Pinktail triggerfish

Pinktail triggerfish
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Tetraodontiformes
Family:	Balistidae
Genus:	Melichthys
Species:	M. vidua
Binomial name
Melichthys vidua (J. Richardson, 1845)
Synonyms
Balistes nycteris Balistes vidua Pachynathus nycteris Oncobalistes erythropterus

The pinktail triggerfish (Melichthys vidua) is a species of triggerfish native to the Indo-Pacific. It is very dark green (often appears almost black) with translucent white anal and second dorsal fins, and a pink caudal fin from which it gets its name. They are found exclusively around shallow reefs where they live their whole lives. Pinktail triggerfish are also not uncommon in the aquarium trade.^[1][2]

Description

Pinktail Triggerfish have a football-shaped, compressiform body, which can grow up to 40 centimeters (16 in) in length. Like all triggerfish species, their first dorsal fin is composed of three spines that can be “triggered” up and down to lock the fish inside crevices to thwart predators. They also have great control of their other fins, including symmetrical anal and second dorsal fins that undulate left and right and serve as the fishes primary method of locomotion. Their pink caudal fin can also be splayed from a squared to a wide rounded, almost truncated shape for different burst movement options. Their pectoral fins are rather unremarkable apart from being a much brighter green, and their pelvic fins are nearly invisible, being quietly tucked underneath their ventral side. Pinktail triggerfish possess a small terminal mouth, as well as small eyes due to their preference for bright, shallow reefs. Their body is covered in tough cycloid scales, and their opercula (gill flaps) are not visible but are hidden underneath their skin, and instead have a single gill slit.^[3]

Cycloid scales of Melichthys vidua

Distribution

The pinktail triggerfish is found throughout the Indian and Pacific oceans. The greatest density of their populations occur around Indonesia and Oceania, but can be found as far west as the African east coast all the way to the western coast of Panama, and occur as far north as southern Japan. They live exclusively in shallow coral reefs, preferring reef slope edges near the surface. This is likely due to its planktivore diet, where currents from more open ocean can provide a constant renewal of plankton. Adults prefer areas with large corals, while juveniles prefer rockier parts of the reef, which provides better cover against predators for smaller, weaker fish.^[4]

Ecology

Pinktail triggerfish are planktivores, feeding on microalgae especially. This is somewhat unique among triggerfish, as a majority of species consume hard-shelled invertebrates like crabs and urchins with their crushing teeth. However, pinktail triggerfish are also egg predators (ovivores), and are known to follow spawning fish individually and in pairs to consume the eggs of other reef fish, including Aulostomus chinensis, Parupeneus bifasciatum, Chlorurus sordidus, Acanthurus nigroris, Bothus mancus and Ostracion meleagris. The preference for these fish species was determined to be due to the fact that they spawned in pairs, which correlated to larger egg sizes.^[5]

To avoid reef predators like sharks and eels, pinktail triggerfish can activate their trigger-like dorsal spines to lock them inside rocks until the threat has passed. In addition, their large spines, tough scales, and general thick compressiform body plan make them more difficult for predators to grab onto and swallow. They also have to deal with aquatic parasites like trematodes, a type of flatworm, which must complete part of their life-cycle inside of a fish host. In particular, the species Lepocreadium clavatum and Opisthogonoporis vitellosus were both described from specimens inhabiting pinktail triggerfish.^[6]

Life history

Pinktail triggerfish are known to breed in pairs. They are also not sexually dimorphic: male and female triggerfish are identical to each other. While not much is known about breeding and spawning habits specific to pinktail triggerfish, the common sexual behaviors of other triggerfish species can be extrapolated onto them. Triggerfish build nests for their eggs, and males become extremely defensive of their territory, even toward fishes and other animals many times larger than they are. Aquarium owners have reported that pinktail triggerfish act less territorial than other species of triggerfish, however.^[7] The nest triggerfish build is usually dug out of sand on the ocean floor, but can also be made from existing space in rocky reefs. When spawning, both the male and female rub their abdomens on the bottom of the nest to release and fertilize the eggs. Once the eggs have been fertilized, the female tends to the eggs by constantly moving them to provide a constant source of oxygen, while the male further patrols the territory from other egg predators.^[8] After the eggs hatch, the baby fish then swim off on their own to safer parts of the reef with more cover.^[9]

Human interference

The pinktail triggerfish is listed as a Least-concern species by the International Union for Conservation (IUCN), due to their large population, widespread range, and relative indifference from humans.^[10] This fish is not edible due to ciguatoxins, which are produced by tropical algae and eaten by herbivorous reef fish.^[11] Pinktail triggerfish were also found to contain high amounts of palytoxin, also originating from microalgae.^[12] There are however a few threats that could perhaps raise this species listing. The continued death of corals and degradation of reef habitats due to climate change and ocean acidification could cause large declines in this species population, as will all other species that are ecologically dependent on reefs. Pinktail triggerfish are also sought after in the saltwater aquarium trade, and all individuals must be wild-caught. However, so far there exists only one fishery in Micronesia that harvests them, and they report that they follow sustainable fishing practices. Therefore, unless a huge market suddenly develops, this will not pose a serious issue to the species’ population survival.^[13]

References

1. "Pinktail Triggerfish Are Fish That's a Joy to Own". The Spruce.
2. [1] Saltwater Aquariums: Pinktail Triggerfish Profile
3. Randall, J.E. (1971). "The Nominal Triggerfishes (Balistidae) Pachynathus nycteris and Oncobalistes erythropterus, Junior Synonyms of Melichthys vidua". Copeia. 3 (462): 462–469. doi:10.2307/1442442. JSTOR 1442442.
4. Bean, K.; Jones, G.; Caley, M. (2002). "Relationships among distribution, abundance and microhabitat specialisation in a guild of coral reef triggerfish (family Balistidae)". Marine Ecology Progress Series. 233: 263–272. Bibcode:2002MEPS..233..263B. doi:10.3354/meps233263.
5. Sancho, G.; Peterson, C.; Lobel, P. (2000). "Predator-prey relations at a spawning aggregation site of coral reef fishes". Marine Ecology Progress Series. 203: 275–288. Bibcode:2000MEPS..203..275S. doi:10.3354/meps203275.
6. Pritchard, M. H. (1963). "Studies on Digenetic Trematodes of Hawaiian Fishes, Primarily Families Lepocreadiidae and Zoogonidae". The Journal of Parasitology. 49 (4): 578–587. doi:10.2307/3275763. JSTOR 3275763. PMID 14050234.
7. Michael, S.W. (2001). Marine fishes : 500+ essential-to-know aquarium species. Charlotte, Vt.: T.F.H. Publications.
8. Gladstone, W. (1994). "Lek-like spawning, parental care and mating periodicity of the triggerfish Pseudobalistes flavimarginatus (Balistidae)". Environmental Biology of Fishes. 39 (3): 249–257. Bibcode:1994EnvBF..39..249G. doi:10.1007/bf00005127.
9. Lobel, P. S.; Johannes, R. E. (1980). "Nesting, eggs and larvae of triggerfishes (Balistidae)". Environmental Biology of Fishes. 5 (3): 251–252. Bibcode:1980EnvBF...5..251L. doi:10.1007/bf00005359.
10. Zhang, K.; Zhang, J.; Shi, D.; Chen, Z. (2021). "Assessment of Coral Reef Fish Stocks From the Nansha Islands, South China Sea, Using Length-Based Bayesian Biomass Estimation". Frontiers in Marine Science. 7 610707. Bibcode:2021FrMaS...710707Z. doi:10.3389/fmars.2020.610707.
11. Isbister, G. K.; Kiernan, M. K. (2005). "Neurotoxic marine poisoning". The Lancet Neurology. 4 (4): 219–228. doi:10.1016/s1474-4422(05)70041-7. PMID 15778101.
12. Fukui, M.; Murata, M.; Inoue, A.; Gawel, M; Yasumoto, Takeshi (1987). "Occurrence of palytoxin in the trigger fish Melichtys vidua". Toxicon. 25 (10): 1121–1124. Bibcode:1987Txcn...25.1121F. doi:10.1016/0041-0101(87)90269-8.
13. Nahacky, T.; Wabnitz, C. (2014). "Aquarium fish black list and recommendations for the management of aquarium fish collection in French Polynesia" (PDF). Spc.int.

External links

• Fishes of Australia : Melichthys vidua
• Photos of Pinktail triggerfish in the Sealife Collection