Monos Fish
Species NameMonodactylus argenteus
Common NameMono, Silver Mono, Moonfish, Fingerfish
Care LevelModerate
Lifespan7-10 years
Adult SizeUp to 9 inches (23 cm)
Minimum Tank Size125 gallons
Temperature72°F – 82°F (22°C – 28°C)
Water ConditionspH 7.5-8.5, Salinity varies with age

About the Monos – Species Summary

The Mono, scientifically known as Monodactylus argenteus, is an intriguing brackish water fish that captivates aquarists globally. Originating from the coastal waters and estuaries of Africa, Asia, and Australia, this diamond-shaped fish is not only revered for its silver, shimmering appearance but also its distinct fin structures and unique demeanor. Monos, often called Moonfish or Fingerfish, transition from freshwater conditions as juveniles to more saline environments as adults, making their care journey a captivating experience for those passionate about aquatics.

Monos Lifespan

Monos, when cared for under the right conditions and provided with a suitable diet, typically enjoy a lifespan ranging from 7 to 10 years. These numbers can vary based on factors such as their living environment, diet quality, and overall health. Regular health checks and timely interventions can play a crucial role in ensuring they live to their maximum potential age.


The Mono is instantly recognizable with its almost disc-shaped, laterally compressed body. Its silver body, combined with a black band that runs across its eyes and wraps around the back, adds to its mesmerizing charm. Their dorsal and anal fins are long, extending almost the full length of their bodies, giving them a unique silhouette against the aquarium backdrop.

Average Size

Upon reaching full maturity, Monos can attain sizes of up to 9 inches or approximately 23 centimeters.

Monos Care

Tank Size

Given the active nature and adult size of Monos, a minimum tank size of 125 gallons is recommended. This ensures they have adequate space for swimming and reduces the potential stress from confinement.

How To Set Up Their Tank

When setting up a tank for Monos, the primary consideration should be their need for brackish water as adults. As juveniles, they begin life in freshwater conditions, but as they grow, the salinity needs to be gradually increased. A substrate of fine sand, complemented by rock structures or driftwood, can offer them a semblance of their natural habitat. Ensure a good filtration system is in place, given their sensitivity to water quality.

Lighting Requirements

Monos don’t have specific lighting demands. However, a moderate light setup that simulates a day-night cycle is beneficial. Ambient room light supplemented with aquarium lights would be adequate.


Maintaining a pH level between 7.5 to 8.5 is crucial for the health and well-being of Monos.


The water temperature should consistently lie between 72°F and 82°F (22°C to 28°C).

Water Parameters

Apart from pH and temperature, it’s essential to pay attention to the salinity, especially as Monos age. Juvenile Monos thrive in freshwater, but as they grow, the salinity should be gradually increased to a brackish state. Regularly test the water for ammonia, nitrites, and nitrates to ensure a healthy environment.

Disease Potential

Monos, like many other fish, are susceptible to common aquatic diseases such as Ich and fin rot. Quarantining new additions and ensuring water parameters remain stable are key preventive measures. Should they show signs of disease, prompt diagnosis and treatment are imperative.

Food & Diet

Monos are omnivores and enjoy a varied diet. While they’ll happily consume flakes and pellets designed for brackish fish, it’s a good practice to supplement this with live or frozen foods like brine shrimp or bloodworms. Occasional plant matter, such as spirulina, can also be included for dietary diversity.

Behavior and Temperament

Monos are schooling fish and are best kept in groups of five or more. They are generally peaceful but can become territorial or show semi-aggressive tendencies, especially if kept in cramped conditions or if their school is too small.

Tank Mates

Given their relatively peaceful disposition, Monos can cohabit with a range of brackish water species. Good tank mates include Archerfish, Mollies adapted to brackish conditions, and larger Gobies. However, smaller fish might become food, so it’s prudent to choose tank mates that are neither too aggressive nor too small.


Breeding Monos in captivity is a rare and challenging endeavor, mainly because they require specific water conditions and triggers to breed. Those who aim to breed Monos need to ensure that they are in a comfortable environment, with optimal water parameters and a diet rich in live foods. Observing courtship behaviors can be fascinating, but successful breeding requires patience and a deep understanding of their needs.

Monos FAQs (Frequently Asked Questions)