Home | Aquarium Livestock | Keeping Brackish Water Fish – the Silver Mono or Malayan Angelfish

Keeping Brackish Water Fish – the Silver Mono or Malayan Angelfish

Large, flashy, uniquely-shaped and active, Silver Monos, Monodactylus argenteus, always draw attention when seen for the first time.  But there are many misconceptions concerning their proper care, and new owners often become frustrated with them and move on to other interests.  However, when their unique needs are met, Monos are quite hardy and make for spectacular exhibits.  A group I cared for at the Bronx Zoo, housed with Mudskippers, Fiddler Crabs and Banded Archerfish, proved so interesting that they rivaled neighboring Leaf Insects, Hornbills and Tapirs for visitors’ attentions.

Mono School

Uploaded to Wikipedia Commons by Brocken Inaglory


The Mono’s silvery coloration shimmers under light, and is nicely offset by yellow or black fin tips and the jet-black stripe that runs along the edges of the dorsal and anal fins.  The body is flattened and disc-shaped, and the sturdy dorsal and anal fins are much-elongated.  Silver Monos are powerful swimmers, well-able to buck the strong currents common to the tidal rivers and coastal mangroves that they frequent.  If given enough space and a proper diet, they can reach 9- 10 inches in length, but most in the pet trade top out at half that.

This fish is sold under a variety of common names, including Moonfish, Malayan Angelfish and Silver Moony.

Natural History

The Silver Mono has a huge range, being found along the Indian Ocean coastlines of East Africa, Madagascar and India, throughout Southeast Asia to the Philippines and Australia and in the Western Pacific from the coast of southern Japan to New Caledonia.

Brackish mangrove swamps and the mouths of tidal creeks and rivers are the typical habitats of younger animals (please see photo).  Adults also utilize coastal reefs and other marine environments.

Despite its wide distribution, Silver Mono populations are not secure, as the mangrove swamps and estuaries upon which they depend are among the earth’s most threatened habitats.

Silver Monos

Uploaded to Wikipedia Commons by TANAKA Juuyoh

The Aquarium

Monos school throughout life, and do best when kept with others of their kind.  Plan on a 55 gallon aquarium for 2 adults, or a 75-100 for 4-6 individuals.

I’m not sure if the Mono’s flattened body is an adaptation to life among sea grass and mangrove roots, but those I’ve kept did dart into such cover when disturbed by unruly zoo visitors.  Live Java Ferns, Sea Cactus, Caulerpa and similar plants and alga, along with artificial mangrove roots (this model is safe for use in marine aquariums) will add greatly to your set-up.  Experimentation is necessary, as some plants may be sampled or eaten. Please see this article for more information on using live plants in brackish water aquariums.

Salinity, pH, and Temperature

Youngsters will do well in typical brackish water aquariums at a specific gravity of 1.005.  Fluctuations in salinity (i.e. between 1.002 and 1.007) are well-tolerated and may even be beneficial.

In the wild, adults often move offshore, where they adapt to ocean water.  For this reason, most experienced keepers advise gradually increasing the salinity as one’s fishes mature.  I’ve done well by keeping adults at 1.007, but others report success under purely marine conditions.

Poorly-informed fish retailers, perhaps in order to increase sales, may suggest that you can habituate Monos to fresh water.  This is untrue – wild individuals do not travel out of tidal regions (brackish and salt water), and captives will not thrive in freshwater aquariums.

A pH of 7.2 – 9 and temperature range of 72-82 F suit them well.  I generally used 8.0 and temperatures of 78-82 F.

Tidal River and nearby coast

Uploaded to Wikipedia Commons by Feydey


I’ve successfully kept Silver Monos with Banded Archerfishes, Mudskippers, Scats, Bumblebee Gobies, Hermit and Fiddler Crabs and various snails.


Silver Monos are opportunistic feeders and will readily consume all manner of flake, pelleted and frozen fish foods.  Mine relished live insects, black worms and tiny shrimp above all else, and were also provided occasional meals of wild-caught moths, spiders and beetles.  Mangrove swamps support a huge diversity of insect species, some of which play an important role in the diets of resident brackish water fishes.

I base the balance of the diet on frozen prawn, clams and other “meaty” foods.  Individuals maintained on flakes and pellets alone do not do as well as those provided a diet comprised of insects and frozen marine invertebrates.

Plant-based foods are also important.  Kale and other greens (first softened by a 5 minute soak in hot water), various marine algae (seaweed), Spirulina and fresh-water plants should be offered regularly.

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Further Reading

Archerfish Care and Natural History

Mudskippers – Blurring the Line Between Fishes and Amphibians


  1. avatar

    I have a slight situation where I live 20 miles from the store and after changing the water discovered that I don’t have enough instant ocean. The salinity is below what I have been guided to use. I can’t get more salt until over 24 hours. Will my Mono die?!? I’m so upset. I should have checked to make sure I had enough salt, but now it is too late. I won’t be able to get back here with salt until tomorrow night! (either lose my job or save my fish basically) …. so stressed. I hope he doesn’t die. I’ve had him around 10 years now.

  2. avatar

    Hello Dawn,

    They experience wide salinity fluctuations in the wild, so usually adapt well…the only problem could be a sudden change after years at the same salinity; unfortunately, no way to predict. When you get the salt, bring the salinity up gradually, so as not to subject the fish to another shock. That’s a nice longevity….I hope all goes well, pl keep me posted, Frank

  3. avatar

    Hello sir! I have kept mono angel with silver sharks in a brackish water. They died very soon. Can u please help me how to setup a fishtank adequate for mono angel as I want to keep a family onlying of mono angel.

  4. avatar


    I’m not sure what information you are seeking -please check the article for details as to temperature, salinity etc, and let me know if you have any specific questions…best regard, Frank

  5. avatar

    My question is what are the preventive measures to be taken to safeguard mono Angels in an aquarium?
    Do they require a complete salt environment?

  6. avatar


    They can be kept at a specific gravity range of 1.002 and 1.007, but some people report success keeping them as purely-marine fish (i.e. 1.020). Best, frank

  7. avatar

    My mono angel is infected I tried to clean him with my hands softly but after few minute he behave like ded what to do is he dide ?

  8. avatar

    Hello Nilay, I wouldn’t be able to tell you if your fish has died or not. Is it moving? Breathing? Swimming? What do you mean when you say you “clean him” and that it is “infected”? Also, what are the water parameters in the tank – pH, Ammonia, Nitrite, Nitrate, temperature, salinity at least to start with? If you can provide more information about your fish and tank, I can try to help you with it.

  9. avatar

    Hello sir can I put parrots with mono angels????
    I have a 55 gallon tank and I am fan of both

  10. avatar

    Hello Anonymous, Are you interested in keeping Mono’s or Angelfish? Mono’s are brackish water as discussed in this blog and wouldn’t be suitable with freshwater Parrotfish or Angelfish. In a 55-gallon aquarium, I would recommend choosing either Angelfish OR Parrotfish, not both.

  11. avatar

    I noticed you said you have kept monos with bumblebee gobies, were you keeping adult monos with bumblebees? And if so, for how long were you able to keep the bumblebees alive? I have a very successful mono setup for three years now, but I’ve never had good success with bumblebees. From what I’ve read, they are really more a freshwater to low brackish fish, while adult monos really should be kept high brackish to full saltwater. Also, bumblebees tend to stay on the bottom, hide, and are finicky eaters, while monos are gregarious eaters, it seems theyd eat any food before it gets to the bumblebees. How do you keep the bumblebees healthy and well fed in the same tank with monos?

  12. avatar

    Hello Mark, Just like Mono’s and most brackish water fish, the Bumblebee Gobies start in almost full freshwater when young and can tolerate increasing salinity as they age. Adding them to a higher salinity tank right away isn’t a good idea, but if you start the tank out with a lower salinity and increase it over time, they can usually adjust. They would need to be target-fed if being kept in a larger tank with fish that may outcompete them for food. You can try feeding them through a tube to the food can reach the bottom without being eaten by the other fish in the tank if nothing is making it to them at the bottom.

  13. avatar

    why my mono fish is chasing another mono fish?

  14. avatar

    Hi Fazil, There could be a number of reasons why one fish would chase another. Depending on the size of the aquarium, it may be aggression or a lack of space for proper territories. If you have a male and female, it may be a breeding behavior.

  15. avatar

    Hi I’m seeking you guidance please, I’m in a desperate situation, need your kind help. I live in Sri Lanka I been looking for so long and I have got some moon angels for my self, I was advised by the store that they can be kept in fresh water as they were in the store, at first I got 5 pairs of them all died due to the power outage as there wasn’t any oxygen, left the lid open still that wasn’t enough, before they died they got white spots on the body any way I got 3 more pairs more they are better than the last batch but still they have white spots on the body, what should I do any treatments that u would recommend please help

  16. avatar

    Hi Rumeah, Mono’s are brackish to full saltwater as discussed here and shouldn’t be kept in freshwater. “White spots” can be a sign of many different conditions so recommending a treatment without more information is difficult. If you’d like, you can email us photos of the fish as well as more information about your tank (size, temperature, water parameters like Ammonia, Nitrite, Nitrate, pH, salinity) to fish@thatpetplace.com and we can try to diagnose and recommend a treatment for you.

  17. avatar

    At what age or size can Monos be introduced to salt water?

  18. avatar

    Hi Dave, They should be in at least lightly brackish to start and can be slowly acclimated to full saltwater as they mature. Since it is difficult to determine age, I would recommend slowly increasing to full salinity over 1-2 years, depending on what the starting salinity was.

About Frank Indiviglio

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Being born with a deep interest in animals might seem unfortunate for a native Bronxite , but my family encouraged my interest and the menagerie that sprung from it. Jobs with pet stores and importers had me caring for a fantastic assortment of reptiles and amphibians. After a detour as a lawyer, I was hired as a Bronx Zoo animal keeper and was soon caring for gharials, goliath frogs, king cobras and everything in-between. Research has taken me in pursuit of anacondas, Orinoco crocodiles and other animals in locales ranging from Venezuela’s llanos to Tortuguero’s beaches. Now, after 20+ years with the Bronx Zoo, I am a consultant for several zoos and museums. I have spent time in Japan, and often exchange ideas with zoologists there. I have written books on salamanders, geckos and other “herps”, discussed reptile-keeping on television and presented papers at conferences. A Master’s Degree in biology has led to teaching opportunities. My work puts me in contact with thousands of hobbyists keeping an array of pets. Without fail, I have learned much from them and hope, dear readers, that you will be generous in sharing your thoughts on this blog and web site. For a complete biography of my experience click here.