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Monodactylidae
Monodactylidae
Monodactylidae
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Monodactylidae
Temporal range: Early Eocene to present
Silver moony, Monodactylus argenteus
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Acanthuriformes
Family: Monodactylidae
D. S. Jordan & Evermann, 1898
Genera

Monodactylidae is a family of acanthuriform bony fish commonly referred to as monos, moonyfishes or fingerfishes. All are strongly laterally compressed with disc-shaped bodies and tall anal and dorsal fins. Unusually for fish, scales occur on their dorsal fins and sometimes on the anal fins. The pelvic fins are small, sometimes vestigial. They are of moderate size, typically around 25 centimetres (9.8 in) in length, and Monodactylus sebae can be taller than it is long, measuring up to 30 centimetres (12 in) from the tip of the dorsal fin down to the tip of the anal fin. These long, scaly fins have given them the name "fingerfishes". Most are silvery with yellow and black markings; the juveniles are especially attractive, and most species are popular as aquarium fish.

Taxonomy

[edit]
Fossil specimen of Psettopsis

The family contains only a single extant genus, Monodactylus. They are distributed along the coastlines of Africa, India, and southern Asia, and as far west as Australia. Species of Monodactylus in particular commonly occur in estuaries. They are truly euryhaline and can live in fresh water for extended periods. Moonyfishes are predators and feed primarily on smaller fish and invertebrates. They are found primarily in shallow water and form large shoals. Two extinct genera, †Psettopsis Blot, 1969 and †Pasaichthys Blot, 1969, are known as fossils from the Early Eocene-aged lagerstatten of Monte Bolca, Eocene, in Italy.[1]

The genus Schuettea closely resembles members of Monodactylus, and was formerly also placed in the family. However, phylogenetic evidence suggests that the two belong to different orders, with Schuettea belonging to Acropomatiformes.[2][3]

In aquaria

[edit]
The species Monodactylus argenteus is a popular salt-water aquarium fish.

Aquarists commonly keep M. argenteus and M. sebae as pets in domestic aquaria, where they are known as monos or Malayan angels; they are also widely kept in public aquaria. They are hardy and easy to care for, but require brackish water and copious swimming space. [1].

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Monodactylidae

View on Grokipedia
from Grokipedia
Monodactylidae is a small family of ray-finned fishes in the order , commonly known as moonyfishes, fingerfishes, or monos, distinguished by their deep-bodied, strongly laterally compressed form that gives them a disc-like appearance, silvery scales, and symmetrical long-based dorsal and anal fins with the anterior soft rays elongated. These schooling species inhabit coastal marine, estuarine, and occasionally freshwater environments, primarily in the Indo-West Pacific and West African regions, where they frequent bays, areas, tidal creeks, and reefs at depths from shallow waters to about 30 meters, feeding on small , , and . The family comprises two recognized genera—Monodactylus (with four species: M. argenteus, M. sebae, M. kottelati, and M. falciformis) and Schuettea (with two species: S. scalaripinnis and S. woodwardi)—totaling six extant species, though some classifications debate the placement of Schuettea and suggest up to three genera and seven species overall. Notable for their adaptability to varying salinities, monodactylids are popular in the aquarium trade due to their striking appearance and peaceful behavior, with juveniles often displaying prominent pelvic fins that reduce or become vestigial in adults. Fossil records of the family date back to the lower Eocene, indicating an ancient lineage within percomorph fishes.

Taxonomy

Etymology

The name Monodactylidae derives from the Greek words monos (meaning "single" or "only") and daktylos (meaning "finger"), alluding to the characteristic single free ray in the pelvic fin of its members. This etymological root originates from the Monodactylus, established by in 1801. The family Monodactylidae was formally named and described by and Barton Warren Evermann in their 1898 work The Fishes of North and Middle America. Common names for the family, such as moonyfishes or fingerfishes, reflect the disc-like body shape and the distinctive fin structure that inspired the scientific nomenclature.

Classification

Monodactylidae is classified within the kingdom Animalia, phylum Chordata, class , order , and family Monodactylidae. This placement reflects a phylogenetic framework that integrates molecular sequence data from multiple loci with morphological traits, resolving the family as part of the diverse percomorph fishes. Historically, Monodactylidae was included in the large, polyphyletic order , a traditional grouping based primarily on shared morphological features like spiny dorsal fins. However, comprehensive phylogenetic analyses using genomic and multi-locus data since the early 2010s have demonstrated that is not monophyletic, leading to its disassembly and the reassignment of Monodactylidae to , a encompassing surgeonfishes and allies with robust support from both molecular and morphological evidence. The family's fossil record extends to the Early Eocene, approximately 50 million years ago, with the earliest known representatives consisting of extinct genera such as Psettopsis and Pasaichthys preserved in the exceptional of Monte Bolca, . These fossils, described from Ypresian-aged deposits, provide key insights into the early diversification of acanthuriform-like percomorphs. More recently, in 2024, a new Zaiaichthys with two (Z. postalensis and Z. watersi) was described from the same deposits, increasing the known Eocene diversity of the family. The Schuettea, previously assigned to Monodactylidae, has been excluded from the based on recent phylogenetic analyses that place it within Acropomatiformes, supported by molecular data resolving its affinities with other deep-sea and reef-associated percomorphs.

Genera and species

In recent phylogenetic classifications, the Monodactylidae comprises a single extant , Monodactylus Lacépède, 1801, encompassing four recognized distributed primarily in coastal marine, brackish, and occasionally freshwater habitats of the eastern Atlantic, , and western Pacific. These species exhibit variations in body proportions, fin ray counts, and geographic ranges that aid in their identification. M. sebae possesses the deepest body profile among the group, with depth exceeding standard length and a steeply angled anterior profile. M. kottelati is notable for its smaller size and specific meristic traits, including 8 dorsal spines and 28–30 dorsal soft rays, alongside a restricted distribution in the northern . Current classifications maintain all four species as valid.
SpeciesAuthority & YearCommon NameKey Distinguishing Traits & Distribution
Monodactylus argenteus(Linnaeus, 1758)Silver moonyDeep, compressed body; 7–8 dorsal spines, 27–31 dorsal soft rays; widespread in Indo-West Pacific estuaries and coastal waters.
Monodactylus sebae(Cuvier, 1829)African moonyVery deep body (depth > standard length), steep anterior profile; eastern Atlantic from to .
Monodactylus kottelatiPethiyagoda, 1991Kottelat's moonySmall adult size (to 7.8 cm SL); 8 dorsal spines, 28–30 dorsal and anal soft rays; northern (, ).
Monodactylus falciformisLacépède, 1801Full moonyRounded body form; western from to ; maximum length to 31 cm TL.

Description

Morphology

Members of the Monodactylidae family exhibit a distinctive body shape that is deep and strongly laterally compressed, often described as oval or disc-like, with standard length typically 1.2 to 2.0 times the body depth (body depth contained 1.2 to 2.0 times in standard length). This compression is particularly pronounced in species like Monodactylus sebae, where the body depth is nearly equal to the standard length, contributing to their streamlined profile for maneuvering in coastal and estuarine environments. Adults generally reach a standard length of 15–25 cm, though juveniles display a more rounded form before attaining the deeper adult morphology. The structure is a key morphological feature, with both dorsal and anal fins possessing long bases covered in scales, a trait that extends to the fin margins and distinguishes them within related perciform groups. The typically includes 7–8 short, graduated spines followed by 25–38 soft rays, while the anal fin has 3 spines and 25–38 soft rays; in M. sebae, these counts reach up to 32–38 dorsal soft rays and 36–38 anal soft rays, with the anterior portions of both fins elongated for enhanced mobility. Pectoral fins are elongated and falcate, aiding in agile swimming, whereas pelvic fins are small or vestigial in adults—often rudimentary or absent—though fully developed with multiple rays in juveniles; this reduction is a diagnostic characteristic of the family. Head morphology features moderately large eyes positioned high on the head, facilitating wide-angle vision in turbid waters, paired with a small, oblique equipped with bands of tiny conical villiform teeth on the jaws and granular teeth on the and . The is partially exposed and slightly protrusible, supporting a diet of small prey. The preopercle is smooth or finely serrated posteriorly. The is covered in small, ctenoid or scales that extend over the body, head, and bases of the median , providing a silvery sheen that aids in among light-reflecting surfaces. This scale coverage on the fins is notably extensive compared to many related families, enhancing and flexibility.

Coloration and markings

Members of the Monodactylidae family generally possess a silvery body coloration with a metallic sheen, often accented by yellow tinges along the fin edges and body margins. This reflective appearance is characteristic across , enhancing their streamlined profile in coastal and estuarine environments. Distinct markings include black or dusky tips on the dorsal and anal fins, which contribute to their visual appeal. For instance, in , the fins display prominent yellow hues with black margins, while Monodactylus sebae features silvery grey to brownish tones with four dark vertical bars that are more pronounced ventrally. Juveniles across the family often exhibit two to multiple dark vertical bars—curved or wavy—on the head and anterior body, which fade or become less distinct as individuals mature. Ontogenetic changes in coloration are evident, with juveniles showing more vivid markings and pigmentation, such as extensive on the in M. argenteus, compared to the paler, more uniform silver of adults. These shifts occur as fish transition from shallow, structured habitats to open waters, where the subdued adult tones predominate. in Monodactylidae is not pronounced, with no distinct external color or marking differences between males and females; minor variations in mature size may occur in some species, but these are subtle and not reliably diagnostic.

Distribution and habitat

Geographic range

The family Monodactylidae exhibits a primarily tropical distribution across the Indo-West Pacific and eastern Atlantic regions, spanning coastal waters from western to the western Pacific islands, including . Fossil records indicate an ancient lineage dating back to the Eocene, as evidenced by extinct genera such as Psettopsis from the Monte Bolca lagerstätten in . Among the six recognized species, has the broadest distribution, occurring throughout the Indo-West Pacific from the and , eastward across the to , , and as far east as and the . In contrast, Monodactylus sebae is confined to the eastern Atlantic, ranging from and southward to , including the . Monodactylus kottelati is more restricted, known primarily from the northern along the coasts of and eastern , with records extending to the Chilika Lagoon on India's east coast. Similarly, Monodactylus falciformis occupies the western , from the southward to in , including and Island. Schuettea scalaripinnis is endemic to the east coast of Australia from to southern , while Schuettea woodwardi occurs along the southwest coast from to .

Preferred habitats

Monodactylidae species are fishes that inhabit primarily brackish estuaries and coastal marine waters, with occasional occurrences in freshwater rivers. They are typically found at depths ranging from 0 to 12 meters in pelagic-neritic zones. These fishes prefer features such as mangroves, muddy bays, beds, tidal creeks, and silty coastal reefs, often in shallow, protected coastal areas across the and eastern Africa. They commonly form large shoals in these environments, providing opportunities for social aggregation. Monodactylidae exhibit notable adaptations to variable conditions, including tolerance to salinity fluctuations from 0 to 35 parts per thousand (ppt), enabling survival across freshwater, brackish, and full marine salinities. They favor warm temperatures between 24 and 30°C, which support their activity in tropical and subtropical coastal systems. Pollution in estuaries, including sewage and industrial runoff, poses a significant concern for their preferred habitats, contributing to degradation of mangrove and seagrass areas essential for their persistence.

Biology

Diet and feeding

Members of the Monodactylidae family exhibit an omnivorous diet, though they are primarily carnivorous, consuming a variety of small prey items including , crustaceans such as shrimps and decapods, , , and small , supplemented by and periphytic . For instance, in Monodactylus species, M. argenteus primarily ingests and , while M. sebae incorporates and shrimps alongside and other . Limited exist for Schuettea species, which have a of 3.5. This dietary flexibility supports their adaptation to dynamic estuarine environments where prey availability fluctuates. Foraging in Monodactylidae occurs primarily in shoals, facilitating group detection and capture of prey near the surface in shallow coastal and estuarine habitats. They employ a protrusible and mechanism to extend and suck in small prey items, enhancing prey selection efficiency, particularly as individuals grow larger. Juveniles specifically target , showing an ontogenic shift toward more diverse benthic and periphytic items like and leaves as they reach approximately 50 mm in length. As mid-level predators with trophic levels ranging from 3.1 to 3.9 in Monodactylus species (and 3.5 in Schuettea), Monodactylidae occupy an intermediate position in estuarine food webs, preying on lower trophic organisms while serving as forage for higher predators. Schooling behavior aids in coordinated foraging, allowing efficient exploitation of patchy and resources in these ecosystems.

Reproduction and life cycle

Members of the family Monodactylidae are oviparous fishes that undergo external fertilization without parental care, classified as nonguarders. Spawning occurs in brackish or marine environments. In tropical regions, spawning can take place year-round, with intervals of 5–10 days observed in captive conditions for species like Monodactylus sebae. Natural spawning is often influenced by environmental cues such as salinity changes, which play a critical role in reproductive success. Eggs are pelagic and planktonic, measuring 0.64–0.69 mm in diameter for M. sebae, with neutral buoyancy maintained at salinities of 25–30‰ for Monodactylus argenteus. Hatching occurs after 18–20 hours at 25–29°C, yielding larvae approximately 1.6–1.8 mm in total length. Larval stages are highly dispersive due to their planktonic nature and tolerance, which enables survival across a wide range (optimal embryonic hatching at 25–40‰ and larval growth at 20–35‰). These larvae settle in estuarine habitats, where post-larvae exhibit improved survival in lower salinities, including freshwater. Juveniles form schools in shallow coastal areas, transitioning to adult morphology by around 32 days post-hatching. is reached at 8–13 cm standard length, varying by (e.g., M. sebae at ~8 cm, M. argenteus at 13 cm). No reproductive data are available for Schuettea . Growth is rapid during the first year, with larvae reaching 5–9 mm by 23–33 days post-hatching and juveniles growing to several centimeters within months. In the wild, individuals typically live 5–8 years, though captive lifespans can extend to 7–10 years under optimal conditions.

Behavior

Monodactylids are social, schooling fishes that form shoals of several hundred individuals, particularly as juveniles and adults, which aids in predator avoidance and foraging efficiency. Small juveniles may be solitary or in small groups. M. argenteus is noted for being highly territorial. Schuettea species also form schools in coastal and estuarine waters. Distinct pairing has been observed during reproduction in M. sebae.

In aquaria

Among the species of Monodactylus commonly encountered in the aquarium trade, , known as the silver moony, stands out as the most popular due to its hardiness, widespread distribution across estuaries from to , and striking silvery sheen that provides a reflective, mirror-like quality in aquariums. This species is primarily sourced from wild collections in brackish estuarine habitats, with remaining rare despite some documented successes in controlled rearing protocols. Monodactylus sebae, the African moony, is another favored species, prized for its distinctive tall, disc-like body shape resembling freshwater angelfish during juvenile stages, which transitions to a more rounded form in adulthood. Native to eastern Atlantic coastal and estuarine waters, it is less hardy than M. argenteus and more prone to disease in captivity, though its attractive juveniles draw hobbyist interest. Like M. argenteus, M. sebae is mostly wild-caught, with attempts dating back to the late 1960s but still infrequent in commercial production. The trade in Monodactylus species has persisted for decades, with wild collections from estuaries forming the bulk of supply since at least the mid-20th century, when early import records and rearing experiments began appearing in aquarium literature. While M. argenteus and M. sebae remain readily available in the hobby trade through exporters and retailers, other congeners such as Monodactylus kottelati—a smaller species occasionally imported from Southeast Asian sources like Thailand—appear far less frequently, often limited to specialized shipments.

Care requirements

Monodactylidae species, commonly kept in aquariums, demand a spacious setup to support their active, schooling nature. A minimum volume of 400 liters (approx. 100 gallons) is advised for a small group, providing sufficient open swimming areas while incorporating some hiding spots with rocks or . conditions are essential, with a specific gravity ranging from 1.005 to 1.015 to replicate their estuarine origins; should be gradually increased for adults toward higher levels for optimal health. Temperature must be stable at 24–28°C, and between 7.5 and 8.5, using a marine salt mix rather than aquarium salt to maintain buffering capacity. In captivity, these are omnivorous and benefit from a diverse diet fed in small portions multiple times daily to match their high metabolism. High-quality flakes or pellets form the staple, augmented with frozen or live foods like and wafers; supplementing with blanched vegetables such as or peas supports digestion and overall vitality. Maintaining excellent is critical due to the family's substantial waste output from frequent feeding. Robust with strong water flow and oxygenation is necessary, paired with weekly partial water changes of 20–30% to keep nitrates below 25 mg/L and prevent or buildup. Copper-based medications should be strictly avoided, as they pose a lethal risk to these sensitive . Common challenges include vulnerability to ich (Ichthyophthirius multifiliis) outbreaks in suboptimal low-salinity environments, which can be mitigated by consistent brackish parameters and vigilant monitoring. These fish are also notorious jumpers, necessitating a securely fitted lid on the aquarium to prevent escapes. For larger species like Monodactylus sebae, additional horizontal space is recommended to accommodate their growth and activity levels.

References

  1. https://www.fishbase.se/Summary/FamilySummary.cfm?ID=333
  2. https://australian.museum/learn/animals/fishes/monodactylidae-diamondfishes-fingerfishes/
  3. https://www.marinespecies.org/aphia.php?p=taxdetails&id=151469
  4. https://www.uniprot.org/taxonomy/30853
  5. https://fishesofaustralia.net.au/home/family/45
  6. https://www.fishbase.se/summary/SpeciesSummary.php?id=59430
  7. https://etyfish.org/acanthuriformes3/
  8. https://bmcecolevol.biomedcentral.com/articles/10.1186/s12862-017-0958-3
  9. https://www.researchgate.net/publication/380184713_A_new_genus_and_two_new_species_of_Monodactylidae_Perciformes_sl_from_the_Eocene_of_northern_Italy_Bolca_Monte_Postale_and_Pesciara
  10. https://www.researchgate.net/publication/272162466_A_new_species_of_Psettopsis_Perciformes_Monodactylidae_from_the_Eocene_of_northern_Italy_Bolca
  11. https://www.ni.bio.br/1982-0224-2021-0160
  12. https://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatget.asp?genid=479
  13. https://www.fishbase.se/summary/Monodactylus-sebae.html
  14. https://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatget.asp?spid=19636
  15. https://www.fishbase.se/summary/Monodactylus-argenteus.html
  16. https://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatget.asp?spid=62148
  17. https://www.fao.org/4/ad468e/ad468eHW.pdf
  18. https://www.researchgate.net/publication/343886384_Captive_maturation_breeding_and_seed_production_of_the_brackishwater_ornamental_fish_silver_moony_Monodactylus_argenteus_Linnaeus_1758
  19. http://aquasymbio.fr/en/monodactylus-argenteus
  20. https://www.fishbase.se/summary/Schuettea-scalaripinnis.html
  21. https://www.fishbase.se/summary/Schuettea-woodwardi.html
  22. https://www.iucnredlist.org/species/166925/46644370
  23. https://www.fishbase.se/summary/Monodactylus-argenteus
  24. https://www.sciencedirect.com/science/article/abs/pii/S0044848621014861
  25. https://www.researchgate.net/publication/238383383_Feeding_ecology_and_ontogenic_diet_shifts_of_juvenile_fish_species_in_an_inverse_estuary_The_Sine-Saloum_Senegal
  26. https://www.sciencedirect.com/science/article/abs/pii/S0272771407003009
  27. https://www.algaebarn.com/blog/advanced/3-brackish-fish-for-the-marine-aquarium/
  28. https://www.fishbase.se/Reproduction/5807
  29. https://www.jstage.jst.go.jp/article/jji1950/23/4/23_4_208/_pdf
  30. https://www.researchgate.net/publication/352530013_Effects_of_salinity_amendments_on_the_embryonic_and_larval_development_of_a_tropical_brackishwater_ornamental_silver_moony_fish_Monodactylus_argenteus_Linnaeus_1758
  31. https://onlinelibrary.wiley.com/doi/10.1111/are.14816
  32. https://ruspoj.com/0042-8752/article/view/681511
  33. https://theaquariumparadise.com/fishes/silver-moony
  34. https://www.aquariumindustries.com.au/wp-content/uploads/2015/03/Mono-Argent.pdf
  35. http://brackishfaq.blogspot.com/2016/08/monos-family-monodactylidae.html
  36. https://www.aquariumglaser.de/en/tag/monodactylus-en/
  37. https://www.amazonasmagazine.com/2016/07/14/friday-photospread-captive-bred-mono-sebae/
  38. https://www.aquariumglaser.de/en/25-perchlike-fishes/monodactylus-sebae-2/
  39. https://www.aquariumglaser.de/en/32-all-the-rest/monodactylus-kottelati-2/
  40. https://www.liveaquaria.com/product/996/?pcatid=996
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