The Mono Fish is a shiny diamond shaped fish that’s perfect for the brackish water aquarium!

The Mono Monodactylus argenteus is a beautiful silvery fish that definitely has a place in any brackish aquarium. This Silver Moony is one of the aquarium favorites. It is a good sized fish, deep bodied and laterally compressed with an attractive roundish diamond shape.

Overall the Mono Fish is silver in color highlighted with a light yellow on the dorsal, anal and tail fins. Two vertical black stripes adorn the front, one running through the eye and a second across the gill. When they are young they also have a bright yellow dorsal fin which adds to their appeal. The disc-like shape and shiny silver color have led to all sorts of descriptive common names like Silver Moony, Silver Moonfish, Silver Batfish, Diamond Moonfish, Diamondfish, Fingerfish, Kitefish, and even Malayan Angel.

The Moonfish, Scats and Archerfish are the quintessential brackish water fish. They are all big, attractively patterned, and very durable. Almost every brackish aquarium will include at least one these types. This Moony will grow up to about 6 inches (15 cm) in the aquarium. They must be kept in schools however, as individuals are too nervous to be kept on their own. But they are a peaceful shoaling fish and a school of these fish are a beautiful sight. Mono’s and Scats mix well with each other too, and a mixed school of these species can be kept with great success.

If kept correctly, a school of Mono Argentus will give you many years of enjoyment. The Mono is suggested for a more experienced fish keeper because of their need to change water conditions as they age. Some Moon Fish will survive for awhile in a freshwater environment when young, but as adults they really are brackish water fish. Adults can even be acclimated to a full saltwater environment. If you are up for that challenge these fish are easy to feed and will take a variety of foods.

Mono Fish are lively and entertaining to watch, but they are also timid and easily frightened. Keep them with peaceful tank mates, but not too little as they may eat smaller fish. They are hearty eaters and enjoy a variety of foods from live and frozen foods to flakes, and will even munch on lettuce and spinach.


Scientific Classification


Mono Fish – Quick Aquarium Care

Aquarist Experience Level:Advanced
Aquarium Hardiness:Moderately Difficult
Minimum Tank Size:55 gal (208 L)
Size of fish – inches10.6 inches (27.00 cm)
Temperature:75.0 to 82.0° F (23.9 to 27.8&deg C)

Habitat: Distribution / Background

The Mono Monodactylus argenteus was described by Linnaeus in 1758. The Mono Fish has a very large distribution. They are found in the Red Sea, along the coasts of Australia, Eastern Africa and throughout Southeast Asia. The Mono Argentus is not listed on the IUCN Red List. Other names this fish is commonly known by are Silver Moony, Silver moonfish, Moonfish, Silver Batfish, Diamond Moonfish, Diamondfish, Fingerfish, Kitefish, Singapore Angelfish, Moony, Moonyfish, and Malayan Angel.

Mono Fish are found in schools in the shallow portions of estuaries, inshore reefs, and fresh water tidal pools. The adult fish will normally inhabit the coastal areas and the juveniles will stay more in brackish environments. In nature the Mono will eat a variety of plant matter, detritus, and insects.

  • Scientific Name: Monodactylus argenteus
  • Social Grouping: Groups
  • IUCN Red List: NE – Not Evaluated or not listed


The Mono Argentus is a disc- shaped fish with a flattened body, similar to that of a freshwater Angelfish minus the feelers. Mono Fish can reach up to 11 inches (27 cm) in the wild. In the aquarium they will generally not get much bigger than about 6 inches (15 cm) with a life span of about 7 – 10 years.

The body coloration of the Mono is a shiny silver with light yellow coloring on the dorsal, anal and tail fins. There are two vertical black bands, one extending through the eye with another just behind it that extends across the body and along the front edges of the dorsal and anal fin. Juveniles have a brighter yellow dorsal fin.

  • Size of fish – inches: 10.6 inches (27.00 cm) – Tank raised specimens rarely grow larger than 6 inches (15 cm).
  • Lifespan: 7 years – The Mono has a lifespan of about 7-10 years.

Fish Keeping Difficulty

The Mono Fish is suggested for a more experienced fish keeper as they must be kept in strongly brackish or marine aquariums. A great deal of experience is need to successfully house these fish, but for an experience aquarist they will present no particular problems. To successfully change water conditions as the fish ages can be a challenge. In addition to a good sized tank, the only other requirement is clean, well filtered water. If you are up for that challenge these fish are easy to feed and will take a variety of foods.

  • Aquarium Hardiness: Moderately Difficult
  • Aquarist Experience Level: Advanced

Foods and Feeding

The Mono Fish is an omnivorous species. In the wild they feed on a variety of plant matter, detritus, and insects. Although in the aquarium they will eat dried foods, they really should be fed a varied diet consisting of fresh or frozen foods such as brine shrimp or bloodworms. They can also be offered some vegetable matter such as algae, blanched lettuce and spinach, and boiled peas.

  • Diet Type: Omnivore
  • Flake Food: Yes
  • Tablet / Pellet: Yes
  • Live foods (fishes, shrimps, worms): Some of Diet
  • Vegetable Food: Some of Diet
  • Meaty Food: Some of Diet
  • Feeding Frequency: Several feedings per day

Aquarium Care

Some Mono Fish will survive for awhile in pure freshwater but they really are brackish water fish. These fish are also greedy, fast growing feeders and produce a lot of waste. They need quality water conditions and so a powerful filter is essential. Their tank should be cleaned weekly and have at least a 30% water change done.

  • Water Changes: Weekly – Do at least a 30% water change weekly.

Aquarium Setup

Monos will swim in all parts of the aquarium. A minimum school size of at least five Mono Fish is recommended, with more being better. Pairs and trios They will need at least a 55 gallon aquarium with plenty of aeration. As they grow an upgraded tank will be needed. Some Monos will survive for awhile in pure freshwater but they really are brackish water fish. Their aquarium water should be made brackish by the addition of some high quality marine water salt mix, approximately 2 – 3 teaspoons per gallon. This species will also do very well in pure saltwater and usually looks their best when kept this way.

For substrate use a fine gravel or sand. A high efficient undergravel filter will work well to keep the oxygen level high in the tank. A efficient canister filter will work well with these aggressive, messy eaters. Monos need plenty of swimming space and driftwood, branches and roots make good decor and an area for the fish to entertain themselves.

  • Minimum Tank Size: 55 gal (208 L)
  • Suitable for Nano Tank: No
  • Substrate Type: Sand/Gravel Mix
  • Lighting Needs: Moderate – normal lighting
  • Temperature: 75.0 to 82.0° F (23.9 to 27.8&deg C)
  • Range ph: 7.2-8.5
  • Hardness Range: 8 – 14 dGH
  • Brackish: Yes – Adults must be kept in strongly brackish water or fully marine aquariums.
  • Water Movement: Moderate
  • Water Region: All

Social Behaviors

A schooling fish, the Monos do best in groups of 5 or more. They are relatively peaceful fish, but they do squabble within their ranks. Fish kept in pairs or even trios rarely work out, as there is no room to spread out aggression. These fish develop a hierarchy within their school, with the largest fish being more dominant and feeding first.

They are lively and rambunctious, but they are peaceful with their other tank mates. They may eat small fish and shrimp and they are easily intimidated by large or aggressive fish. So be sure none of their tank mates are likely to ever grow to be much larger than the Monos will, and also be sure their tank mates aren’t bite size.

Never include Monos and freshwater Angelfish in the same tank. Angelfish have two ‘feelers’ in front of the bottom fin. Monos natural clean each other and when they see an angelfish, they try to clean the feelers off of them. It is said that Mono’s think Angelfish are also Monos and don’t understand that their feelers are suppose to be there. Good choices would be larger Mollies, as well as Archerfish, Scats, and brackish species of Gobies.

  • Venomous: No
  • Temperament: Semi-aggressive
  • Compatible with:
    • Same species – conspecifics: Yes – Groups of 5 or more are necessary.
    • Peaceful fish (): Monitor – They will eat smaller fish.
    • Semi-Aggressive (): Monitor
    • Aggressive (): Threat
    • Large Semi-Aggressive (): Threat
    • Large Aggressive, Predatory (): Threat
    • Monitor
    • Shrimps, Crabs, Snails: Threat – is aggressive
    • Plants: Safe

Sexual differences

Sexual differences are unknown.

Breeding / Reproduction

The Monodactylus Argenteus has not been bred in captivity. There are reports of accidental spawning activity, but this behavior hasn’t been successfully duplicated.

  • Ease of Breeding: Difficult

Fish Diseases

With the Mono Fish disease is not usually a problem in a well maintained aquarium. That being said there is no guarantee that you won’t have to deal with health problems or disease. Anything you add to your tank can bring disease to your tank. Not only other fish but plants, substrate, and decorations can harbor bacteria. Take great care and make sure to properly clean or quarantine anything that you add to an established tank so not to upset the balance. Banded Archer are very resilient once established in a tank.

A good thing about the Mono is that due to their resilience, an outbreak of disease can often be limited to just one or a few fishes if you deal with it at an early stage. When keeping more sensitive types of fish, it is common for all fishes to be infected even before the first warning signs can be noticed. The best way to proactively prevent disease is to give your Mono the proper environment and give them a well balanced diet. The closer to their natural habitat the less stress the fish will have, making them healthier and happy A stressed fish will is more likely to acquire disease.

Mono are fairly hardy fish if their water requirements are met, but are subject to the same diseases as other tropical fish. One of the most common freshwater fish ailments is ich.It is recommended to read up on the common tank diseases. Knowing the signs and catching and treating them early makes a huge difference. For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.


This species of Monodactylus, the Mono or Mono Argentus M. argenteus, is commonly available.



Featured Image Credit: Pavaphon Supanantananont, Shutterstock