Spotted Green Pufferfish 🐡Tetraodon nigroviridis Marion de Procé, 1822

Introduction

The pufferfish, also known as the blowfish, bubblefish, swellfish, toadfish, globefish, toadies, honey toads, sugar toads and sea squab, belongs to the Tetraodontidae family which consists of 190 pufferfish species in 26 genera.[1] Despite its adorable look when it puffs up into a ball-like shape, pufferfishes are believed to be the second most poisonous vertebrate in the world.[2] In Singapore, a total of ten different species of pufferfish have been recorded.[3]


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Figure 1: The spotted green pufferfish (Tetraodon nigroviridis) has bulging eyes and small mouth. How adorable! (Source: thepufferforum.com.)

Name

Scientific name: Tetraodon nigroviridis Marion de Procé, 1822Common name: Spotted green pufferfish (墨绿凹鼻豚)

Etymology

Tetraodon: Greek, tetra = four + Greek, odous = teeth[5]
nigroviridis: Latin, niger = black (black spots) + Latin, viridis = green (colour of upper body)[21]


Biology

Life Cycle

Mature females lay around 200 eggs, which are attached to a hard, flat submerged surface in shallow water. A parent (usually the male) guards the eggs until they hatch. Adults have been observed tending schools of juveniles.[6]


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Figure 2: Larvae of Spotted Green Pufferfish. (Source: University of Florida©. Permission pending.)


Diet

The pufferfish is a predatory fish. It uses its small mouth, which resembles a parrot’s beak to suck its prey into it before crushing them to bits with its large strong teeth. It usually feeds on shrimps, worms, other finfish, benthic algae, crustaceans and mollusks.[7]


Video 1: A spotted green pufferfish is able to attack snails with its strong teeth.
"Green spotted puffer attacking ramshorn snail" by smallyellowdevil by Youtube Channel 20 July 2008.URL: https://www.youtube.com/watch?v=BCGmrCD2wGA (accessed on 21 Nov 2014)

Self Defense Mechanism

Using a combination of fins, the pufferfish is able to attain high maneuverability. As such, it is unable to swim fast – which makes it an easy target for predators.[8] Fortunately, the pufferfish possesses both mechanical and chemical defenses to protect it from predators. When the pufferfish is threatened by a predator, it quickly puffs its body up by two to three times of its normal size, forming a ball-like shape which makes it difficult to handle.

Video 2: Be amazed by how this pufferfish managed to avoid becoming a snack of the otter through its wonderful puffing ability.
"Freaks of Nature: Self Inflating Fish" by National Geographic by Youtube Channel 5 February 2008.URL: https://www.youtube.com/watch?v=xu47OTMsCg8 (accessed on 21 Nov 2014)

How is this possible?
The secret to the pufferfish's amazing ability is attributed to a unique oral valve which is attached to the floor of its mouth. After filling its mouth with water, the pufferfish flexes a large muscle at the base of the oral valve which then catapults forward against the entire front of the mouth, forming a tight seal against the back of the front teeth. This prevents the water from escaping!
At the same time, the flexing action of the large muscle propels water into the fish's esophagus and then its stomach. With every gulp, the stomach of the pufferfish becomes bigger and so does its body! This amazing ability is made possible by the high elasticity of its stomach and skin. Can you imagine how much the stomach has to expand?
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Figure 3. Illustration of pufferfish inflation (Source: Sally J. Bensusen. American Museum of Natural History)

During this process, the small body spines hidden under the skin at the back, sides and belly of the pufferfish protrude outwards. This gives it a spine-chilling appearance which makes it impossible to be swallowed by its predators. Also notice how the spine of the pufferfish bends when its stomach expands!
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Figure 4: The spines of the pufferfish protrude when it inflates. Eek. Who would dare to swallow this?

However, this tactic is only used as the last line of defense, such as when it is actually grabbed by the predator. This is because it is unable to swim well when it is inflated and it becomes helpless.


Tetrodotoxin

More often than not, bright and beautiful colors of animals indicate danger. It is a way of saying ‘Stay away from from me!’ Similarly, the brightly coloured pufferfish contains tetrodotoxin, a type of neurotoxin, which plays a crucial role in protecting it against predators. This toxin makes its muscular tissue and viscera extremely toxic. This toxin is probably the most lethal form in nature, where it is more than 1000 times more potent than cyanide.[9]

Tetrodotoxin in the pufferfish is produced by certain symbiotic bacteria found in their natural environment, which is accumulated from its diet.[10] To humans, the tetrodotoxin is so deadly that just one pufferfish alone can kill 30 adult humans and there is no known antidote. This acts as a defense mechanism for the pufferfish as the toxin makes it unpalatable. A small bite by a predator can mean death!

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Habitat

The spotted green pufferfish can be found in a wide range of salinity. The adults can be found in freshwater streams, rivers and flood plains while the juveniles can be found in brackish water in coastal areas such as mangrove forests.[7] In Singapore, the spotted green pufferfish is seen hovering in the brackish water in Sungei Buloh.[11]

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Figure 5: The spotted green pufferfish can be found in brackish water habitats like this mangrove forest. (Source: Delicia Cheong)


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Distribution

The spotted green pufferfish can be found in coastal freshwater and brackish water habitats in tropical regions (24°C - 28°C) across South and Southeast Asia.[9] It is native to Thailand, Philippines, Malaysia, Vietnam, Cambodia, Myanmar, India, Sri Lanka, Indonesia and Singapore.[12]

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Figure 6: Spotted green pufferfish is native across South and Southeast Asia (Source: Google Maps)


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General Description


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Figure 7: A spotted green pufferfish discovered in Kranji (Adapted from: Ria Tan. Permission granted.)


Size
Adult spotted green pufferfish usually span between 3 to 6 cm but it can reach a maximum of 14 cm.[13] The length of the fish is measured from the tip of its mouth to the posterior end of the last vertebra.


Colour
Like its name suggests, the spotted green pufferfish has a bright green body with black spots of variable sizes and forms which may coalesce or be encircled by lighter rings. The belly is white and the lateral line across the body is mostly indistinct. Its caudal fin has between 1 to 8 dark transverse bands and sometimes its dorsal fin has small dark spots near the base. The other fins are plain. [21]

Morphology
The body of the spotted green pufferfish is oblong and the posterior part is laterally compressed. Its dorsal profile is arched and the highest point is at the middle of the back. Its mouth is terminal, which allows it to feed on other fishes. The nasal organ is a tentacle and at least half of it is divided into two flattened and broadened lobes. The sides of the lobes have a spongy tissue.[21]

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Figure 8: Illustration of Tetraodon nigroviridis Marion de Procé, 1822. ZMA 113.020, neotype, sl 64mm. (Adapted from: Dekkers, 1975)

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Diagnosis

Pufferfish vs Porcupinefish

Pufferfish from the family Tetraodontidae is often confused with the morphologically similar and closely related porcupinefish of family Diodontidae. However, they can be easily distinguished by the spines on their body. The porcupine fish has large external spines unlike the smaller, hidden spines of the pufferfish from family Tetraodontidae. Also, the porcupinefish can be found in both temperate and tropical waters but the pufferfish is mostly found in the tropics.

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Figure 9: The long-spine porcupinefish has large external spines unlike the spotted green pufferfish. (Source: Holmes Palacios)

Spotted Green Pufferfish vs Green Pufferfish

The spotted green pufferfish (Tetraodon nigroviridis Marion de Procé, 1822) is easily mistaken for its close relative, the green pufferfish (Tetraodon fluviatilis (Hamilton, 1822)) due to the spots on their green bodies. However, they can be distinguished by the differences in their spots. Both have spots and blotches of variable sizes on their upper bodies, but on closer look, green pufferfish (T. fluviatilis) can be distinguished by the three large dark patches on its back![7] The spotted green pufferfish can also be better distinguished by its more rounded shape when compared to the T. fluviatilis. However, due to difficulties in defining the two closed related species through morphology alone, DNA analysis is usually used to distinguish the Tetraodon species.[14]

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Figure 10: A - T. nigroviridis (spotted green pufferfish) with small spots ; B - T. fluviatilis (green pufferfish) with three dark patches on the back. (Source: thepufferforum.com and plantedtankworld.com)


Spotted Green Pufferfish vs Spotted Scat

At first glance, the spotted green pufferfish may also be confused with another similar looking fish - the spotted scat (Scatophagus argus) from the the family Scatophagidae. These two species co-exist in brackish mangrove habitats but they play very different ecological roles. Find out why here.
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Figure 11: C - The Spotted Scat have some similarities to the Spotted Green Pufferfish. Can you spot the difference? (Source: www.mundoacuariofilo.org)

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Commercial Importance

Genetic Research

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Figure 12: A researcher feeding commercially bred young spotted green pufferfishes (Source: University of Florida©. Permission pending.)

The spotted green pufferfish is important in comparative genomic research, which involves the studying of our evolutionary history. This is due to its extremely compact genome – it contains the same number of genes as humans but its genome length is only about ten percent of other vertebrates, which is about 340 million base pairs.[17] This makes it a model organism for comparative genomics where human genes can be identified quickly and reliably .


Aquarium Trade

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Figure 13: Spotted green pufferfish was spotted in a pet shop in Singapore. (Source: Joleen Chan)

Unlike some pufferfish species, the spotted green pufferfish is not sold commercially as a delicacy. Instead, it is a popular fish in the live aquarium trade due to its vivid colours.[18] Although it is not bred in captivity for commercial uses due to its high mortality rate, scientific breakthrough has allowed the spotted green pufferfish to be successfully bred in captivity at University of Florida using a new variation of the ovarian lavage technique in February 2009. This will definitely benefit the tropical fish industry and genetic researchers![17]

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Conservation Status

The pufferfishes in Singapore are not listed among the threatened animals. However, like other creatures in their intertidal habitat, they are affected by human activities such as land reclamation projects and water pollution.[11] Currently, there are about 6.59km2 of mangrove forest left in Singapore, which makes up 0.95% of the total land area. Due to increasing demands for land, the spotted green pufferfish may face further habitat loss as mangrove forests continue to be lost to urban development.[22]


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Taxonomy and Phylogeny

Synonym

Arothrom simulans (Cantor, 1849)
Chelonodon nigroviridis (Marion de Procé, 1822)Tetraodon potamophilus Bleeker, 1849Tetraodon simulans Cantor, 1849

Type Information

The holotype of the Tetraodon nigroviridis Marion de Procé, 1822, which was collected and described by Marion de Procé during a trip from France to Manila, Philippines is believed to have been lost in a revolt.[21]

A neotype which is designated by Dekkers in 1975 is now housed in the Institute of Taxonomic Zoology (Zoölogisch Museum), University of Amsterdam, The Netherlands.[21]


Taxonomic Classification

Kingdom: AnimaliaPhylum: ChordataClass: ActinopterygiiOrder: TetraodontiformesFamily: TetraodontidaeGenus: TetraodonSpecies: Tetraodon nigroviridis Marion de Procé, 1822[15]


Phylogenetic Relationship of Tetraodon pufferfish

In the study by Igarashi et al., 2013, the phylogenetic relationship of 17 Tetraodon species were analyzed by sequencing their mitochondrial genes encoding 16S rRNA and cytochrome b.[16] The sequencing results were then used to construct the following molecular phylogenetic tree using the maximum likelihood (ML) method and supermatrix analysis.


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Figure 14: Phylogentic tree of family Tetraodotidae (Adapted from: Igasrashi et al, 2013.© Permission pending.)

Through the phylogenetic tree, we can see that the genus Tetraodon contains pufferfish which do not form a monophyletic group. Instead, they are nested in four different clades in the family in Clade D (shown in yellow). Within the four clades, three distinct groups (Asian freshwater, Asian brackish water and African freshwater groups), which correlated to their habitats, were identified. These three Tetraodon groups form a well-supported cluster (bootstrap probability 100%) with each sister group.

This relationship may be associated with the salinity tolerance of the Tetraodon species which was caused by the the molecular evolution associated with osmotic regulation. Therefore, in the Asian brackish water group*, T. erythrotaenia diverged from the common ancestor first followed by T. biocellatus. Finally, two remaining and very closely-related species formed, namely T. fluviatilis and T. nigroviridis (spotted green pufferfish).


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Did You Know?

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Figure 15: Sashimi style fugu is a popular delicacy in Japan.

Despite the long history of toxic effects, the flesh of some pufferfish species such as the Takifugu radiatus (excluding the spotted green pufferfish) is considered as a delicacy in Japan.[18] Although the toxins are accumulated in its skin, ovaries, intestines and liver, consuming its flesh still comes with some risk.[19] Known as fugu, the delicacy is only prepared by licensed chefs who have undergone years of training. However, one wrong cut may mean the death the consumer. In fact, up to 50 deaths from pufferfish poisoning are reported in Japan annually. This is due to the potent tetrodoxin, which is 1000 times more lethal than cyanide. Due to this reason, the fugu is the only food which the Emperor of Japan is forbidden to eat.

In Singapore, fugu is partially banned and special permits are required to import the flesh while other parts of the fish is forbidden. Unfortunately, accidents are still reported.[20] Symptoms of poisoning include vomiting, diarrhea and paralysis. In severe cases, death can result from respiratory paralysis. Indeed, it is a dish to die for.


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Glossary of Terms

Bootstrap probability: A computer based technique used to assess the accuracy of the statistical estimate.

Holotype: A single physical example (or illustration) of an organism, known to have been used when the species was formally described.

Monophyletic group / clade: A group consisting of an ancestor and all its descendants, a single branch on the tree of life.

Neotype: A specimen later selected to serve as the single type specimen when an original holotype has been lost or destroyed or where the original author never cited a specimen.

Phylogenetic relationship: The relative times in the past that species shared common ancestors. Two species are more closely related to one another than either one is to a third species if, and only if, they share a more recent common ancestor with one another than they do with the third species.

Phylogenetic tree: A branching diagram showing the inferred evolutionary relationships of various biological species or their phylogeny. Each branching shows successive events of speciation, in which one species gives rise to two.

Terminal: A protrusible mouth design which helps the fish to feed on other fish efficiently.


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References

[1] Nelson, J. S., 1994. Family Tetraodontidae - Puffers. FishBase. URL: http://www.fishbase.org/Summary/FamilySummary.php?ID=448 (Accessed on 1 Nov 2014)
[2] Puffer Fish (Tetraodontidae). A-Z Animals. URL: http://a-z-animals.com/animals/puffer-fish (Accessed on 1 Nov 2014)

[3] Ria, T. 2008. Pufferfishes (Tetraodontidaes) on the Shores of Singapore. WildFactsheets, 13 Dec 2008. URL: http://www.wildsingapore.com/wildfacts/vertebrates/fish/tetraodontidae/tetraodontidae.htm (Accessed on 1 Nov 2014)

[4] Tetraodon nigroviridis Marion de Procé, 1822 – Checklist View. GBIF. URL: http://www.gbif.org/species/5213566 (Accessed on 1 Nov 2014)

[5] Romero, P., 2002. An etymological dictionary of taxonomy. Madrid. unpublished.

[6] Pethiyagoda, R., 1991. Freshwater fishes of Sri Lanka. The Wildlife Heritage Trust of Sri Lanka, Colombo. 362 p.

[7] Rainboth, W.J,. 1996. Fishes of the Cambodian Mekong. FAO Species Identification Field Guide for Fishery Purposes. FAO, Rome, 265 p.

[8] Frederick, L. C, 2001. Puffernet: Anatomy and Physiology. URL: http://puffernet.tripod.com/ap.html (Accessed on 1 Nov 2014)

[9] Tetraodon nigroviridis (Green Spotted Puffer) – Seriously Fish. URL: http://www.seriouslyfish.com/species/tetraodon-nigroviridis (Accessed on 1 Nov 2014)

[10] Tetrodoxin: The Neurotoxin. University of Maryland. URL: http://www.life.umd.edu/grad/mlfsc/zctsim/Tetrodo.html (Accessed on 1 Nov 2014)

[11] Ria, T. 2008. Spotted Green Pufferfishes (Tetraodon nigroviridis) on the Shores of Singapore. WildFactsheets, 13 Dec 2008. URL: http://www.wildsingapore.com/wildfacts/vertebrates/fish/tetraodontidae/nigroviridis.htm (Accessed on 1 Nov 2014)

[12] Froese, R. and D. Pauly (eds). 2012. FishBase. World Wide Web electronic publication. URL: http://www.fishbase.org (Accessed on 1 Nov 2014)

[13] Talwar, P. K. and A. G. Jhingran. 1992. Inland fishes of India and adjacent countries. Volume 2. A. A. Balkema, Rotterdam.

[14] Tetraodon nigroviridis. Genoscope - Centre National de Séquençage. URL: http://www.genoscope.cns.fr/spip/spip.php?lang=en (Accessed on 1 Nov 2014)

[15] Tetraodon nigroviridis. ITIS Standard Report Page. URL: http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=646446. (Accessed on 1 Nov 2014)

[16] Igarashi, Y., H. Doi, Y. Yamanoue, S. Kinoshita, T. Ishibashi, H. Ushio, S. Asakawa, M. Nishida, S. Watabe. 2013. Molecular phylogenetic relationship of Tetraodon pufferfish based on mitochondrial DNA analysis. The Japanese Society of Fisheries Science. 79:243–250


[17] Nordlie, T., 2009. UF experts breed puffer fish in captivity; pet trade and genetics research could benefit. University of Florida News. URL: http://news.ufl.edu/archive/2009/02/uf-experts-breed-puffer-fish-in-captivity-pet-trade-and-genetics-research-could-benefit.html (Accessed on 1 Nov 2014)

[18] Foreign Fisheries Developments. "Japan's "Fugu" or Puffer Fish Market" Marine Fisheries Review. URL: http://spo.nmfs.noaa.gov/mfr511/mfr51112.pdf (Accessed on 1 Nov 2014)

[19] Yong, Y. S., L. S. Quek, E. K. Lim, and A. Ngo. 2013. A Case Report of Puffer Fish Poisoning in Singapore. Case Reports in Medicine. vol. 2013, Article ID 206971, 4 pages, 2013.

[20] Dekkers, W. J., 1975. Review of the Asiatic freshwater puffers of the genus Tetraodon Linnaeus, 1758 (Pisces, Tetraodontiformes, Tetraodontidae). Bijdragen tot de Dierkunde. 45(1), 123

[21] Nijssen, H., L. van Tuijl, J. H. Isbrücker, 1993. Revised catalogue of the type specimens of recent fishes in the Institute of Taxonomic Zoology (Zoölogisch Museum), University of Amsterdam, The Netherlands. Bulletin Zoologisch Museum. 13(18), 235

[22] Yee, A. T. K., W. F. Ang, S. Teo, S. C. Liew and H. T. W. Tan, 2010. The present extent of mangrove forests in Singapore. Nature in Singapore 2010. 3: 139–145