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.
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.
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.
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.
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.