Dermongenys collettei or the Pygmy halfbeak belongs to a group of halfbeaks that are widely distributed across Southeast Asia [1] . As the halfbeak name implies, these fishes have an unusual lower jaw that is noticeably longer and protrudes beyond their upper jaw. This elongated lower jaw contains sensory receptors for the fish to sense its surroundings. The half-beak condition of these fishes become more prominent as the fish matures [2]. Males Dermogenys are known to be aggressive towards each another, hence members of this genus are sometimes used as fighting fishes [3]. Pregnant females of Dermogenys collettei give birth to live young that resembles a miniature adult, but without the prominent asymmetrical beak condition [4]. Recent phylogenetic studies suggest that this half-beak form is the basal condition within the taxon Beloniformes.

Name

Scientific name [5]

Dermogenys collettei Meisner, 2001

Synonyms

Dermogenys pusillus Herre, 1944
Dermogenys pusilla Meisner & Burns, 1997

Common/Vernacular names

English

Pygmy halfbeak
Malayan pygmy halfbeak
Sunda pygmy halfbeak

Malay

Ikan Julong (not species specific) [3]

Chinese

(not species specific) [3]

For more information on identification, click here.

Dermogenys collettei (Photo: Wilfred and Christopher (C))

Biology

Feeding habits

Dermongenys collettei are surface-dwellers that feed mostly on small floating larvae and adult insects that have drifted by or landed onto the water surface [6]. A member of the genus, Dermogenys pusilla, was observed to prey fairly extensively on mosquito larvae, flies (dipterans), ephemeropterans (mayflies) and hymenopterans (ants)[7] [18]. These fishes were also observed to approach prey item from the side of the jaws rather than the front [8]. Studies on Dermogenys pusilla showed that the elongated lower jaws of this group of halfbeaks contain mechanoreceptive neuromasts to detect movements, and may also contain taste buds for sensing chemicals [4].


Dermogenys collettei feeding on food items on the surface (Video: Wilfred (C))	Dermogenys collettei capturing food from side of mouth (Photo: Wilfred (C))

Behaviour

Dermogenys collettei are gregarious surface feeders that are often found together near the banks of water bodies [6]. Aggressive behaviour between male fishes are frequently documented from species in this genus that are sold in the aquarium trade, such as Dermogenys pusilla. Male fishes display a variety of combative behaviour such as threatening postures, biting, mouth fighting and chasing rivals. These fishes may also lock jaws during fights. Male fishes were found to display a dominance hierarchy in aquarium settings where only the dominant male is allowed near the female [4].


A male Dermogenys collettei defending its territory (Video: Wilfred (C))	Two male Demogenys pusilla fighting (Video: Youtube)

Reproduction

The major elements of courtship for Dermogenys begin with males swimming towards the female and may involve nipping of her fins. Fin nipping may induce the female to stop or slow down her movement, hence giving the male a chance to copulate. The copulation process for Dermogenys occurs very quickly, where male fishes were observed to bend their body around the female and pushes onto her. Unreceptive females were observed to threaten and even attack her suitors. The specific process of insemination is unknown, likewise whether the spermatozuegmata (sperm packet) is deposited externally
on, near or into the genital opening of the female by the male's andropodium (modified anal fin) [4].


A male Dermogenys collettei courting female fishes (Video: Wilfred (C))	Unreceptive female Dermogenys pusilla fighting off a male suitor (Video: Youtube)

Unlike most fishes, members of the genus Demogenys are viviparous, where the fish produce live young instead of eggs from within the body. Five unique forms of viviparity (Type 1-5) have been observed in freshwater halfbeaks and Dermogenys collettei display the type 1 form, where the whole gestation period is intrafollicular [5]. For more information on freshwater halfbeak viviparity, click here.


Female Dermogenys collettei with new born fry (Photo: Wilfred (C))	New born Dermogenys collettei (Picture: Wilfred & Christopher (C))

Growth

Larval halfbeaks have short jaws without prominent asymmetrical beak condition. As the fish matures, the lower jaw elongates to form the half-beak condition [9].

Preserved specimens of Dermogenys collettei showing jaw development from; A) Larval stage; B) young juvenile; C) juvenile; D) adult (Photo: Wilfred & Christopher (C))

Habitat

Dermogenys collettei are found in small streams and ponds ranging from fresh to brackish water in both forested and open areas. Fishes occupy the water surface and are frequently found near to the banks of water bodies. Specimens caught in Brunei were found in mangrove streams with acidic water of pH 3.8 [6][10].


Stream with Dermogenys collettei found in both open and forested areas (Photo: Wilfred (C))	Underwater view of Dermogenys collettei stream habitat (Photo: Wilfred (C))

Distribution

Local

Two species of halfbeaks are found in the freshwater streams in Singapore [6]. For more information on identification, click here.

Local populations of Dermogenys collettei are found in:

Central Catchment Nature Reserve (CCNR)

Western Catchment area

Recorded in Kallang river before the construction of Marina Barrage [23]

Local populations of Hemirhamphodon pogonognathus:

only in shaded forest streams in the CCNR

Dermogenys collettei are usually found in streams along the periphery of CCNR while Hemirhamphodon pogonognathus are usually found deeper in the reserve

A) Dermogenys collettei; B) Hemirhamphodon pogonognathus (Photo: Wilfred (C))

Local Dermogenys collettei distribution (Map outline adapted from Wikipedia Link

Global

About 10 members of the genus Dermogenys and 6 members of the genus Hemirhamphodon are found across Southeast Asia [10] [11].

Dermogenys collettei is found in many parts of Southeast Asia including:

Singapore

Brunei

southern Peninsula Malaysia

Sarawak

northwestern Kalimantan

Sumatra

Distribution of Dermogenys collettei (Map:Wilfred (Information adapted from Meisner, 2001))

Description

Dermogenys collettei has a greyish slender body that grows to about 6 cm. Mature female fishes are larger than males. The dorsal fin of Dermogenys collettei originates behind the anal fin origin and may have red markings [6].

Adult female and male Dermogenys collettei (Photo: Wilfred & Christopher (C))

Lateral view of Dermogenys collettei (Photo: Wilfred and Christopher (C))

Jaw Jaw of adult halfbeaks are clearly asymmetrical Jaw morphology these fishes appear to be correlated with diet, where halfbeaks feed on small floating food/prey items [12]
	Jaw of Dermogenys collettei (Photo: Wilfred and Chrisopher (C))

Upper Jaw Upper jaw of halfbeaks help to clamp down on prey Dermogenys possess a unique row of teeth located behind the rows of outer teeth that extend medially in a concave row to approximately half the length of the premaxilla [10] [20]
	Oral dentition on premaxilla plate (upper jaw) of Dermogenys collettei with outline on half of the upper jaw (Photo: Wilfred (C))

Lower Jaw The lower jaws of halfbeaks contain mechanoreceptive neuromasts to detect movements,and may conatain taste buds or sensing chemicals [4]. The lower jaw of some individuals may be broken due to injury
	A) Tip of lower jaw of Dermogenys collettei; B) Halfbeak with lower jaw broken (Photo: Wilfred (C))

Eye Ultraviolet-sensitive cones were found in the retina of Dermogenys pusilla, suggesting that vision may be important for courtship [4][13]
	Eye of Dermogenys collettei (Photo: Wilfred & Christopher (C))

Nasal Fossa A groove in which the nostril opens The nasal barbel protrudes from the nasal fossa Nasal fossa of internally fertilized halfbeak (Dermogenys collettei) is proportionally smaller compared to marine halfbeaks [10]
	Nasal fossa of halfbeaks, reflected as a small ring; A) Dermogenys collettei; B) Marine halfbeak(Photo: Wilfred (C))

Nasal Barbel Olfactory organ of the fish for detecting chemicals in the water (sense of smell) Nasal barbel of internally fertilized halfbeak is elongated while those of marine halfbeak is flat (spatulated) [10]
	Nasal barbel of halfbeaks; A) Dermogenys collettei; B) Marine halfbeak (Photo: Wilfred (C))

Anal Fin Female Dermogenys collettei has unmodified anal fin The modified anal fin of male viviparous halfbeaks is called an andropodium or gonopodium, where the first five fin rays on the anterior end of anal fin have a posterior curve, and are elongated and thickened Male anal fin rays characteristic: 1st fin ray: short and broad 2nd fin ray: elongated, terminal end possess aspiculus with lateral spine on each side (tridens flexibilis) 3rd-5th fin ray: movable, hidden during resting position in a skin fold (crytoplica) [4][10]
	Anal fin of Dermogenys collettei with with first 5 fin rays numbered; A) Retracted anal fin of male andropodium;B) Extended anal fin of male andropodium; C) Anal fin of female (Photo: Wilfred & Christopher (C))

Diagnosis

Identification of local halfbeaks

Dermogenys collettei: anal fin originates before the dorsal fin origin

Hemirhamphodon pogonognathus: anal fin originates behind dorsal fin, presence of a fleshy tip on the lower jaw that curves downward [6]

Comparison of the origin of anal fin; A) Dermogenys collettei; B) Hemirhamphodon pogonognathus (Photo: Wilfred (C))

A) Dermogenys collettei with no fleshy tip on jaw; B) Hemirhamphodon pogonognathus with fleshy tip on lower jaw (Picture: Wilfred (C))

Genus diagnosis (For more information including diagrams on genera and species description, click here)
Derrnogenys can be distinguished from other genera in Hemiramphidae by [10]

unique row of teeth located behind the rows of outer teeth that extend medially in a concave row to approximately half the length of the premaxilla
expanded endopterygoid
shortened, expanded autopalatine
distinct geniculus on second anal-fin ray in males beginning at segment three or four
gestation is entirely intrafollicular
large spermatozeugmata due to the mode of spermatogenesis in which the spermatid nuclei become arranged in one layer evenly around the periphery of spermatocysts.

Species diagnosis [10]
The anal fin structure of male Dermogenys collettei is closest to that of Dermogenys pusilla and can be distinguished by:

Thicker spiculus divided into 4-6 segments (vs. <3)
Proximal segments 4-6 of second anal-fin ray in males noticeably thicker along anterior edge

Diagrammatic illustration of the andropodium of a male Dermogenys (Adapted from Meisner & Collette, 1998 [14] , illustration by Keiko Hiratsuka Moore and with approval from the Raffles Bulletin of Zoology)

Trade

Aquarium

Dermogenys are quite commonly traded as aquarium fishes and some of the more common species would include Dermogenys pusilla, Dermogenys siamensis and Dermogenys sumatrana [15]. However, different species are frequently traded under the umbrella name of Dermogenys pusilla, leading to confusion over species identity [16]. Names like 'Golden' or 'Sliver' halfbeaks' are given depending on the colouration of the fish. In some countries such as Thailand, Dermogenys are also used as fighting fishes for gambling [3].

Silver Halfbeak (Photo: Wilfred (C))

Food

Dermogenys are commonly consumed by locals in Cambodia where the fish was found to be high in vitamin A [22].

Dermogenys collettei (Photo: Wilfred (C))

Taxonavigation

Animalia

Chordata
- Vertebrata
  - Actinopterygii
    - Neopterygii
      - Beloniformes
        Belonoidei
        Hemiramphidae
        Zenarchopterinae
        Dermogenys[17]

Actinopterygii: ray-finned bony fishes

Beloniformes: includes halfbeaks, needlefishes, flying fishes,ricefish and sauries

Hemiramphidae: all the species of halfbeak

Zenarchopterinae: fresh and brackish water halfbeaks, including halfbeaks that practise internal fertilisation

Halfbeaks and needlefishes belong to the same taxon Beloniformes

The upper jaw of halfbeaks is considerably shorter than the lower jaw

The jaw of juvenile needlefishes resembles that of halfbeaks, where the lower jaw is longer than the upper jaw

In adult needlefishes, the upper and lower jaw are similar in length

Recent phylogenetic studies suggest that the 'half-beak' condition in Hemiramphidae is the basal condition, while the the jaw morphology of needlefishes are derived characteristic [9] [19]

A) Jaw of Dermogenys collettei; B) Jaw of a needlefish (Photo: Wilfred & Christopher (C))

Taxonomy

Relevance
Finding out the evolutionary relationship between different species offers insight to speciation events that have occurred. In addition, information on the evolutionary history of organisms can be used as a criterion in conservation. Conserving an area with many different groups of organisms not only helps preserve a wider range of different species, but also their evolutionary history. Hence, areas with only a single or few groups of closely related organisms should have a lower conservation priority than areas with many different groups of organisms.

Meisner, 2001 performed a phylogenetic analysis on 28 taxa (10 species of Dermogenys and 13 species of Nomorhamphus) based on a data matrix comprising of 45 characters and constructed a strict consensus phylogenetic tree using the branch and bound option in PAUP [10]. Nested within node A, the monophyly of Dermogenys stricto sensu, is supported by 3 characters:

single row of teeth located behind the rows of outer teeth that extend medially in a concave row to approximately half the length of the premaxilla

melanophores anterior to anal fin, occur as a distinct spot in females

well defined geniculus on second anal fin ray of males

The genera (Dermogenys) is divided into 2 clades; Dermogenys pusilla group (Node B) and Dermogenys orientalis group (Node C). Dermogenys collettei is nested within the Dermogenys pusilla species group clade (Node B), sharing 2 common characters:

epibranchial four of the gill arches curved slightly at mid-length with proximal articular surface slightly expanded

type I form of viviparity

The data used in this study was unable to determine the relationship between species within a clade. More data such as using DNA barcoding may be needed to provide better resolution to the relationship between sister taxa [21].

Simplified phylogenetic tree of Dermogenys (Diagram: Wilfred (Adapted from Meisner, 2001))

Type information

A holotype is an important specimen which the formal description of a species is based on, and should possess the typical characteristics of that particular taxon. Referring to holotype specimen is therefore the best way to identify unknown specimens. Due to the importance of holotype specimens, designating the correct specimen as the holotype is extremely important for taxonomists. A paratype is another specimen of the same type series not designated as the holotype, and there can be multiple paratype specimens.

The holotype for Dermogenys collettei is collected from Kuching, Sarawak in 1994. It is kept in the Raffles Museum of Biodiversity Research (RMBR), specimen number ZRC 37790, in Singapore. The paratype (a female) is collected with the holotype and is also stored in the RMBR, specimen number ZRC 46161 [10].

Preserved specimen of Dermogenys collettei (Photo: Wilfred and Christopher (C))

Conservation

Dermogenys collettei is not yet assessed by IUCN Red List. Some species from the genus Dermogenys that are in the Red list includes:

Dermogenys burmanica (Least Concern)

Dermogenys siamensis (Least Concern)

Anthropogenic activities are major threats to some freshwater halfbeaks from the genus Dermogenys and Nomorhamphus [24]. As these fishes are commonly traded, the source of these fishes should be monitored to ensure sustainable catch. More research are therefore required to protect these unique fishes.

Dermogenys collettei (Photo: Wilfred (C))

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Literature and References

1. Meisner, A. D. & Burns, J. R. 1997. Testis and andropodial development in a viviparous halfbeak, Dermogenys sp. (Teleostei: Hemiramphidae). Copeia. 1997(1): 44-52.

2. Collette, B. B., McGowen, G. E., Parin, N. V. & Mito, S., 1984. Beloniformes: development and relationships. In: Mosher, H. G., Richards, W. J., Kendall, A. W. & Richardson, S. L., eds. Ontogeny and systematics of fishes. American Society of Ichthyologists and Herpetologists Special Publication, p. 335-354.

3. Lim, K. K. P. & Ng, P. K. L., 1990. A guide to the freshwater fishes of Singapore. The Science Centre, Singapore, p. 70.

4. Greven, H., 2010. What Do we know about reproduction of internally fertilizing halfbeaks (Zenarchopteridae)? In: Uribe, M. C. & Grier, H. J., eds. Viviparous Fishes II. New Life Publications, Homestead, Florida.

5. Meisner, A. D. & Burns, J. R., 1997. Viviparity in the halfbeak Genera Dermogenys and Nomorhamphus (Teleostei: Hemiramphidae). Journal of Morphology. 234: 295–317.

6. Baker, N. & Lim, K. K. P., 2008. Wild animals of Singapore. Draco Publishing and Distribution Pte Ltd, Singapore, p. 40.

7. Usman, S. & Soemarlan, S., 1974. Pengamatan di laboratorium mengenai ikan-ikan pemakan jentik nyamuk. Buletin Penelitian Kesehatan. 2.

8. Greven, H., 2006. Viviparous halfbeaks. Notes on structural peculiarities, feeding, and reproduction. Biologie der Aquarienfische. Tetra Verlag GmbH, p. 271-296.

9. Lovejoy, N. R., Iranpour, M. & Collette, B. B., 2004. Phylogeny and Jaw Ontogeny of Beloniform Fishes. Integrative and Comparative Biology. 44: 366–377.

10. Meisner, A. D., 2001. Phylogenetic systematics of the viviparous halfbeak genera Dermogenys and Nomorhamphus (Teleostei: Hemiramphidae: Zenarchopterinae). Zoological Journal of the Linnean Society. 133: 199-283.

11. Catalogue of Life. 2012. Available online at: http://www.catalogueoflife.org/col/search/all/key/Hemirhamphodon/match/1 [Accessed on 25th October 2012]

12. Boughton, D. A., Collette, B. B. & Mccune, A. R., 1991. Heterochrony in jaw morphology of Needlefishes (Teleostei: Belonidae). Systematic Zoology. 40(3): 329-354

13. Reckel, F., Melzer, R. R., Parry, J. W. L. & Bowmaker, J. K., 2002. The retina of five atherinomorph teleosts: Photoreceptors, patterns and spectral sensitivities. Brain, Behaviour and Evolution. 60:249-264.

14. Meisner, A. D. & Collette, B. B., 1998. A new species of viviparous halfbeak, Dermogenys bispina (Teleostei: Hemiramphidae) from Sabah (North Borneo). The Raffles Bulletin of Zoology. 46: 373-380.

15. Monks, N. Halfbeaks: Family Hemiramphidae. Available online at: http://www.wetwebmedia.com/ca/volume_4/V4I1/halfbeaks/Halfbeaks.htm [Accessed on 25th October 2012]

16. Monks, N. 2011. 7 forgotten livebearers. Tropical Fish Magazine. Available online at:
http://www.tfhmagazine.com/details/articles/7-forgotten-livebearers-full-article.htm [Accessed on 26th October 2012]

17. Encyclopedia of Life. Dermogenys collettei. Available online at: http://eol.org/pages/210958/names [Accessed online on 25th October 2012]

18.Ward-Campbell, B. M. S., Beamish, F. W. H. & Kongchaiya, C., 2005. Morphological characteristics in relation to diet in five coexisting Thai fish species. Journal of Fish Biology 67: 1266-1279.

19. Lovejoy, N. R., 2000. Reinterpreting recapitulation: Systematics of Needlefishes and their allies (Teleostei: Beloniformes). Evolution. 54(4): 1394-1362.

20. Greven, H., Wanninger, A. C. & Clemen, G., 1997. Dentigerous bones and dentition in the hemiramphid fish Dermogenys pusillus (Atheriniformes, Teleostei). Annals of Anatomy-Anatomischer Anzeiger. 179(1): 21-32.

21. de Bruyn, M., Grail, W., Barlow, A. & Carvalho, G. R., 2010. Anonymous nuclear markers for Southeast Asian halfbeak fishes (Dermogenys). Conservation Genetics Resources. 2(1): 325-327.

22. Roos, N., Chamnan, C., Loeung, D., Jakobsen, J. & Thilsted, S. H., 2006. Freshwater fish as a dietary source of vitamin A in Cambodia. Food Chemistry. 103: 1104-1111.

23. Tan, H. H., Low, M. E. Y. & Lim, K. K. P., 2010. Fishes of the Marina basin, Singapore, before the erection of the Marina Barrage. The Raffles Bulletin of Zoology. 58(1): 137-144.

24. IUCN 2012. IUCN Red List of threatened species. Version 2012.2. Available online at: http://www.iucnredlist.org/search [Accessed online on 15th December 2012]

Table of Contents

Introduction

Name

Biology

Feeding habits

Behaviour

Reproduction

Growth

Habitat

Distribution

Local

Global

Description

Diagnosis

Identification of local halfbeaks

Trade

Aquarium

Food

Taxonavigation

Taxonomy

Type information

Conservation

Comments

Links

Literature and References