Scats and Monos are often mentioned in the same breath because their requirements are so similar. They also get along extremely well, and together bringing both colour and personality to the brackish water community. Both belong to rather small Old World families of perciform fish, the Scats from the Scatophagidae and the Monos from the Monodactylidae. There are only two genera in the family Scatophagidae, Scatophagus and Selenotoca, both of which provide species traded as aquarium fish. The Monodactylidae also comprise two genera, Monodactylus and Schuettea, but only species of Monodactylus are kept in home aquaria.

Scats: Adaptable Omnivores

Scats are roughly oval in shape but with a compact head and rather dainty mouth. Maximum size can be anything up to 40 cm/16" in the wild but that is very uncommon in home aquaria, where most specimens only get to about 15-20 cm/6-8". According to at least some authors, the spines in the dorsal, anal, and pelvic fins are equipped with venom glands.

Aquarium Care

Scats are incredibly hardy and robust fish. They travel well, settle into new aquaria quickly, and show no reticence at feeding time. The main, and arguably only, problem with Scats is their relatively large and consequent need for a big, well-filtered aquarium. Given that most specimens will be at least 15 cm/6" once mature, and potentially quite a bit bigger, they should not be kept in a tank less than 120 cm/4' in length or 200 litres/55 gallons in capacity. The filter system used should be appropriate to the messiness of the fish, and ideally should provide a turnover of not less than 6 times the volume of the tank in turnover per hour.

Water Chemistry

In the wild Scats prefer shallow coastlines, mangroves, harbours, and estuaries. Although they are found in the sea, they are never found far from land, and typically only in water less than 4 m/12' deep. Scats will sometimes make long expeditions in land, swimming well into the freshwater parts of river systems, and have been reported as much as 50 km/30 miles inland. Unsurprisingly they are very adaptable as far as water chemistry goes.

Scats can be kept as freshwater fish for quite long periods, but under such conditions do tend to be prone to various diseases including Finrot, Lymphocystis, and Pop-Eye. They do much better maintained at 25-50% seawater salinity (SG 1.005-1.012). The precise salinity doesn't matter greatly, though for the sake of the biological filter you should not let it vary too much between water changes. At fairly high salinities (SG 1.010 upwards) protein skimmers work sufficiently well for them to make a valuable contribution to water quality management.

In Marine Aquaria

Scats are sometimes kept in large reef systems, but they cannot really be called completely reef safe fish because of their omnivorous palate. While they will not harm crustaceans, echinoderms or cnidarians, things like tubeworms and macroalgae will simply be viewed as food. On the other hand, Scats make superb additions to fish-only community tanks. In fact both Scats and Monos are almost ubiquitous in public aquaria where they are kept alongside groupers, sharks, etc.

Diet

Scats will eat practically anything, and the scientific name Scatophagus literally means "dung eater", a reference to the fact these fish are commonly found hanging about sewage outfall pipes. Unsurprisingly they are not esteemed as food fish, though they are edible and supposedly rather tasty when absolutely fresh. In any case, the aquarist should provide them with a mixed diet containing both meaty and green foods, but precisely what couldn't matter less. Flake, pellets, frozen foods, tinned peas, spinach and algae are all greedily taken. Scats will also eat aquarium plants of all types, including Java fern, though the authors of Baensch's Aquarium Atlas report that Scats that ate Java ferns died shortly afterwards, presumably poisoned by this toxic plant. Scats are inept predators, though they may well eat fish eggs and fry.

Scats are intelligent fish that quickly learn to beg for food. They will also learn to recognise other sources of food; the author kept a specimen that learned to follow archerfish around so that it could steal the food items that the archers knocked into the water!

Social Behaviour

Scats are non-aggressive, non-territorial fish but they can be a bit boisterous so don't keep them with anything excessively shy or nervous. Scats can do well kept alone, but keeping them in groups of at least three specimens is recommended. Ideal tankmates include Monos, Archerfish, Mollies, Chromides, Sleeper Gobies, and Colombian Shark Catfish.

Breeding

Scats apparently spawn in the sea with the larvae passing through a planktonic stage before migrating into estuaries. Reports of spawning in aquaria are very scarce, but there are suggestions the adults guard the eggs in a cichlid-like manner.

Species

The most common species is Scatophagus argus, known as the Spotted Scat or Common Scat. Maximum size in the wild is at least 35 cm/14", though in captivity most specimens only get to about two-thirds that size. Juveniles are a bright brass colour with numerous black spots on the flanks and usually one or more vertical bands on the head. In some cases there are red markings on the dorsal surface, particularly across the forehead and dorsal fin. As the fish mature the contrast between the spots and the background colour lessens somewhat, and the overall colour shifts from brass to a green-brown bronze tone.

There is a lot of variation in the colouration of this species, and some forms have been traded separately from the standard form. The Red-Headed Scat is one such form, noted for the extensive red markings on the dorsal surface. It is also known by various invalid scientific names including Scatophagus atromaculatus, Scatophagus ornatus, and Scatophagus rubrifrons. The Hooghly River Scat is another variant, this time with large blotches rather than spots on the flanks.

The Silver Scat Selenotoca multifasciata is one of the prettiest fish in the hobby. It has a brilliant silver body with black spots and vertical bars across the face and flanks. Maximum size in aquaria is rarely more than 15 cm/6" though wild fish supposedly reach up to 40 cm/16". A related species Selenotoca papuensis may be traded occasionally. It is essentially identical in appearance though maximum size is said to be less than 10 cm/4". Distinguishing the two species is very difficult, though one indicator may be the size of black spots on the body: in the case of Selenotoca multifasciata these are smaller than the size of the eye, whereas on Selenotoca papuensis the spots are about the same size as the eyes.

The least widely seen (and easily the most expensive) species of Scat is the Striped Scat or African Scat Scatophagus tetracanthus. It has a yellowy-silver body with a variable number of thick vertical bands running across the face and flanks. There are also some red and yellow patches on the dorsal and anal fins. The result is an extremely attractive fish that looks more like a butterflyfish from a marine tank than anything else. Although very rare in the trade, it is no more difficult to keep than the other Scats. Maximum size in the wild is said to be 30 cm/12", but in common with the other Scats aquarium specimens are much smaller.

Monos: Brackish-Water Butterflies

All the traded Monos come from the one genus Monodactylus. They are remarkable for being incredibly active and very agile swimmers, and quite probably rank among the fastest fish kept in aquaria. They are extremely difficult to catch with a net! Most species get to about 15 cm/6" in captivity, so while not quite so large as Scats certainly need ample swimming room to do well.

Aquarium Care

Basic care is similar to the Scats, the main difference being Monos are temperamental and travel poorly. When introduced to a new aquarium they should be treated gently and the lights should be left off to give them time to settle down. They often turn black and breathe heavily when stressed (and at night). Although fatalities are uncommon if handled and transported carefully, they are exceedingly sensitive to oxygen depravation and can suffocate in small bags or buckets.

Water Chemistry

Again, water chemistry is similar to Scats. Hard, alkaline water maintained at 25-50% seawater salinity (SG 1.005-1.012) will suit them well. As with Scats, Monos migrate in and out of rivers all the time, and there's no need to raise the salinity as they mature.

In Marine Aquaria

Monos are potentially predatory and eat a wide variety of animal prey including small crustaceans; consequently their usefulness in reef tanks is a bit limited. They do very well in fish-only communities though, provided their tankmates are reasonably robust and tolerant of these hyperactive, sometimes aggressive fish.

Diet

In the wild Monos feed on zooplankton and small animals including fish and crustaceans. They prefer a meaty diet, but quickly learn to take flake and pellets. Generally good eaters in aquaria.

Social Behaviour

Monos can be troublesome in terms of social behaviour. Wild fish are gregarious as adults though apparently less so when young. However, in aquaria the reverse is often the case, with juveniles schooling nicely but adults becoming belligerent towards one another. Some authors have put this down to reproductive behaviour, suggesting that aggression is related to the broodcare offered by spawning pairs to their eggs. Be that as it may, Monos are best kept in reasonably large groups so that any aggression is diluted. Adults can be kept singly, though they tend to be a bit nervous. Try to keep three or more specimens, ideally mixed with another species of Mono, or better still, a few Scats. This approach seems to work well and prevents any one fish from becoming too dominant.

Monos usually ignore tankmates too large to eat, and work well with Scats, Archerfish, and other reasonably large community species.

Breeding

Monos are said to spawn in freshwater, but beyond that the data are fragmentary and contradictory. Reports of spawning under aquarium conditions are known, but successful rearing of the fry has not yet been accomplished. No differences between the sexes are known.

Species

By far the most commonly traded species is the Common Mono or Malayan Angel Monodactylus argenteus. This species has a round, silver body marked with think vertical bands and prominent yellow patches across the tips of the dorsal and anal fins. Maximum size in the wild is over 20 cm/8", but aquarium specimens are typically only 12-15 cm/5-6" in length.

Less often seen is the West African Mono Monodactylus sebae. This species is very similar to a freshwater Angelfish in shape, being taller than it is long. The body is more rhomboid than circular. It lacks the yellow patches of the Common Mono, and whereas the pelvic fins on the Common Mono are merely very small, on the West African Mono the pelvic fins are completely absent. The West African Mono has four thin vertical black bands: one through the eye, two down the dorsal and anal fins, and the fourth on the caudal peduncle. Maximum length is 25 cm/10" in the wild, but aquarium specimens are much smaller, rarely more than 15 cm/6" long.

The Dwarf Mono Monodactylus kottelati is very similar to Monodactylus argenteus in overall appearance and the two specimens may well be trade under the Common Mono name throughout the hobby. But it is a distinct species said to have a maximum size of less than 8 cm/3.25", making it a prime choice for the home aquarium. The key differences in terms of morphology are the shape and colour of the fins. Compared with the Common Mono, Monodactylus kottelati is a bit taller relative to its length and the fins are more orange than yellow.