supports burrowing and foraging activities.[16] Certain amphidromous species within Oxudercidae, such as those in the genera Stiphodon and Sicyopterus, undertake freshwater incursions into rivers and streams, including upstream migrations over waterfalls to access headwater habitats. These migrations enable larval development in marine environments followed by juvenile return to freshwater streams, supporting populations in clear, flowing waters with rocky or vegetated beds.[38][39] Microhabitat variations among Oxudercidae are pronounced, with many species burrowing into anaerobic mud to create moist refuges that maintain oxygen via trapped air pockets during high tides. During low tides, individuals often emerge to dwell on exposed mudflats or perches on mangrove roots and pneumatophores, facilitating terrestrial activities in these semi-aquatic niches.[37] Guilds differentiate by substrate openness, such as vegetated mangrove fringes for more arboreal species or open wet mud for burrowers near water edges.[37] Oxudercidae exhibit remarkable abiotic tolerances, being euryhaline with the ability to endure salinity fluctuations from near-freshwater levels (as low as 3 ppt) to hypersaline conditions (up to 50 ppt) influenced by tides, rainfall, and evaporation. They are also eurythermal, active across temperatures from 13°C to 40°C, and possess adaptations for low-oxygen environments, including hypoxia tolerance through aerial respiration in oxygen-poor mud and water.[36][37][40][41]Behavior
Locomotion and respiration
Members of the subfamily Oxudercinae (mudskippers) within the Oxudercidae family exhibit specialized locomotion adapted to their semi-terrestrial lifestyles in intertidal zones. In aquatic environments, they primarily rely on undulations of the caudal fin for propulsion and stability, supplemented by pectoral fin movements for maneuvering in shallow waters and precise positioning near the substrate.[42] This mode allows efficient navigation through mangrove channels and mudflats, where water depths are often limited, enabling quick transitions to land.[43] On land, Oxudercinae employ a quadrupedal "crutching" gait, utilizing robust pectoral and pelvic fins to support body weight and generate forward thrust, often in coordination with tail undulations for balance and acceleration.[43] This movement, characterized by synchronous fin lifts and vaults, facilitates slow, steady traversal over mud or sand, with escape responses involving "skipping" motions.[43] The pectoral fins, with elongated radials and reinforced skeletal elements like a wider cleithrum, provide the structural basis for weight-bearing and force transmission during these terrestrial activities.[42] In contrast, members of the subfamily Amblyopinae are primarily burrow-dwelling and remain aquatic, excavating extensive U-, Y-, or J-shaped burrows in soft mudflats for shelter and accessing air at burrow openings without emerging.[44] Gobionellinae species exhibit more typical benthic locomotion in estuarine habitats, relying on caudal fin propulsion and pelvic suction for substrate adherence in variable salinity environments. Sicydiinae gobies, adapted to freshwater streams, use specialized oral suckers for "inching" or climbing behaviors to ascend waterfalls and rapids during upstream migration.[45] Respiration in Oxudercidae shifts dramatically between aquatic and emersed states to support their amphibious habits, though this varies by subfamily. Underwater, they utilize gills for oxygen extraction, though gill surface areas are reduced in more terrestrial species (e.g., 76.3–315.0 mm²/g in Periophthalmodon), limiting prolonged submersion.[46] Out of water, Oxudercinae switch to aerial breathing via air gulping into a vascularized buccopharyngeal chamber, supplemented by cutaneous diffusion through highly vascularized skin that remains moistened by copious mucus secretions from epidermal mucous cells.[46][22] This dual mechanism allows species like Scartelaos histophorus to maintain an air phase in burrows and respire effectively during emersion.[47] Amblyopinae also perform air breathing from within burrows, gulping air at the surface while submerged in hypoxic water.[48] These adaptations enable Oxudercinae to sustain terrestrial activity for extended durations, often aligning with tidal cycles where low tides expose habitats for 12 hours or more; some species, such as obligatory air breathers in the genus Periophthalmodon, can remain active out of water for over 24 hours provided skin moisture is preserved.[46]Feeding habits
Members of the Oxudercidae family are primarily carnivorous or insectivorous, with diets consisting mainly of small invertebrates such as crustaceans (e.g., shrimp like Acetes spp. and crabs like Uca spp.), insects (e.g., ants like Dolichoderus sp.), polychaete worms, and mollusks, alongside incidental consumption of algae, detritus, and occasionally small fish.[49][50] Some species exhibit omnivorous tendencies, incorporating plant matter and microalgae, reflecting their adaptation to nutrient-rich intertidal environments.[51] Foraging strategies vary between aquatic and semi-terrestrial habitats and across subfamilies. In water, oxudercids typically use suction feeding facilitated by a highly protrusible mouth, which allows them to generate rapid inflow to capture bottom-dwelling prey efficiently.[43] On land, particularly among mudskipper genera like Periophthalmus and Periophthalmodon, individuals employ visual hunting, relying on elevated eyes to detect movement; they then lunge or skip toward prey, often flipping it into the air with pectoral fins or the mouth before ingestion.[51] Sicydiinae species, such as Sicyopterus, use their protrusible mouths for scraping algae and diatoms from rocks in fast-flowing streams, supplemented by invertebrate prey. These methods enable opportunistic exploitation of diverse prey in dynamic intertidal zones. Oxudercids serve as key mesopredators in estuarine and mangrove food webs, occupying intermediate trophic levels that connect primary consumers to higher predators, with their feeding contributing to nutrient cycling between terrestrial and aquatic systems.[50] Their active foraging lifestyles are supported by elevated metabolic rates, where active oxygen consumption can reach up to five times the standard rate, allowing sustained bursts of terrestrial activity.[52] Dietary habits undergo ontogenetic shifts, with planktonic juveniles primarily consuming zooplankton and microalgae during their larval phase, transitioning to benthic, invertebrate-dominated diets as adults settle in intertidal habitats.[50] This shift aligns with morphological changes, such as development of robust jaws for handling larger, solid prey.[53]Reproduction
Oxudercidae exhibit diverse reproductive strategies adapted to their intertidal and amphibious lifestyles, with many species displaying polygynous mating systems where males establish and defend territories to attract multiple females. In mudskipper genera such as Periophthalmus and Boleophthalmus, males perform elaborate courtship displays, including rapid "dancing" movements on land to signal readiness and territorial dominance, often synchronized with tidal cycles to maximize visibility during low tide. These displays involve tail flips, fin flares, and pushing behaviors to entice females toward the male's burrow, ensuring successful mate attraction in the exposed mudflat environment.[54] Spawning in Oxudercidae typically involves demersal eggs that are adhesive and laid on substrates within burrows or nests, with males providing extensive parental care through guarding and aeration. Females deposit eggs on the walls or ceiling of air-filled burrow chambers, where males fertilize them externally; in species like Periophthalmus modestus, males maintain oxygen levels by ferrying air into the chamber during low tide, preventing hypoxia in the enclosed space. Eggs are guarded by males for several days until hatching, which is often triggered by the male flooding the chamber during rising tides to submerge the eggs, achieving high hatch rates of around 80% under natural conditions. While most species rely on paternal nest guarding, mouthbrooding occurs in a few, such as certain Stiphodon taxa, where one parent incubates eggs orally to protect them from desiccation and predators. Breeding is seasonal, peaking during monsoon periods or high tides in tropical regions, which facilitate burrow access and larval dispersal.[54][55][56] Larval development varies across the family, reflecting habitat preferences from marine to freshwater systems. In estuarine and marine species like mudskippers (Periophthalmus spp.), eggs hatch into planktonic larvae that disperse in coastal waters for weeks before settling in intertidal zones, enhancing gene flow across populations. Amphidromous species, such as those in Sicyopterus and Stiphodon, produce larvae that drift downstream to the sea for a pelagic phase lasting 1-2 months, after which postlarvae migrate upstream to freshwater streams, using specialized mouth structures for climbing. This migration strategy ensures access to nutrient-rich upstream habitats while utilizing oceanic currents for dispersal. Fecundity ranges from 100 to 5,000 eggs per clutch in representative species, with larger females in Periophthalmus barbarus producing up to several thousand, allowing for multiple spawning events per season tied to environmental cues like rainfall and tidal amplitude.[38][57][56]Diversity
Subfamilies
The family Oxudercidae is divided into four subfamilies: Amblyopinae, Gobionellinae, Oxudercinae, and Sicydiinae, distinguished primarily by adaptations in fin morphology, eye position, and habitat specialization. These groupings reflect evolutionary divergences in lifestyle, from burrowing and subterranean existence to amphibious terrestrialism and stream-climbing behaviors.[58] Amblyopinae, comprising 15 genera and 38 species as of November 2025, consists of elongated, burrowing gobies often referred to as eel or worm gobies, adapted to low-light or dark environments such as subterranean waters, caves, and mudflats.[59] Members exhibit reduced or absent eyes, a hallmark eye position adaptation for their light-poor habitats, and a unique fin morphology with a 2:1 ratio of fin elements to vertebrae, along with continuous dorsal fins supported by single-ray pterygiophores. Their pink, purple, or red coloration in life aids camouflage in sediment, and they typically inhabit soft-bottom intertidal zones across the Indo-Pacific.[60] Gobionellinae, the largest subfamily with 76 genera and 542 species as of November 2025, includes euryhaline gobies primarily found in estuarine and freshwater habitats, though some like Gnatholepis occur in marine coral environments.[59] Distinguishing traits include variable fin morphologies suited to benthic lifestyles, such as fused pelvic fins forming a suction disc for substrate adhesion, and eyes positioned laterally for typical aquatic vision. This subfamily encompasses diverse forms, including the longjaw mudsuckers of the genus Awaous, which feature elongated jaws for feeding in silty waters, and emphasizes tolerance to wide salinity ranges across tropical and subtropical regions.[61] Oxudercinae, with 10 genera and 44 species as of November 2025, represents the fully amphibious mudskippers, specialized for intertidal life in mudflats and mangroves of the Indo-West Pacific.[59][15] Key distinctions include eyes positioned dorsally on the head for enhanced aerial vision, robust pectoral fins modified for quadrupedal "skipping" locomotion on land, and pelvic fins forming a strong adhesive disc.[62] Only four genera—Boleophthalmus, Periophthalmodon, Periophthalmus, and Scartelaos—are considered true mudskippers with advanced terrestrial adaptations, while others show intermediate aquatic-terrestrial traits.[63] Sicydiinae, encompassing 9 genera and 122 species as of November 2025, comprises amphidromous climbers adapted to fast-flowing freshwater streams and waterfalls in tropical islands and continents.[59] They are characterized by a specialized oral disc formed by highly fused and expanded pelvic fins for suction-clinging to rocks, enabling ascent of steep surfaces, and forward-positioned eyes for navigating turbulent waters. Habitat specialization drives their morphology, with robust bodies and modified mouths supporting larval marine dispersal followed by upstream migration.[64]Genera and species
The family Oxudercidae encompasses significant taxonomic diversity, comprising 110 valid genera and 746 valid species as recognized in Eschmeyer's Catalog of Fishes as of November 2025.[59] This substantial number reflects the family's radiation across diverse aquatic environments, particularly in tropical and subtropical regions. The genera vary widely in size, from monotypic lineages to those with dozens of species, contributing to the overall richness. Diversity within Oxudercidae is unevenly distributed across its four subfamilies, as outlined in updated phylogenetic frameworks. The subfamily Amblyopinae includes 15 genera and 38 species, many of which are specialized for subterranean or low-light habitats, such as caves and brackish aquifers.[59] Gobionellinae is the most speciose, with 76 genera and 542 species, encompassing a broad array of euryhaline forms adapted to estuarine and freshwater systems. Oxudercinae contains 10 genera and 44 species, primarily intertidal and amphibious taxa like mudskippers. Sicydiinae comprises 9 genera and 122 species, notable for its high proportion of amphidromous species that migrate between marine and freshwater realms during life cycles.[59]| Subfamily | Valid Genera | Valid Species | Key Characteristics |
|---|---|---|---|
| Amblyopinae | 15 | 38 | Specialized for low-light environments[59] |
| Gobionellinae | 76 | 542 | Diverse euryhaline and freshwater forms[59] |
| Oxudercinae | 10 | 44 | Intertidal and amphibious adaptations[59] |
| Sicydiinae | 9 | 122 | Many amphidromous life histories[59] |