Cetoscarus bicolor

Cetoscarus bicolor
Terminal phase above, initial phase below
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Labriformes
Family:	Scaridae
Genus:	Cetoscarus
Species:	C. bicolor
Binomial name
Cetoscarus bicolor (Rüppell, 1829)
Synonyms[2]
Scarus bicolor Rüppell, 1829 Bolbometopon bicolor (Rüppell, 1829) Chlorurus bicolor (Rüppell, 1829) Scarus pulchellus Rüppell, 1835 Callyodon pulchellus (Rüppell, 1835) Cetoscarus pulchellus (Rüppell, 1835) Chlorurus pulchellus (Rüppell, 1835) Pseudoscarus nigripinnis Günther, 1867

Cetoscarus bicolor, also known as the bicolour parrotfish or bumphead parrotfish, is a species of fish belonging to the family Scaridae. It is found only in the Red Sea. Being from the Scaridae family of huge, vividly colored fish, which is well known as a main contributor of marine ecosystems, especially coral reefs by maintaining them.

Visualization of where Cetoscarus bicolor is found.

(Bray, D.J. 2017)

It is among the largest parrotfishes, growing to a standard length of up to 50 cm (20 in). As in many of its relatives, it is a sequential hermaphrodite, starting as female (known as the initial phase) and then changing to male (the terminal phase). The initial phase is dark brown with a large cream patch on the upper part of the body. The terminal phase is very colorful, overall green with pink spotting to the body and edging to the fins. Juveniles are white with a black spot on the dorsal fin and an orange band through the eye. It is hence different from the adult phase, where they lose the black dot on their dorsal fin and as they mature their color shifts to a bright blue body, with a spotted face, and some pink/yellow highlights around the scales. Because of their pigmentation, juvenile Baltas are known as "black tooth" because they have dark bands and patches that distinguish them from their mature counterparts (Friedlander et al., 2019).Cetoscarus bicolor has a distinct color division between the two phases in its life cycle, which defines its appearance.

Juvenile Cetoscarus bicolor, showing its characteristic white body with black dorsal fin spot and orange eye band.

(MarineFishEZ)

The development of sexual dimorphism is a sign of sexual maturity. Typically dark brown, juveniles and subadults have a large white patch on the dorsal region above the dorsal fin that will soon appear. When reaching the terminal phase, the body is sporadically studded with pink, the fins have bright pink edges, and the overall coloration turns bright green (Randall, 2021). Males in the terminal phase are generally noticeable and obvious due to this coloring.

Adult male Cetoscarus bicolor, showing the vibrant green coloration typical of the terminal male phase.

(Marshall Islands, 1840)

During its lifetime, this fish changes sex twice and very large females change sex to become brightly coloured males. This fish is a sequential hermaphrodite. Cetoscarus bicolor undergoes a transition from female to male in every individual. Molecular data and external morphology investigations have demonstrated that this process, together with sexual size and color differentiation, is typical of the species. It is clear that Cetoscarus bicolor belongs to the same family as Cetoscarus Ocellatus, but research using DNA information and morphological variations distinguishes the two species. Highlighting Cetoscarus bicolor's uniqueness among its genus members, Cetoscarus Ocellatus differs from Cetoscarus bicolor in color, with having a less vivid coloring.(Choat et al., 2012; Randall, 2021).

Illustration of gender transition in Cetoscarus bicolor

(Sadovy de Mitcheson & Liu, 2020)

As in other parrotfish species, males are territorial. They are born female in a female-dominated civilization and can only change their gender as they mature, usually as they get older. This shift is a result of social and environmental factors. When there isn't a male in the group, activation takes place. Cetoscarus bicolor is sexually mature at around three years of age, and the size distribution for a given population tends to show that the largest fish are male due to this lot of alternative gonochorism (Choat & Robertson, 2020). This system has significant biological potency in controlling breeding populations because it has a flexible breeding structure that can cope with population changes. This is especially beneficial in reef environments since population numbers and sex differentiation can change due to typical disturbances and predation risks (Sadovy et al., 2020).

While this species is restricted to the Red Sea, it is related to the spotted parrotfish (Cetoscarus ocellatus), which is also sometimes called the bicolour parrotfish.These species were formally classified as one, the only in the genus Cetoscarus, but there are major molecular and morphological differences between the two. C. bicolor is associated with coral reefs. It usually can be found in lagoons and seaward reefs at depths between 1 and 30 m (3 ft 3 in and 98 ft 5 in). Small juveniles are usually found among dense coral and in algae-rich habitats. However, individuals have been found down to 40 meters, and they dive into the large coral systems in their geographical distribution (Samoim et al., 2020). These areas offer them all the required conditions for feeding and surviving; there are lots of algae to eat and coral chunks to stay and reproduce.

A coral reef habitat in the Red Sea, where Cetoscarus bicolor commonly resides.

( Bellwood & Hoey, 2019)

Cetoscarus bicolor is a species with space use abilities that differ according to the life cycle stage the fish is at. For example, juvenile parrotfish are found in the thick coral sections or areas of vegetation, where they can access food and avoid predation. Juveniles are commonly associated with coral gardens and lagoons since their coloration is white, with a black spot on the dorsal fin and an orange stripe over the eye (Westneat & Alfaro, 2021). Now adults prefer the outside of the coral reefs or open reef areas, which they demarcate as their feeding grounds. These territories are the coral and rocky ground suitable for removing algae and biofilm from the reef using body scrapes, which is part of their diet (Bellwood & Hoey, 2019).

It is hard to find information on the populations of this species but Pauly, and Froese indicate that there are healthy numbers in the Red Sea stretching region. However, the authors detected fluctuations in population densities. They called for more studies to define more precise rates of their modern population and their abilities to withstand certain kinds of stress in their surroundings (Froese & Pauly, 2019). It is expected that with climate change and continued human interference, the health of the reefs on which Cetoscarus bicolor rely on will degrade over time. Ensuring the stability of the species and the overall balance of such fragile ecosystems as the Red Sea habitats means the necessity of the further continuation of the conservation programs directed at protecting the reefs.

As for their diet, the Gulf of Mexico's Cetoscarus bicolor mainly feeds on algae, and the species is known to scrape off the rocks and corals using the bottom part of its beak-like dental plates. Cetoscarus bicolor feeds on this algae which could otherwise be a thick layer on coral reefs, overall denying light and photosynthesis to the coral symbiont, as stated by Green and Bellwood in 2019’’. Parrotfish species are usually considered reef 'gardens' since they help maintain algae that threatens to overgrow the reefs. They play a role in establishing grounds on which corals can grow, creating room for reefs to support biological diversity. Furthermore, they feed to form fine sand through bioerosion because they graze on rock, and corals break them down. While feeding on coral and rocks, it chews the rock so hard on these materials in digesting it and expelling it as sand, this process is known as sediment production. The process discussed above leads to the formation of sediment that is then expelled like sand to enhance sand formation in the reef environment and marine life in general (Randall, 2021).Overall, Cetoscarus bicolor enhances coral health and, while not depicted directly, influences changes in the reef framework (Choat et al., 2012). Together, the ability of Cetoscarus bicolor to control algae and generate sediment makes this species central to coral reef ecosystems, contributing to the overall biological and resilience of the coral itself.

Since Cetoscarus bicolor is not listed as endangered, it is categorized as a low concern on the IUCN Red List (IUCN, 2021). Though it is completely symbiotic with coral reef ecosystems. Because of its dependence on them, the species is at risk as a result of additional environmental stressors brought on by climate change. One of the major effects of global warming is coral bleaching, particularly for Cetoscarus bicolor, whose habitat or food source is severely degraded (Anthony et al., 2020). This parrotfish's food supplies are coral-dependent algae resources, which die during bleaching. This causes catastrophic coral death and the loss of reef architectural complexity, which is essential for many marine creatures, including this parrotfish.

Bleached coral reef affected by rising sea temperatures, one of the main threats to Cetoscarus bicolor’s habitat.

(NBC News, 2020, February 19)

In addition to climate change impacts, Cetoscarus bicolor faces other risks, such as pollution, overfishing, and coastal development. However, pollutants such as farm runoff contain higher nutrients, which can further fuel the coral-harming algae and water quality, further intensifying pressure on the coral systems (Hughes et al., 2021).

Given these threats, continuous effort must be put in place to protect coral reefs and ensure that Cetoscarus bicolor and all other species that depend on the coral can continue to exist in the future. Some of the current strategies include measures aimed at cutting down greenhouse gas emissions, combating climate change, and other pointed measures involved in controlling pollutant discharges and uncontrolled fishing activities. Current and future perspectives of climate change are being addressed by organizations like the IUCN or local governments, and they are paying attention to the ecosystem's ability to adapt with change; efforts are being made to strengthen coral reefs against climate change (Mumby et al., 2020; Froese & Pauly, 2019). In the case that we follow these efforts, the threats above can slowly diminish,  if not it can cause a substantial decrease in the Cetoscarus bicolor population and affecting the diverse coral species and their ecosystems.

Wikimedia Commons has media related to Cetoscarus bicolor.

Wikispecies has information related to Cetoscarus bicolor.

Anthony, K. R. N., et al. 2020. Coral bleaching and climate change: Patterns and mechanisms. Marine Ecology Progress Series 654:1–16.

• Bellwood, D. R., and A. S. Hoey. 2019. Parrotfish functional morphology and ecology. Annual Review of Marine Science 11:269–292.
• Bray, D. J. 2017. Cetoscarus ocellatus. Fishes of Australia. Available: https://fishesofaustralia.net.au/home/species/390. (November 8, 2024).
• Encyclopedia of Life. Bicolor Parrotfish - Cetoscarus bicolor - Details.
• Randall, J. E. 2005. Reef and Shore Fishes of the South Pacific. University of Hawaii Press, Honolulu.
• Choat, J. H., B. Russell, K. D. Clements, L. A. Rocha, R. Myers, M. E. Lazuardi, A. Muljadi, S. Pardede, and P. Rahardjo. 2012. Cetoscarus bicolor. IUCN Red List of Threatened Species 2012
• .T190690A17793737. Available: https://doi.org/10.2305/IUCN.UK.2012.RLTS.T190690A17793737.en. (November 20, 2021).
• Froese, R., and D. Pauly, editors. 2019. Cetoscarus bicolor. FishBase. March 2019 version.
• Hughes, T. P., et al. 2021. Coral reefs in the Anthropocene. Nature 593:39–49.
• IUCN. 2021. Cetoscarus bicolor. IUCN Red List of Threatened Species e.T190690A17793737.
• Mumby, P. J., et al. 2020. Management of coral reef resilience. Current Biology 30(19) –R1099.
• Mumby, P. J., and A. R. Harborne. 2021. Coral reefs under threat. Marine Pollution Bulletin 170:112742.
• Randall, J. E. 2021. Reef and Shore Fishes of the Red Sea. University of Hawaii Press, Honolulu.
• Sadovy de Mitcheson, Y., and M. Liu. 2020. Endangered status of reef fish. Science Advances 6(8)

• Photos of Cetoscarus bicolor on Sealife Collection