Carinotetraodon borneensis (REGAN, 1903)

SynonymsTop ↑

Tetrodon borneensis Regan, 1903

Etymology

Carinotetraodon: from the Latin carina, meaning ‘keel’, and the generic name Tetraodon, within which members have formerly been included.

borneensis: ‘of Borneo’.

Classification

Order: Tetraodontiformes Family: Tetraodontidae

Distribution

Known only from southern Sarawak state, Malaysia (Borneo), with confirmed records from the Sarawak, Sadong and Rajang river systems.

Type locality is ‘Sarawak state, Borneo, East Malaysia’.

Habitat

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

Maximum Standard Length

40 – 45 mm.

Aquarium SizeTop ↑

An aquarium with dimensions of 60 ∗ 30 ∗ 30 cm or equivalent should be the smallest considered.

Maintenance

This species requires a well-decorated aquarium with driftwood roots or branches plus plenty of aquatic plants, of which floating varieties can be used to provide additional shade. The addition of dried leaf litter further emphasises the natural feel and as well as offering cover brings with it development of microbe colonies which can provide a valuable early food source for fry.

Any flow from the filter should not be strong, and regular small water changes are recommended since this species is sensitive to deteriorating conditions.

Water Conditions

Temperature: 20 – 28 °C

pH: 6.0 – 7.5

Hardness: 36 – 215 ppm

Diet

Tetraodontids lack true teeth, the jawbone itself being modified into four fused toothlike structures. These grow continuously at a surprising rate, so offer regular meals of shelled invertebrates such as snails, small crab legs, cockles, etc., in order to maintain them at a reasonable length. There is some evidence to suggest that aufwuchs form a significant proportion of the natural diet, therefore it may be worth permitting or even encouraging algal growth on hard items of décor.

Additional foods can include chopped shellfish, small earthworms, and live or frozen chironomid larvae (bloodworm), Artemia, etc. Dried products should not form the principal component of the diet, although pelleted formats with a very hard consistency may prove useful.

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 is only loosely gregarious, males in particular tending to behave territorially, but a group can be maintained provided sufficient cover and space 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 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. lorteti is known to scatter its eggs among vegetation, with the male guarding the brood during incubation.

NotesTop ↑

This species is relatively uncommon in the aquarium hobby but is 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.

C. borneensis is included in a group often referred to as ‘red-eyed puffers’, which currently contains four recognised species distributed in Indochina and the Greater Sunda Islands. It can be distinguished from C. irrubesco, C. lorteti and C. salivator, the remaining members of this group, by the following combination of characters: 12-13 dorsal-fin rays; 16 pectoral-fin rays; 11-13 anal-fin rays; 12 caudal-fin rays; eyes not bulging above the head; in males dorsal-fin orangeish, black spot on dorsal-fin base present, pectoral-fin base with a black bar, anal-fin hyaline with black edge, caudal-fin greyish proximally and black with white edge distally, throat unmarked, no bars on body.

Carinotetraodon is distinguished from other genera within the family Tetraodontidae by the presence of distinctive dorsal and ventral keels in males, plus distinct sexual dimorphism in terms of both morphology and colour pattern. Tetraodontidae is the most speciose group among Tetraodontiformes and its members mostly inhabit coastal waters in South America, Central Africa, and Southeast Asia. It is the only tetraodontiform family in which a number of members exclusively inhabit 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 commonly referred to as ‘puffers’ due to the ability of many species to inflate their body to an enormous size when stressed or threatened. This is achieved by drawing water into a specialised ventral diverticulum of the stomach, although air can also be used if the fish is removed from the water. As a result of these morphological adaptations puffers swim via a unique combination of pectoral and median fin undulations referred to as ‘diodontiform’ swimming. They are also able to produce sounds by grinding the jaw/pharyngeal teeth or vibrating the swim bladder. Puffers are secondary freshwater fishes, with the majority of members exclusively inhabiting marine environments.

Other defining characters of tetraodontids include a tough skin usually covered with small spines, a beak-like dental plate divided by a median suture, a reduced gill opening anterior to the pectoral-fin base, no pelvic fins or spinous fin rays, typically short-based dorsal and anal fins, and no ribs.

Puffer flesh is toxic and can cause clinical poisoning and human mortality, although it is regarded as a delicacy in certain countries. The predominant toxin, usually either tetrodotoxin or saxitoxin, is dependant on species, geographic area, and time of year. The toxins are not produced by the fishes themselves, but by bacteria living in symbiotic association, or they are acquired via the food chain.

References

1. Regan, C. T., 1903 - Proceedings of the Zoological Society of London 1902 2(2): 284-303
   On the classification of the fishes of the suborder Plectognathi; with notes and descriptions of new species from specimens in the British Museum Collection.
2. Ebert, K., 2001 - Aqualog, Rodgau: 1-96
   The puffers of fresh and brackish waters.
3. Kottelat, M., 2013 - Raffles Bulletin of Zoology Supplement 27: 1-663
   The fishes of the inland waters of southeast Asia: a catalogue and core bibiography of the fishes known to occur in freshwaters, mangroves and estuaries.
4. 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).
5. Parenti, L.R. and K.K.P. Lim, 2005 - Raffles Bulletin of Zoology Supplement 13: 175-208
   Fishes of the Rajang basin, Sarawak, Malaysia.
6. 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).
7. 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.