Monos, family Monodactylidae

Monos, family Monodactylidae

Three species of mono are traded, Monodactlyus argenteus, Monodactylus kottelati, and Monodactylus sebae. The first two species are not distinguished in the hobby and are simply called common monos or Malayan angels. The third species is known as the West African mono and is easily distinguished.

All three species require the same basic care. They are not fussy about salinity, though adults at least fare best in moderate to high-end systems (SG 1.010 upwards). High levels of carbonate hardness are essential, and the use of calcareous material, such as crushed coral, in the filter to provide this is recommended. A protein skimmer will help maintain good water quality. Monos are primarily plankton and detritus feeders in the wild, and in aquaria will eat most foods including flake and pellets. They are lightning-fast animals, and need plenty of swimming room; Monodactlyus argenteus and Monodactylus sebae at least should not be kept in a tank less than 120 cm long.

Monos are essentially quite robust, particularly once settled in. It is easier to introduce juveniles into an aquarium than adults. Adults seem to be sensitive to shock when moved, turning black instead of their normal silver. Left alone they will recover eventually. In the wild, juvenile monos are reported to live singly or in small groups, forming large groups only as they mature and move into open water. Under aquarium conditions the adults tend to be highly territorial and sometimes aggressive towards other members of their species if overcrowded. Odd numbers of specimens work best if you want to keep them in groups. Different mono species mix well, and they also mix well with scats, and keeping them in mixed species groups seems to moderate their aggression somewhat.

Not much is known about the breeding behaviour of these fishes. They appear to spawn in freshwater, and the few reports of breeding in home aquaria have occurred when these fish were being maintained in freshwater conditions. Since these fish are more disease-prone when kept in freshwater tanks, maintaining them under such conditions is not recommended, and attempts to breed these fish are best left to expert fishkeepers able to move them between fresh and brackish water tanks as required.

Distinguishing the common species of Monodactylus

Monodactylus argenteus is the most widely traded species. This fish is found from South Africa east to Australia. It has a circular body bearing triangular dorsal and anal fins of similar size. The dorsal fin is marked with yellow (though this may fade to orange as the fish mature). In captivity this species can be expected to reach a length of 15 cm (6 inches) though it does get much bigger in the wild.
Very similar to the the common mono is Monodactylus kottelati. It has a similar shape, but the dorsal fin is not as tall as the anal fin is deep. This is the most reliable way to distinguish the two species. In addition, the dorsal fin on this species tends to be orange, whereas on the common mono this fin is yellow. It is a small species said to reach no more than 8 cm in the wild, though maximum size in captivity is uncertain given the problems distinguishing it from M. argenteus.
Restricted to Africa is the fingerfish Monodactylus sebae which is much more deep (and angelfish like). It lacks the yellow of the Malayan angel, but the dark grey or black bands running from the dorsal to the anal fin are much bolder. This fish is much deeper than it is long, and needs plenty of depth. Don’t keep adult fingerfish in aquaria less than 60 cm (24 inches) deep.