Coral reef fish diversity

Every species tells a different story. And every species counts in the diverse coral reef ecosystem. Coral reef fishes are not interchangeable: each species has its own biology, behaviour, habitat needs and ecological role. Some help maintain the balance between algae and corals, some structure social and reproductive interactions, and others contribute to the food web in ways that are still poorly understood. Trade affects species differently, depending on their abundance, range size, reproductive biology and the way they are collected.

This is why species-level monitoring is essential.

~ ~~ 🐠 ~~ ~

More than colourful aquarium fishes

Coral reefs are home to more than 4,000 fish species, making them one of the richest vertebrate communities on Earth. Around 3,000 species are currently known to be collected for the marine aquarium trade. Although these fishes are often grouped together under the term marine ornamental fishes, they differ enormously in their ecology, distribution, behaviour and vulnerability to human activities. [1][2]

Each year, an estimated 15–30 million coral reef fishes are traded internationally. Yet surprisingly little is known about many of these species. Between 2014 and 2021, almost 30% of coral reef fishes imported into the European Union were not recorded at species level, making it impossible to determine precisely which species were traded or assess their conservation status. [2][3]

Knowledge gaps remain significant in conservation. Recent IUCN Red List efforts have greatly improved coverage for marine ornamental fishes, and most species in the AC33 Inf. 5 dataset now have a published assessment. However, important gaps remain: some species are still listed as Not Evaluated or Data Deficient, and many assessments are more than ten years old and therefore require updating. The absence of an assessment, or a Data Deficient classification, should therefore never be interpreted as evidence that a species is not threatened. [2][4][5]

The families most frequently represented in international trade are damselfishes (Pomacentridae) and wrasses (Labridae), followed by angelfishes (Pomacanthidae), surgeonfishes (Acanthuridae), gobies (Gobiidae) and butterflyfishes (Chaetodontidae). [2][6]

~ ~~ 🐠 ~~ ~

Did you know?

• Coral reefs are home to more than 4,000 fish species. [1]
• Around 3,000 species are collected for the marine aquarium trade. [2]
• Between 15 and 30 million fishes are traded internationally every year. [2][6]
• 30% of EU imports were not identified to species level. [2]
• Many coral reef fish species still lack up-to-date conservation assessments. [4][5]

~ ~~ 🐠 ~~ ~

Why some species are more vulnerable than others

Coral reef fishes are often discussed as if they formed one uniform group. In reality, each species has its own biology, ecological role and conservation challenges.

Some species occur only in a tiny geographical area. Others are essential for maintaining healthy coral reefs. Some are especially attractive to the aquarium trade, while others are difficult or impossible to breed in captivity. These differences determine how vulnerable each species may be to collection and international trade.

The following examples illustrate why understanding species biology is essential for effective conservation.

~ ~~ 🐠 ~~ ~

Endemic species

Banggai cardinalfish (Pterapogon kauderni)

The Banggai cardinalfish has become one of the best-known examples of the conservation challenges associated with the marine aquarium trade.

Unlike most coral reef fishes, it occurs naturally only within a tiny archipelago off eastern Central Sulawesi, Indonesia, covering approximately 23 km². Because the species has no pelagic larval stage, populations remain genetically isolated and recover only slowly after depletion. [7]

The Banggai cardinalfish also has unusual reproductive biology. Males brood approximately 50–60 eggs inside their mouths until fully developed juveniles are released. This remarkable parental care comes at the cost of low reproductive output, making the species particularly vulnerable to overharvesting. [7]

After more than 90% of some populations had been removed for the aquarium trade, the species was classified as Endangered on the IUCN Red List in 2007. Although captive breeding is now possible, wild collection remains economically attractive and continues today. [7][8]

Our research has focused extensively on this species and its international trade. [9]

Despite two proposals to regulate international trade through CITES, submitted by the United States in 2007 and by the European Union in 2016, neither proposal was adopted, leaving the species without international trade regulation. [10][11]

Why is this species particularly vulnerable?

• Extremely restricted distribution
• No larval dispersal
• Low reproductive output
• High demand in the aquarium trade
• Continued wild collection despite captive breeding

~ ~~ 🐠 ~~ ~

Keystone species

Common cleaner wrasse (Labroides dimidiatus)

Some coral reef fishes are important not because they are rare, but because of the ecological services they provide.

The common cleaner wrasse removes parasites and dead tissue from hundreds of other reef fishes, including sharks and rays. These cleaning interactions help maintain healthy reef communities.

Experimental studies have shown that removing cleaner wrasses from coral reefs leads to a rapid decline in fish diversity within only a few months. [12][13][14]

This species performs poorly in captivity and is therefore not recommended even by experienced aquarists. [15]

Why is this species important?

• Maintains reef fish health
• Supports biodiversity
• Difficult to maintain in captivity
• Plays a unique ecological role

~ ~~ 🐠 ~~ ~

Popular aquarium species

Blue tang (Paracanthurus hepatus)

Following the release of Disney’s Finding Nemo and later Finding Dory, the blue tang became one of the world’s best-known coral reef fishes.

Its popularity greatly increased demand within the aquarium trade.

Although captive breeding has now been achieved, wild collection continues because producing juveniles in captivity remains technically difficult and relatively expensive. Fish marketed as “farmed” may also include wild-caught juveniles grown to market size rather than animals bred entirely in captivity. [16][17]

~ ~~ 🐠 ~~ ~

When size matters

Juvenile collection

Bicolour parrotfish (Cetoscarus bicolor)

Many colourful reef fishes enter the trade as juveniles.

Removing excessive numbers of young fish can alter the natural age structure of populations and reduce the number of individuals that survive to reproduce. This is particularly important for species whose survival, reproductive output or social structure depends on age and size. [18]

~ ~~ 🐠 ~~ ~

When sex matters

Mandarin fish (Synchiropus splendidus)

In some species, collectors preferentially target males because of their brighter colours.

In the mandarinfish Synchiropus splendidus, selective harvest for the aquarium trade appears to affect population sex ratios in parts of the species’ range. Leung et al. (2020) compared heavily fished sites in Bohol, Philippines, with an unexploited site in Palau and found highly skewed male ratios, with far fewer males in several harvested populations. This pattern is consistent with sex-selective collection, as males are preferred in the trade because of their enlarged first dorsal fins. [19]

~ ~~ 🐠 ~~ ~

The world’s most traded coral reef fish

Blue-green damselfish (Chromis viridis)

In the United States alone, almost one million individuals are imported annually. [6]

In parts of Indonesia and the Philippines, illegal cyanide fishing continues despite decades of prohibition, harming corals, non-target organisms and sometimes even the fishermen themselves. [20][21]

~ ~~ 🐠 ~~ ~

Science in Action

Identifying species that may require closer attention

One of the major challenges in coral reef fish conservation is determining which species may be most vulnerable to international trade.

Our research developed the first evidence-based watchlists by combining trade volume, trends in trade, conservation status and biological vulnerability. [22]

The original Watchlist identified 17 species that may warrant closer monitoring.

In our 2024 study, we refined this approach using eight years of EU trade data from 2014 to 2021, producing both an updated Watchlist and a WatchlistPLUS, incorporating statistical trend analyses to improve species prioritisation. [2]

~ ~~ 🐠 ~~ ~

Captive breeding

Unlike freshwater ornamental fishes, captive breeding remains possible for only a small proportion of coral reef fish species.

Although almost 3,000 species are traded, only around 25 species are currently bred commercially, while breeding techniques for approximately 340 species remain under development. [2][23]

Marine fish larvae have extremely specialised nutritional requirements, making captive breeding technically difficult and often more expensive than collecting fish from the wild. [23][24]

The story of anemonefishes illustrates both the opportunities and limitations of captive breeding. Although they can now be bred successfully, global production still cannot satisfy demand, and wild collection continues in many parts of the world. [25]

~ ~~ 🐠 ~~ ~

Every species tells a different story

Coral reef fishes cannot be managed as a single group. Each species has its own ecology, life history and conservation challenges.

Understanding these differences is essential if international trade is to be monitored effectively and conservation decisions are to be based on sound scientific evidence rather than assumptions.

~ ~~ 🐠 ~~ ~

References

[1] Nelson, J.S., Grande, T.C. & Wilson, M.V.H. (2016). Fishes of the World (5th edition). Wiley. https://onlinelibrary.wiley.com/doi/book/10.1002/9781119174844

[2] Biondo, M.V., Burki, R.P., Aguayo, F. & Calado, R. (2024). An Updated Review of the Marine Ornamental Fish Trade in the European Union. Animals, 14, 1761. https://doi.org/10.3390/ani14121761

[3] Biondo, M.V. & Calado, R. (2025). Enhancing Wildlife Trade Monitoring in the European Union—No Need to Reinvent the Wheel. Ecology and Evolution, 15(9), e72090. https://doi.org/10.1002/ece3.72090

[4] International Union for Conservation of Nature. The IUCN Red List of Threatened Species. https://www.iucnredlist.org

[5] Biondo, M.V. & Burki, R.P. (2020). A Systematic Review of the Ornamental Fish Trade with Emphasis on Coral Reef Fishes—An Impossible Task. Animals, 10, 2014. https://www.mdpi.com/2076-2615/10/11/2014

[6] Rhyne, A.L., Tlusty, M.F., Schofield, P.J., Kaufman, L., Morris, J.A. & Bruckner, A.W. (2012). Revealing the Appetite of the Marine Aquarium Fish Trade: The Volume and Biodiversity of Fish Imported into the United States. PLoS ONE, 7(5), e35808. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0035808

[7] Vagelli, A.A. (2011). The Banggai Cardinalfish: Natural History, Conservation, and Culture of Pterapogon kauderni. Wiley-Blackwell. https://www.wiley.com/en-us/shop/general-introductory-life-sciences/the-banggai-cardinalfish-natural-history-conservation-and-culture-of-pterapogon-kauderni-p-9780470654996

[8] IUCN (2007). Pterapogon kauderni. The IUCN Red List of Threatened Species. https://www.iucnredlist.org/species/63572/12692964

[9] Ndobe, S., Yasir, I., Moore, A.M., Biondo, M.V. & Foster, S.J. (2018). A Study to Assess the Impact of International Trade on the Conservation Status of Pterapogon kauderni (Banggai Cardinalfish). Report to the IUCN. https://www.researchgate.net/publication/340166021_Study_to_assess_the_impact_of_international_trade_on_the_conservation_status_of_Pterapogon_kauderni_Banggai_cardinalfish

[10] CITES (2007). CoP14 Proposal 19: Inclusion of Banggai Cardinalfish Pterapogon kauderni in Appendix II. https://cites.org/sites/default/files/eng/cop/14/prop/E14-P19.pdf

[11] CITES (2016). CoP17 Proposal 46: Inclusion of Banggai Cardinalfish Pterapogon kauderni in Appendix II. https://cites.org/sites/default/files/eng/cop/17/prop/060216/E-CoP17-Prop-47-REV2.pdf

[12] Grutter, A.S. (1999). Cleaner fish really do clean. Nature, 398, 672–673. https://doi.org/10.1038/19443

[13] Grutter, A.S., Murphy, J.M. & Choat, J.H. (2003). Cleaner fish drives local fish diversity on coral reefs. Current Biology, 13(1), 64–67.
https://doi.org/10.1016/S0960-9822(02)01393-3

[14] Waldie, P.A., Blomberg, S.P., Cheney, K.L., Goldizen, A.W. & Grutter, A.S. (2011). Long-term effects of the cleaner fish Labroides dimidiatus on coral reef fish communities. PLoS ONE, 6(6), e21201. https://doi.org/10.1371/journal.pone.0021201

[15] Michael, S.W. (2004). Reef Aquarium Fishes: 500+ Essential-to-Know Aquarium Species. Microcosm/T.F.H. ttps://archive.org/details/marinefishes500e0000mich/page/8/mode/2up

[16] DiMaggio, M.A., Cassiano, E.J., Barden, K.P., Ramee, S.W., Ohs, C.L. & Watson, C.A. (2017). First Record of Captive Larval Culture and Metamorphosis of the Pacific Blue Tang, Paracanthurus hepatus. Journal of the World Aquaculture Society, 48(3), 393–401. https://doi.org/10.1111/jwas.12426

[17] Sowaske, G., DiMaggio, M.A., Cassiano, E.J., Watson, C.A. & Ohs, C.L. (2023). Evaluation of larviculture protocols for the Pacific blue tang Paracanthurus hepatus. Aquaculture, 565, 739116. https://doi.org/10.1016/j.aquaculture.2022.739116

[18] Hixon, M.A., Johnson, D.W. & Sogard, S.M. (2014). BOFFFFs: on the importance of conserving old-growth age structure in fishery populations. ICES Journal of Marine Science, 71(8), 2171–2185. https://academic.oup.com/icesjms/article/71/8/2171/748104

[19] Leung, P.T.Y., O’Neill, S., Riginos, C., van Herwerden, L. & Sadovy de Mitcheson, Y. (2020). Population Genetic Structure of a Marine Pelagic Egg Producer and Popular Marine Aquarium Species, the Mandarinfish Synchiropus splendidus. Zoological Studies, 59, 68. https://pmc.ncbi.nlm.nih.gov/articles/PMC8181157/

[20] Mak, K.K.W., Yanase, H. & Renneberg, R. (2005). Cyanide fishing and cyanide detection in coral reef fish using chemical tests and biosensors. Biosensors and Bioelectronics, 20(12), 2581–2593. https://pubmed.ncbi.nlm.nih.gov/15854827

[21] Rubec, P.J. & Cruz, F.P. (2005). Monitoring the chain of custody to reduce delayed mortality of net-caught fish in the aquarium trade. SPC Live Reef Fish Information Bulletin, 13, 13–23. https://www.spc.int/DigitalLibrary/Doc/FAME/InfoBull/LRF/13/LRF13_13_Rubec.pdf

[22] Biondo, M.V. & Burki, R.P. (2019). Monitoring the trade in marine ornamental fishes through the European Trade Control and Expert System TRACES: Challenges and possibilities. Marine Policy, 108, 103620. https://www.sciencedirect.com/science/article/abs/pii/S0308597X19300193?via%3Dihub

[23] Wabnitz, C., Taylor, M., Green, E. & Razak, T. (2003). From Ocean to Aquarium: The Global Trade in Marine Ornamental Species. UNEP-WCMC. https://www.unep.org/resources/report/ocean-aquarium-global-trade-marine-ornamental-species

[24] Calado, R., Olivotto, I., Planas, M. & Holt, G.J. (eds.) (2017). Marine Ornamental Species Aquaculture. Wiley-Blackwell. https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1749-7345.2011.00453.x

[25] Jones, A.M., Gardner, S. & Sinclair, W. (2008). Losing “Nemo”: bleaching and collection appear to reduce inshore populations of anemonefishes. Journal of Fish Biology, 73(3), 753–761. https://onlinelibrary.wiley.com/doi/10.1111/j.1095-8649.2008.01969.x