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Carinotetraodon borneensis (REGAN, 1903)

SynonymsTop ↑

Tetraodon borneensis Regan, 1903

Etymology

Carinotetraodon: from the Latin carina, meaning ‘keel-shaped, shell’ and generic name Tetraodon, here used as a suffix.

borneensis: ‘of Borneo’.

Classification

Order: Tetraodontiformes Family: Tetraodontidae

Distribution

Type locality is given simply as ‘Sarawak state, Borneo, East Malaysia’, and this species is known only from southern Sarawak, Malaysia (Borneo) with confirmed records from the Sarawak, Sadong and Rajang river systems.

Habitat

Likely to inhabit marginal zones with submerged terrestrial or aquatic vegetation.

Maximum Standard Length

40 – 45 mm.

Aquarium SizeTop ↑

An aquarium with base dimensions of 75 ∗ 30 cm  or equivalent is suitable for a pair or trio, but something larger would be required for a group.

Maintenance

Best kept in a densely-planted aquarium with floating vegetation and driftwood roots or branches to diffuse the light as it’s normally quite shy in brightly-lit surroundings.

If you wish to raise fry the addition of fine-leaved aquatic moss such as a Taxiphylum sp. is advisable (see ‘Reproduction’).

The water should be well-oxygenated with a degree of movement.

Do not add this fish to a biologically immature set-up as it can be susceptible to swings in water chemistry, and weekly water changes of 20-30 % aquarium volume should be considered mandatory.

Water Conditions

Temperature20 – 28 °C

pH6.0 – 7.5

Hardness36 – 215 ppm

Diet

Carinotetraodon spp. prey on aquatic molluscs and crustaceans, and should be offered a meaty diet comprising live and frozen bloodworm, ArtemiaMysis, chopped prawn/shrimp, etc.

They should also be fed live snails on a regular basis in order to prevent their well-developed crushing teeth, which grow continuously, from becoming too long.

In the aquarium fish fry and small freshwater shrimp are also likely to be consumed.

Behaviour and CompatibilityTop ↑

Less aggressive than some members of the genus but nevertheless best maintained alone or alongside a group of peaceful, schooling cyprinids of a size large enough to escape predation but small enough that they offer no competition or threat.

It’s only loosely gregarious, males in particular tending to protect their individual space, but a group can be maintained provided sufficient cover is available.

Sexual Dimorphism

In males body colour is greyish and faintly mottled, and this is not distinctly separated from the whitish belly and underside of the head, rather merging into it gradually.

There is a thin, yellowish stripe extending posteriorly from the eye to the caudal peduncle, plus a similarly-coloured, chevron-shaped marking on the dorsal surface and a narrow interorbital bar.

The extremities of the chevron reach the upper posterior edge of the eye but are not in contact with the interorbital bar, while a second, smaller chevron extends anteriorly from the dorsal-fin base.

All males possess a broad, red mid-ventral stripe and the dorsum is also sometimes red.

The pectoral-fin is hyaline with a black base, anal-fin hyaline and sometimes tinged with red, dorsal-fin red with a dark marking at the base and caudal-fin bluish to yellowish or greyish with black and white distal bands.

No females were included in the redescription of the species by Tan (1999) but aquarium specimens traded as such possess a similar pale lateral stripe to that of males but it is broader, sometimes interrupted and may contain a few irregular brownish markings.

The chevron markings are also present with the larger also broader than in males, and the remainder of the body is punctuated with irregular pale blotches.

The belly is whitish but without brownish markings, and there is a darker blotch just anterior to the anal-fin origin.

The fins are mostly hyaline but the dorsal contains faint stripes while the caudal is yellowish with reticulated markings and several dark bars.

The eye is red in both males and females, but sometimes appears greenish-blue in the former.

Reproduction

Unrecorded. The congener C. irrubesco is known to scatter its eggs among vegetation and does not exhibit any parental care.

NotesTop ↑

This species is relatively uncommon in the aquarium hobby but is available on occasion, sometimes mixed in among shipments of the congener C. salivator.

These two can be told apart by the fact that C. salivator possesses a series of distinct dark bars on the head and body in both sexes, a colour pattern unique within the genus.

It’s also similar to C. irrubesco and C. lorteti but can be told apart from the former by males possessing a  bluish to yellowish or greyish caudal-fin with black and white distal bands(vs. red) and the latter by lacking (vs. possessing) a black blotch at the base of the anal-fin.

It can be further distinguished from all congeners by the following characters: 12-13 dorsal-fin rays (mode 12); 11-13 anal-fin rays (mode 11 or 13); 16 pectoral-fin rays; 12 caudal-fin rays; length of dorsal-fin base 12.5-14.0 % SL; length of anal-fin base 10.2-10.9 % SL; males with a black blotch at base of dorsal-fin; base of pectoral-fin black; certain other aspects of colour pattern (see ‘Sexual Dimorphism’).

The genus Carinotetraodon was first proposed by Benl (1957) to accommodate C. chlupatyi Benl, 1957, currently considered a synonym of C. lorteti.

Member are distributed in southern India and Southeast Asia, and differ from all other tetraodontids by the presence of mid-dorsal and mid-ventral ridges in males.

These are used during courtship and threat displays and sometimes referred to as ‘keels’ by aquarists.

It’s also unique within Tetraodontidae in that males and females exhibit strong sexual dimorphism and dichromatism.

The family Tetraodontidae is the most speciose group among Tetraodontiformes and its members mostly inhabit coastal waters in South America, Central Africa, and Southeast Asia.

It’s the only tetraodontiform family in which a number of members exist and reproduce solely in freshwater and genetic evidence suggests that the timing of these invasions differed, occurring around 0–10 million years ago (MA) in South America, 17–38 MA in Central Africa and 48–78 MA in Southeast Asia.

Tetraodontids are often collectively referred to as ‘pufferfishes’ in reference to their ability to rapidly inflate their bodies with water or air when threatened.

Several species rank among the most poisonous vertebrates in the world with their internal organs, particularly the liver and gonads, containing lethal quantities of a substance known as tetrodotoxin, and in some cases this may also accumulate in the gonads during the spawning season.

The toxin is not produced by the fish themselves but by symbiotic bacteria inhabiting the viscera, and has been recorded from a number of other animals including newts, sea stars and octopi.

It’s around 100 times more potent than potassium cyanide, with ingestion of around 25 mg enough to kill a 75 kg human, and there currently exists no antidote.

References

  1. Lim, K. K. P. and M. Kottelat, 1995 - Japanese Journal of Ichthyology 41(4): 359-365
    Carinotetraodon salivator, a new species of pufferfish from Sarawak, Malaysia (Teleostei: Tetraodontidae).
  2. Parenti, L.R. and K.K.P. Lim, 2005 - Raffles Bulletin of Zoology Supplement 13: 175-208
    Fishes of the Rajang basin, Sarawak, Malaysia.
  3. Tan, H. H., 1999 - Ichthyological Exploration of Freshwaters 10(4): 345-354
    A new species of Carinotetraodon from Sumatra and Borneo and validity of C. borneensis (Teleostei: Tetraodontidae).
  4. Yamanoue, Y., M. Miya, H. Doi, K. Mabuchi, H. Sakai and M. Nishida, 2011 - PLoS ONE 6(2): e17410
    Multiple Invasions into Freshwater by Pufferfishes (Teleostei: Tetraodontidae): A Mitogenomic Perspective.

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