The mono, Monodactylus spp, is a member of a family of fish commonly known as fingerfishes. They are often mistaken for angelfish but are really quite different in appearance and habitat. Natives of the Indo-Pacific, the mono makes its home near coastlines and estuaries. As juveniles, they thrive in both fresh and brackish water. Brackish is a term that refers to the water in areas where rivers flow into the oceans. The water has a higher salt content than fresh but lower than that of sea water and is typically murky. As they mature, the adult fish typically make there home in saltwater. The most commonly kept species are Monodactylus argenteus and Monodactylus sebae.
Appearance and Behavior
Monos are typically silver with yellow fins and one or two black bars running vertically across the first third of the body. They are disc shaped with small dorsal and pectoral fins. A prominent lateral line canal courses horizontally over the top third of the body. This canal is a series of organs designed to recognize electrical impulses produced by other fish and helps them find food and avoid predation. Monos can reach an adult length of 6 to 9 inches but 3 to 6 inches would be more the expected length when kept in an aquarium. These fish are active swimmers and move constantly. They are difficult to catch and are often injured in the process. Despite their flashy appearance, monos hang out in their native habitats in dirty, murky water where they are active scavengers. In the aquarium, they will eat most anything offered from both plant and animal sources. Since they swim constantly, a long tank with plenty of room is best. Monodactylus sebae, the striped fingerfish, is a less commonly seen species that does best with a few companions.
Feeding and Tank Requirements
If your fish are healthy they will be eating all sorts of foods. They are not picky eaters but offering a wide variety of plant and animal source foods will keep their appetites keen. With time, they may come to the surface to feed, or may pick up the scraps at the bottom of the tank. If you are keeping your fish in saltwater, average tank conditions are adequate. To create a brackish environment for younger species or those not yet acclimated to saltwater, add a tablespoon of aquarium salt to a gallon of water or saltwater mix to a specific gravity of 1.010-1.015. Keep the temperature between 74 and 80 degrees Fahrenheit. When you acquire your monos, make sure and ask your supplier whether they have been kept in a fresh, brackish or saltwater environment. Try to reproduce those conditions initially before making any changes.
Just because monos like to hang out in murky water doesn't mean you should try and reproduce those conditions in your tank by neglecting normal cleaning. By providing a consistent food source, monos will do very nicely in your well-maintained and filtered aquarium. If you want to try a few brackish water companions, try adding a scat or target fish.