Monos (monodactylus argenteus) are disc shaped fish from the coastal areas of Australia and the Red Sea. They are often called fingerfish. They belong to the family Monodactylidae.
If you plan on keeping monos in your aquarium you will need a large one. Monos grow up to 9 inches in diameter (23 cm). Monos are shoaling fish and so you need to have a large enough tank to house at least 4-6 of them. The monos you find in pet stores will most likely be juveniles and so keep their adult size in mind when choosing their aquarium.
A species tank is recommended. Monos swim fast and they grow large enough to eat smaller fish. Monos also frighten easily and so you can't keep them with aggressive species of fish. Don't keep monos as solitary fish. They need members of their own species present in order to thrive.
Monos prefer brackish water, but juveniles are able to survive in freshwater. Juvenile monos typically need less salt in their water than older monos. In fact, in their natural environment, older monos usually live in a complete saltwater environment. Because of this, it is recommended that you increase the salinity of the tank as the fish ages.
Juveniles can survive in freshwater as long as the water is hard (having a high dissolved mineral ion content). The water temperature should be about 77 °F (25 °C). The water should be slightly alkaline (pH of 7.2) and it is best if you add some salt to the tank (even for the juveniles). Add about 2 tablespoons of aquarium salt per 5 gallons of water (20 liters). Gradually increase the salinity to that of full seawater as the fish ages.
They will eat flakes, frozen, freeze-dried, and live foods. They are omnivores, eating both meaty and plant based foods.
Sexing fingerfish is difficult because males and females look identical. There have been no reports of successful breeding of fingerfish in the aquarium.
Monos can be purchased for around $15-20.