Dwarf pufferfish
A side profile of an adult dwarf pufferfish against a white background, facing left and slightly upward.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Tetraodontiformes
Family: Tetraodontidae
Genus: Carinotetraodon
Species:
C. travancoricus
Binomial name
Carinotetraodon travancoricus
(Hora & K.K. Nair, 1941)[2]
Synonyms[1][2]
  • Tetraodon travancoricus
    Hora & K.K. Nair, 1941
  • Monotretus travancoricus
    (Hora & K.K. Nair, 1941)

The dwarf pufferfish (Carinotetraodon travancoricus), also known as the Malabar pufferfish, pygmy pufferfish, or pea pufferfish, is a small freshwater pufferfish endemic to Kerala and southern Karnataka in Southwest India. They are popular in aquaria for their bright colours and small size. At a maximum total length of 3.5 cm, dwarf pufferfish are one of the smallest pufferfish in the world. They closely resemble the related Carinotetraodon imitator, and the two can be difficult to distinguish. C. imitator was not recognised as a different species until 1999.

Dwarf pufferfish dwell at the bottom of heavily vegetated waterways, predating small animals. Unlike other species of pufferfish, they are found in large groups in the wild. They breed throughout most of the year, with spawning pairs producing 1–5 eggs in 1–4 day intervals. Habitat loss and overharvesting for the aquarium trade threaten wild populations of dwarf pufferfish.

Taxonomy

The dwarf pufferfish was first described as Tetraodon (Monotretus) travancoricus in 1941 by S.L. Hora and K.K. Nair,[3][4] with the type locality given as "Pamba River, Central Travancore".[2] The use of parentheses indicates Monotretus is the subgenus of Tetraodon. Carinotetraodon was considered a synonym of Tetraodon until 1978, when J.C. Tyler treated it as a valid genus in a paper about Carinotetraodon lorteti, which was an opinion followed by M. Kottelat et al. in 1993 and K.K.P. Lim and M. Kottelat in 1995.[4] The first use of "Carinotetraodon travancoricus" was in 1999 by R. Britz and M. Kottelat when first describing Carinotetraodon imitator, a superficially similar and closely related species previously mistaken for dwarf pufferfish.[4] "Carinotetraodon" is derived from the Latin word "carina" (keel-shaped, shell) and Greek words "tetra" (four) and "odous" (teeth).[5] The justification for moving to Carinotetraodon was based largely on osteological evidence and not on the presence of skin keels, which other members of the genus have, but which had not been confirmed in dwarf pufferfish until one year later in aquarium literature.[6] Specifically, dwarf pufferfish possess vertebral modifications and a reduced number of total vertebrae similar to other members of Carinotetraodon, in addition to a small size and the presence of sexual dimorphism, also found amongst other members of this genus.[4]

The following cladogram is based on molecular evidence and demonstrates the polyphyletic nature of the genus Carinotetraodon.[7][8] A polyphyletic genus is one in which members share common characteristics, but do not necessarily share an immediate common ancestor, and their placement is based on these shared traits rather than confirmed, empirical evidence. "Carinotetraodon" is represented in quotation marks to signify its polyphyletic status. Freshwater species are denoted with "FW".[7][8] The cladogram is incomplete due to the absence of species like C. imitator, which have not undergone mitogenome analyses.

The closely related Dichotomyctere nigroviridis
Tetraodontidae

Auriglobus modestus

Leiodon cutcutiaFW

"Carinotetraodon" salivatorFW

"Carinotetraodon" lortetiFW

"Carinotetraodon" irrubescoFW

Pao palembangensisFW

Pao cochinchinensisFW

"Carinotetraodon" travancoricusFW

Dichotomyctere nigroviridis

Dichotomyctere ocellatus

Pelagocephalus marki

Canthigaster coronata

Canthigaster rivulata

Canthigaster jactator

Canthigaster valentini

Chelonodon pleurospilus

Chelonodon patoca

Tetraodon miurusFW

Tetraodon mbuFW

Description

A dwarf pufferfish in an aquarium, displaying its iridescent patches.
Dwarf pufferfish have dark, iridescent patches on their flanks and dorsal surfaces

The maximum documented size is 3.5 cm (1.4 in) total length (TL),[9] with individuals typically reaching less than 2.5 cm (0.98 in) TL,[5] making dwarf pufferfish one of the smallest pufferfish in the world.[8][10] Both sexes are primarily greenish-yellow, with dark green to brown-black iridescent patches on the flanks and dorsal surface. Patterns and colouration vary considerably between individuals. Their pectoral fins are short, fan-shaped, and described as "slightly emarginate", that is to say, slightly indented at the tip. The dorsal and anal fins are situated opposite each other toward the posterior of the fish, both short and round, while the caudal fin is larger than the other fins and truncate, in that it terminates in a more-or-less vertical edge. Their bodies are round and oblong.[2][11] As with other members of the genus, sexual dimorphism is apparent in mature fish, with males being more brightly coloured than females[10] and having a yellow ventral surface.[12] Males can also have a dark stripe down the centre of their pale belly and iridescent, blue "eye wrinkle" patterns that females do not have. Females are more rounded, tend to be larger than males, and may have more small spots between their larger dark markings. Their abdomens are white, and they may have a yellow patch on their throat.[12]

Natural defenses

All pufferfish can inflate, or "puff up", their bodies by quickly ingesting large amounts of water (or air when necessary) into their highly elastic stomachs.[13][14] Inflating tires pufferfish and can put them at greater risk of predation.[14] Like many other pufferfish, in the absence of scales, dwarf pufferfish have skin spines on most of their body.[4][6][15] These spines become erect when the fish is inflated. These characteristics are anti-predator adaptations that make the fish difficult to swallow or bite. Biologists believe these adaptations evolved because of the slow swimming speeds of pufferfish.[13]

Though many freshwater pufferfish accumulate saxitoxin in their organs due to their consumption of specific cyanobacteria present on or in their food sources, no research has been published confirming or denying the presence of this neurotoxin in dwarf pufferfish.[12]

Resemblance to Carinotetraodon imitator

Carinotetraodon imitator is a species of related pufferfish closely resembling dwarf pufferfish. They are of similar size, shape, patterns, and colouration. Both species are found within the same region and may be sympatric, possibly inhabiting the same waters. Until 1999, C. imitator was mistaken as the same species, and the two could be found together in aquaria and were widely available in the international aquarium trade, both sold as dwarf pufferfish. Dwarf pufferfish can be distinguished from their congener (a member of the same genus), as C. imitator have smaller, faint blotches compared to dwarf pufferfish, as well as greatly reduced body spination. Male dwarf pufferfish have a darker yellow colouration and an iridescent "eye wrinkle" not found in males of C. imitator.[4]

Distribution and habitat

Global distribution[16]

Although closely related to marine pufferfish, they are not found in salt water, and reports to the contrary are based on misidentification.[17] Dwarf pufferfish are one of only 27 known species of Tetraodontidae adapted to freshwater.[18] They are a potamodromous species,[19] meaning they migrate within freshwater river systems,[20] and are endemic to rivers, lakes, and estuaries[21] in Kerala and southern Karnataka in the Western Ghats of Peninsular India.[1][22][3] They can be found in waters with a pH of 7.5–8.3 and temperatures of 22–28 °C (72–82 °F).[5] Inhabiting heavily vegetated waters with beds of gravel and rock or clay loam with silt and sand,[21] the species is reported from 13 rivers in Kerala,[23] lakes such as Vembanad,[24] the Nilambur harbours,[22] and Kallar Stream, part of the Neyyar Wildlife Sanctuary.[21] They have been reported as rare in Bharathapuzha[25] and the Nilgiri Biosphere Reserve.[26] The species was also found in inundated brickyards in Puthukkad,[27] as well as ditches, ponds, irrigation channels, and artificial tanks or abandoned water bodies in paddy fields. Their presence in small, isolated water bodies is likely due to unintentional dispersal by waterfowl.[28]

Conservation status

Several researchers have considered the species endangered, though with no rationale provided.[29][30][31] The dwarf pufferfish is officially classified as vulnerable on the IUCN Red List due to declining populations because of damming, indiscriminate deforestation for agriculture, pollution from wastewater, and, primarily, overfishing for the aquarium trade.[1][23] In 2010, some researchers estimated that the population would decline by 30–40% from 2005 to 2015,[1][29] while others estimated it had already declined by the same amount between 2005 and 2010.[32]

Diet and behaviour

Dwarf pufferfish are euryphagous carnivores in that they consume a wide variety of animals. Dwarf pufferfish favour insect larvae but will rely on crustaceans and annelids as alternate feed when the availability of preferable prey decreases.[33] Their diet in the wild mainly consists of small animals such as water fleas, rotifers, copepods, and seed shrimp, and aquatic larvae such as those of Odonata, Hemiptera, mayflies, and flies, with some amounts of plant matter, largely diatoms and green algae.[21][33] Sand and detritus, presumably ingested by mistake when feeding on small, bottom-dwelling animals, have also been found in their gut.[21][33]

Several wild dwarf pufferfish are viewed from above in yellowish water
Dwarf pufferfish shoaling in the wild, seen from above

In captivity, dwarf pufferfish benefit from a varied diet and will eat small freshwater snails, shrimps, as well as foods like frozen mussel meat or other frozen shellfish. They will also readily eat live foods such as red and white mosquito larvae and other small animals they would predate in the wild.[34] Dwarf pufferfish are commonly associated with plants in the genus Cabomba, and the presence of these plants has been shown to reduce mortality among captive specimens.[23]

Dwarf pufferfish are a slow-swimming,[28] demersal, or bottom-dwelling, species.[5] Unlike many pufferfish species, which are primarily solitary and potentially aggressive or territorial between conspecifics (members of the same species),[35] dwarf pufferfish are found in large shoals, occasionally consisting of hundreds of individuals.[27] They are found mainly during the summer months (January to May) and rarely during the rainy season.[27] Shoaling fish experience stress or weight loss when kept in solitude or in groups too small.[36][37]

Reproduction

In the wild, males with ripe gonads have been found during all months of the year but December and January, with the peak spawning period extending from May to August, concurring with the South-West monsoon period.[38] Within the Pamba River, the minimum size at which half the population becomes sexually mature is approximately 1.83 cm (0.72 in). Environmental and dietary conditions may influence the maturation rate of individuals.[38]

Left-side view of a juvenile against a blank background.
Juvenile

The mid-dorsal and mid-ventral skin ridges of males become brown in colour during the spawning season. The belly of the female will swell, and the courting male will frequently chase the female and nibble at its belly. The female will then search for a suitable location to spawn while the male chases away other males.[18] In the aquarium, dwarf pufferfish are often plant-spawners, laying eggs in plants, including java moss, or on the substrate hidden within plants.[39] A female will scatter approximately 1–5 eggs, 1.43 mm (0.056 in) in mean diameter. The eggs are adhesive and appear transparent and round, with a mass of small oil globules. After laying, the eggs are then fertilized externally by the male.[18] Spawning has been observed in the evening, with the female resting on the spawning site and the male slowly approaching. After spawning, both fish will leave the site. The male will then quickly return to guard the eggs.[18] Sneaking ejaculation by other males has also been observed.[18] The pair may spawn multiple times in 1–4 day intervals.[18]

Eggs hatch after five days at 27 °C (81 °F), with larvae and fry in captivity initially fed infusoria, Brachionus (a genus of rotifers), frozen bloodworms, and brine shrimp when they are a week old.[39][18] There is little information on what the larvae eat in the wild.[10] Hatched larvae are a mean of 3.15 mm (0.124 in) total length, with eyes incompletely developed and the body a red-brown. The yolk sac is consumed in four days, and the larvae commence swimming after six days, at which point their eyes are completely developed.[18]

There is no information available on the lifespans of these fish in the wild, but aquarists report specimens live for approximately five years in captivity.[12]

Association with humans

When first described in 1941, K. Nair noted that dwarf pufferfish were a favourite of children, who would catch and use the fish as playthings.[2] They were regarded as "frog tadpoles" by local fishermen[27] and otherwise given little consideration. They are of no interest to fisheries,[9] are not a food fish, and are only valued as ornamental fish in aquaria.[40][1] Dwarf pufferfish have become popular as aquarium fish thanks to their attractive colours, small size, "puppy dog eyes", and relative ease of maintenance.[10][33] The dwarf pufferfish is also one of the few aquarium fish to regularly eat small, live snails and thus can be helpful in controlling snail populations.[11]

References

  1. 1 2 3 4 5 6 Dahanukar, N. (2011). "Carinotetraodon travancoricus". IUCN Red List of Threatened Species. 2011: e.T166591A174788004. doi:10.2305/IUCN.UK.2011-1.RLTS.T166591A174788004.en. Retrieved 4 May 2022.
  2. 1 2 3 4 5 Hora, S.L.; Nair, K.K. (1941). "Notes on Fishes in the Indian Museum: XLI. New Records of Freshwater Fish from Travancore". Records of the Indian Museum. 43: 387–393. Retrieved 4 May 2022.
  3. 1 2 Devi, K.R.; Indra, T.J.; Raghunathan, M.B. (2000). "On a report of Tetradon (Monotretus) travancoricus, from south Kanara, Karnataka, India". Journal of the Bombay Natural History Society. 97 (3): 441–443. Retrieved 4 May 2022.
  4. 1 2 3 4 5 6 Britz, R.; Kottelat, M. (May 1999). "Carinotetraodon imitator, a new freshwater pufferfish from India (Teleostei: Tetraodontiformes)". Journal of South Asian Natural History. Sri Lanka: Wildlife Heritage Trust of Sri Lanka. 4 (1): 39–47. ISSN 1022-0828. Retrieved 19 May 2022.
  5. 1 2 3 4 Froese, Rainer; Pauly, Daniel (eds.) (2023). "Carinotetraodon travancoricus" in FishBase. June 2023 version.
  6. 1 2 Britz, R.; Ali, A.; Philip, S.; Kumar, K.; Raghavan, R. (October 2012). "First record from the wild of Carinotetraodon imitator in Peninsular India (Teleostei: Tetraodontiformes: Tetraodontidae)". Ichthyological Exploration of Freshwaters. 23 (2): 105–109. ISSN 0936-9902. Retrieved 1 May 2022.
  7. 1 2 Sathyajith, C.; Yamanoue, Y.; Yokobori, S.; Thampy, S.; Vattiringal Jayadradhan, R.K. (December 2019). "Mitogenome analysis of dwarf pufferfish (Carinotetraodon travancoricus) endemic to southwest India and its implications in the phylogeny of Tetraodontidae". Journal of Genetics. 98 (5): 98–105. doi:10.1007/s12041-019-1151-9. PMID 31819020. S2CID 208020436.
  8. 1 2 3 Santini, F.; Nguyen, M. T. T.; Sorenson, L.; Waltzek, T. B.; Lynch Alfaro, J. W.; Eastman, J. M.; Alfaro, M. E. (May 2013). "Do habitat shifts drive diversification in teleost fishes? An example from the pufferfishes (Tetraodontidae)". Journal of Evolutionary Biology. 26 (5): 1003–1018. doi:10.1111/jeb.12112. PMID 23496826. S2CID 25969423. Retrieved 24 October 2023.
  9. 1 2 Talwar, P. K.; Jhingran, A.G. (1991). Inland fishes of India and adjacent countries. New Delhi: Oxford & IBH Pub. Co. ISBN 9788120406391.
  10. 1 2 3 4 Klaus, Ebert (2001). The Puffers of Fresh and Brackish Water. Aqualog. pp. 19, 46–49. ISBN 3-931702-60-X.
  11. 1 2 Anna Mercy, T.V.; Gopalakrishnan, A.; Kapoor, D.; Lakra, W.S. (2007). Ornamental fishes of the Western Ghats of India. Lucknow: National Bureau of Fish Genetic Resources. pp. 227–228. ISBN 978-81-902951-8-5.
  12. 1 2 3 4 Hellweg, Mike (March 2007). "The Dwarf Puffer: A Pleasant Little Surprise". www.tfhmagazine.com. TFH Magazine. Retrieved 5 May 2022.
  13. 1 2 "Pufferfish | National Geographic". www.nationalgeograph.orc. National Geographic. 12 March 2010. Archived from the original on 29 March 2021. Retrieved 28 May 2022.
  14. 1 2 Geggel, Laura Geggel (4 December 2014). "Puffed-Up Blowfish Aren't Holding Their Breath". livescience.com. Live Science. Retrieved 18 October 2023.
  15. ↑ Shono, T.; Thiery, A.P.; Cooper, R. L.; Kurokawa, D.; Britz, R.; Okabe, M.; Fraser, G.J. (September 2019). "Evolution and Developmental Diversity of Skin Spines in Pufferfishes". iScience. 19: 1248–1259. Bibcode:2019iSci...19.1248S. doi:10.1016/j.isci.2019.06.003. PMC 6831732. PMID 31353167.
  16. ↑ Based on the following sources:
  17. ↑ Schäfer, Frank (2005). Brackish-water Fishes: All about Species, Care and Breeding. A.C.S. p. 34. ISBN 9783936027822.
  18. 1 2 3 4 5 6 7 8 Doi, Hiroyuki; Sakai, Harumi; Yamanoue, Yusuke; Sonoyama, Takayuki; Ishibashi, Toshiaki (March 2015). "Spawning of eight Southeast Asian brackish and freshwater puffers of the genera Tetraodon and Carinotetraodon in captivity". Fisheries Science. 81 (2): 291–299. doi:10.1007/s12562-014-0842-7. S2CID 255616157.
  19. ↑ Reid, Klaus (2004). Global Register of Migratory Species: From Global to Regional Scales : Final Report of the R&D-Projekt 808 05 081. Federal Agency for Nature Conservation. p. 308. ISBN 9783784338453.
  20. ↑ Gopalakrishnan, Omkar; Riede, Klaus (2004). Some observations on fish migration, with emphasis on tropical waters (Report). Federal Agency for Nature Conservation. doi:10.13140/RG.2.1.5099.0969. Retrieved 12 October 2023.
  21. 1 2 3 4 5 Prasad, G.; Sabu, K.; Prathibhakumari, P.V. (2012). "The first report of the Malabar puffer, Carinotetraodon travancoricus (Hora & Nair, 1941) from the Neyyar wildlife sanctuary with a note on its feeding habit and length-weight relationship" (PDF). Journal on New Biological Reports. 1 (2): 42–46. ISSN 2319-1104. Retrieved 6 May 2022.
  22. 1 2 Easa, P.S.; Basha, C.C. (1995). "A Survey on the Habitat and Distribution of Stream Fishes in the Kerala part of Nilgiri Biosphere Reserve" (PDF). Kerala Forest Research Report. 104. Retrieved 6 May 2022.
  23. 1 2 3 Anupama, K.M.; Harikrishnan, M. (2015). "Improved survival of Malabar puffer fish, Carinotetraodon travancoricus (Hora and Nair, 1941) in planted aquaria". International Journal of Environmental Sciences. 6 (1): 138–144. doi:10.6088/ijes.6016 (inactive 10 October 2023). ISSN 0976-4402.{{cite journal}}: CS1 maint: DOI inactive as of October 2023 (link)
  24. ↑ Devi, K.R.; Indra, T.J.; Emiliyamma, K. J. (1996). "On the Fish Collections from Kerala, Deposited in Southern Regional Station, Zoological Survey of India by NRM Stockholm" (PDF). Records of Zoological Survey of India. 95: 3–4. Retrieved 4 May 2022.
  25. ↑ Bijukumar, A.; Philip, Siby; Ali, Anvar; Sushama, S.; Raghavan, Rajeev (26 November 2013). "Fishes of River Bharathapuzha, Kerala, India: diversity, distribution, threats and conservation". Journal of Threatened Taxa. 5 (15): 4979–4993. doi:10.11609/JoTT.o3640.4979-93.
  26. ↑ Easa, P.S.; Shaji, C.P. (1997). "Freshwater fish diversity in Kera a part of the Nilgiri Biosphere Reserve" (PDF). Current Science. 73 (2): 180–182.
  27. 1 2 3 4 Biju, C.R., C.R.; Thomas, R.K.; Ajithkumar, C.R.; George, M.J. (1999). "Occurrence of Tetraodon travancoricus (Hora and Nair) in the Chalakudy, Periyar and Kechery rivers, Kerala". Journal of the Bombay Natural History Society. 96 (1): 161. Retrieved 4 May 2022.
  28. 1 2 Gopi, K.C.; Radhakrishnan, C. (2007). "Waterbird-Mediated Chance-Dispersal of Fishes: A Natural Process of Affecting Range of Distribution and Biogeography of Fishes" (PDF). Records of the Zoological Survey of India. 108 (1): 19–31. doi:10.26515/rzsi/v107/i1/2007/159160. S2CID 201600208. Retrieved 6 May 2022.
  29. 1 2 Dahanukar, Neelesh; Raut, Rupesh; Bhat, Anuradha (22 December 2003). "Distribution, endemism and threat status of freshwater fishes in the Western Ghats of India" (PDF). Journal of Biogeography. 31: 123–136. doi:10.1046/j.0305-0270.2003.01016.x. S2CID 83574801.
  30. ↑ Thomas, K.; George, M.; Biju, C. (April 2002). "Freshwater Fishes of Southern Kerala with Notes on the Distribution of Endemic and Endangered Species". Journal of the Bombay Natural History Society. 99 (1): 47–53. Retrieved 4 May 2022.
  31. ↑ Raghavan, R.; Prasad, G.; Ali, A.P.H.; Pereira, B. (2008). "Fish fauna of Chalakudy River, part of Western Ghats biodiversity hotspot, Kerala, India: patterns of distribution, threats and conservation needs". Biodiversity and Conservation. 17 (13): 3119–3131. doi:10.1007/s10531-007-9293-0. S2CID 7563806.
  32. ↑ Kurup, B.M.; Manojkumar, T.G. (2010). "Central Marine Fisheries Research Institute". Indian Journal of Fisheries. India: Central Marine Fisheries Research Institute. 57 (1): 81–85. ISSN 0970-6011.
  33. 1 2 3 4 Renjithkumar, C.R.; Roshni, K.; Ranjeet, K. (24 September 2020). "Feeding ecology of the endemic freshwater puffer fish Carinotetradon travancoricus (Hora & Nair, 1941) in Western Ghats hotspot, India". International Journal of Aquatic Biology. 8 (5): 300–310. doi:10.22034/ijab.v8i5.922.
  34. ↑ Schäfer, Frank (20 November 2020). "Carinotetraodon travancoricus". www.aquariumglaser.de. Aquarium Glaser GmbH. Archived from the original on 14 October 2023. Retrieved 14 October 2023.
  35. ↑ Monks, Neale (December 2007). "In Search of the Peaceful Puffer". tfhmagazine.com. TFH Magazine. Retrieved 6 May 2022.
  36. ↑ Pagnussat, Natália; Piato, Angelo L.; Schaefer, Isabel C.; Blank, Martina; Tamborski, Angélica R.; Guerim, Laura D.; Bonan, Carla D.; Vianna, Mônica R.M.; Lara, Diogo R. (September 2013). "One for All and All for One: The Importance of Shoaling on Behavioral and Stress Responses in Zebrafish". Zebrafish. 10 (3): 338–342. doi:10.1089/zeb.2013.0867. PMID 23802189.
  37. ↑ Coral fish stress out if separated from 'shoal-mates'. Manila Bulletin Publishing Corp. 22 September 2016. Retrieved 13 May 2022.
  38. 1 2 Anupama, K.M.; Hari Sankar, H.S.; Rithin Raj, M.; Harikrishnan, M. (July 2019). "Reproductive Biology of Malabar Pufferfish Carinotetraodon travancoricus (Tetraodontidae)". Journal of Ichthyology. 59 (4): 545–554. doi:10.1134/S0032945219040027. ISSN 0032-9452. S2CID 201714471. Retrieved 6 May 2022.
  39. 1 2 Ralph, Chris (2003). Practical Fishkeeping: Pufferfish, p. 61. ISBN 1-86054-233-6
  40. ↑ Ponniah, A.G.; Gopalakrishnan, A. (2000). Endemic fish diversity of Western Ghats (PDF). Lucknow, India: National Bureau of Fish Genetic Resources. pp. 13–32. ISBN 81-901014-2-0. Retrieved 5 May 2022.
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