"They eat what? Yee-uck!" Yes, this might well be your first reaction to the family Scatophagidae, "the dung eaters". Their food-choice habits aside though, this small group of fishes make delightful, intelligent marine, and if done correctly, hardy brackish water aquarium specimens.
The principal stumbling blocks to scat husbandry are in order, improper and unstable environment, poor selection of stock, and inadequate feeding. For these and other brackish-sold- as-semi-freshwater livestock (e.g. Monodactylus, mollies, teraponids) I'll offer my views on how to avoid these problems and provide for their long-term care.
Classification: Taxonomy, Relation With Other Groups
Looking at a scat what sort of fish do they resemble to you? With their pan-shaped, laterally-compressed bodies they might easily be mistaken for Butterflyfishes (Chaetodontidae). But glimpse a little further; some differences include scats' deeply notched dorsal fins. Compared with the continuous of slightly notched ones of Butterflies. And the scats lack the Butterflies protractile mouth, though this doesn't slow them down at the chow line.
A further large diverging point is behavior. Whereas chaetodonts are shy and retiring, scats that have been acclimated are the zenith in outgoingness; literally rubbing their faces raw in recognition of their aquarist owners.
Scats are grouped in the same huge Order (Perciformes) as the B/Fs, but in a separate suborder (Acanthuroidei) with other notable marine aquarium families. Spadefishes (Ephippidae), Rabbitfishes (Siganidae), Surgeons/Doctorfishes/tangs (Acanthuridae) and others share structural, developmental plus important dietary and handling characteristics with the scatophagids.
The distribution of Scats is well-documented; they hale principally from Southeast Asia and the Indo-Australian Archipelago in shallow coastal seas all the way to the east coast of Africa. Adults enter into freshwater occasionally to reproduce as where the young may be collected along shallow shores.
Think you've seen big, old scats? They're known to live more than twenty years in captivity & attain plate size. Yep, more than thirty five centimeters (14 inches) in the wild.
In older schemes, the Scats or Butterfishes comprise two genera (Scatophagus, Selenotoca) and four species. According to ICLARM's FishBase, there are four species: Scatophagus argus, Scatophagus multifasciatus, Scatophagus papuensis, Scatophagus tetracanthus. Below are comments to help guide you through the hobby and scientific literature blend.
For nice color pix of these species, please see p. 329 of the Burgess/Axelrod/Hunziker Marine Atlas.
Selection: General to Specific
All the Scats are about the same hardiness/touchiness as individuals and species. I'll go out on a limb and state further that these fishes may be purchased at any size offered, with little difference in their likelihood to adapt and thrive. The real source of losses with scats lies with environment and care.
Be that as it may, there are definite signs to look for, and avoid in choosing specimens; first of all behavioral. Scats are social animals and by and large you should select the most outgoing individual(s). This will be the brightest, most outgoing one(s) in the system, that periodically raise/lower their dorsal spines... and chase the other fish(es) around.
Second in my score card of importance is "index of fitness" or porkiness of the specimen(s). They should be full in appearance, and still looking for food. Don't buy thin Scats! Skinniness is a sign that something is wrong; they've been mis-, underfed, suffered/are suffering from transport/acclimation.
Lastly, the issue of "apparent health" overall; are the eyes clear? They should be. Inter-fin ray membranes intact? These will regrow, and should be okay, or show signs of healing. Are there any signs of lymph (see below under Disease) on any of the specimens in the system? If so, maybe you ought to pass on this batch.
A word of caution when handling scats. Be careful when netting these fishes; their spiny fins easily puncture hands and bags. Some writers list them as venomous, the pain from punctures being so intense. Handle with care.
Ah yes, finally, the area of most concern to aquarists. It is my opinion that the success rate of keeping "brackish water life" is worse than marines, and simply for wont of understanding what all marine aquarists know: the value of optimized, constant water quality.
There has been several fortunes lost in improperly dealing with suitable water quality and brackish organisms in captivity. Part of the reason scats, Monos, Targetfish, Tigerfishes (Datnoides), et al. cost so much is the large incidental losses in their handling through collection to the end-user. And these fishes are decidedly tough; not given to easy dying.
If you would be a Scat keeper, please understand this, these animals are found in fresh(er) water really only as juveniles. As they grow, they make their way down rivers and become marine. They do make forays into fresh to feed and reproduce, and can adapt to less-than totally marine conditions, but their physiology, and more importantly, that of the biological filtration of their system is best suited for a set of standard conditions.
In particular specific gravity and pH should be monitored and adjusted for system and make-up waters. For water density, at least two teaspoons of salt per gallon, (a value of 1.015 is my choice) made from treated tap water and a good synthetic salt mix. They may, of course, be kept in straight seawater.
What the absolute salinity is is not paramount, that it not change a lot (more than a thousandth or so per day) is important. The reasons for this are two-fold; for the osmotic balance of the fishes (and possibly other macro-life), and the metabolic integrity of the microbes that make up the biological filtration. The latter are not able to easily adjust to rapid or extreme changes in salt content, and you know all too well what their loss spells: d.i.s.a.s.t.e.r.
Yes, most "brackish" livestock losses are due to that old aquarium nemesis, ammonia poisoning... most often brought on by fluctuating water quality conditions that suppressed nitrification.
What sort of pH do you think Scats and other brackish water fishes enjoy? Probably something in-between freshwater and marine... mid to upper 7's? You're right. And do you think that with such big, messy eaters and defecators as scats you should be on your guard at buffering the alkalinity against drops in pH? Right again. Many successful brackish system keepers utilize a pinch of baking soda or similar aquarium preparation just for this purpose once a week in conjunction with a partial water change. A calcareous substrate, of at least some aragonite, dolomite, crushed coral... is of great utility.
Temperature is not critical; something steady between 68-82 F (20-28 C) will do.
Though Scats are generally right out front where the action is to catch your attention, they do best in systems that are large (several times they're length), at least three feet long and well decorated. Especially if you're housing more than one individual, they need spaces, crannies between rocks, plants et al. to get out of the sight and way of the alpha fish.
How do we maintain high, consistent good-quality water, with saturated oxygen concentration? With vigorous appropriate filtration. At the very least for brackish water you will want undergravel and outside power filtration. Better still would be an outside, remoted system, the best a marine refugium arrangement with a protein skimmer.
Scats get along with all fishes bigger than their mouths and are generally not bothered by others, with one exception... other scats. Take care to assess the degree of bullying, such that it never goes too far; that scat-tankmates don't get physically beat or starved.
Seeming antithetical to the above, scats are social animals, almost always found in close association with conspecifics, and of endless observable fun in groups in aquariums. If space allows, definitely try a small, odd number of a single or mixed species together.
Rearranging the decor, placing smaller individuals first or all Scats at once, special live food feedings all help to alleviate agonistic behavior when introducing scats.
Use a hydrometer (glass ones in a tall thin (e.g. olive) jar) to test the specific gravity of the water your new fish are in and match this as well as you can in their receiving system, ideally a separate quarantine tank. If the two waters were only a few thousandths difference, and the specimen(s) in good shape, they might do fine just being plunked in "with the rest", but I ask you. Wouldn't it be advisable to allow the new arrivals to rest, harden, and fatten up a bit before taking on the main/display tank? Very likely they were wild-collected days to a few weeks back, and fed little or nothing since. Being debilitated, perhaps they'll fall prey to infection and spread this in your principal show tank.
If you are familiar with dipping procedures for marine livestock, you might consider bathing your new Scat(s). Otherwise, this is not critically important with these fishes.
As stated elsewhere, these fishes are left alone by piscine and human predators; "You are what you eat", makes them very unpalatable.
Likewise they are quite disinterested in most any motile or attached animal, though plants are a different matter (see below).
Reproduction, Sexual Differentiation:
Scats are anadromous, swimming up-stream salmon-wise as it were to reproduce. There are no discernible differences in color, pattern or structure between the sexes. All but the African Scat have been and are bred in captivity through hormonal and environmental manipulation.
Feeding/Foods/Nutrition: Types, Frequency, Amount, Wastes
Despite their unsavory feces-eating appellation scats are mostly herbivorous in the wild, feeding most on algae. In aquariums, they are "hogs of the tank", opportunistic omnivores that will more than gladly eat anything and everything offered. If your Scats won't eat, you've got big problems.
Without a varied, complete and frequently offered diet these fishes will not live up to their potential, growth, color or behavior-wise. They should be fed at least twice a day with some vegetable material always included. This can be store bought or home made, including terrestrial greens which have been softened by microwaving, boiling or freezing.
All other forms of food, live, frozen, freeze-dried, pelleted, extruded, flake... are taken with gusto. Take care that your Scat(s) do not deprive your other livestock of sustenance.
One last suggestion; train yours to accept less expensive foodstuffs early on, as these fishes can literally eat you out of house and home.
Disease: Infectious, Parasitic
Ich and velvet can infect Scats; these scourges are easily defeated with "standard" fish remedies.
A peculiar virally-mediated growth, so frequently encountered with these fishes that it's termed "Scat disease" or lymphocystis is all too common. Lymphocystis, whitish-grayish growths occur most frequently on the origins of fins. There are various treatments sold to "cure" lymph, but I encourage you instead to take your time. This "disease" is generally self-curing and rarely fatal. If the growths seem to be getting much worse or are offensive to you, hand removing them via pinching between finger nails seems to speed up eradication.
Tuberculosis, or wasting disease, has been cited as a problem with Scats, but I have yet to observe runaway cases in an optimized, well-fed set-up.
Various authors have stated that Scats can make do with drastic changes in water chemistry, temperature and biological make-up in their aquariums, even rapid moves in specific gravity. Though Scats are indeed tough (the first ones I ever caught were just off the end of a sewage outfall in Bangkok) this has not been my experience. I would like to re-stress the two most important challenges of keeping these, and many other brackish fishes; adequate feeding and stable salted environment.
Their number one cause of death at aquarists hands is directly tied to environmental instability; too much, too soon change in specific gravity, rapid dropping pH are deadly. Make-up water should be pre-prepared as is done for marine set-ups; adjusted for specific gravity, temperature and pH. Alkaline reserve should be guaranteed by the use of adjuncts and calcareous substrate and/or filter media.
Secondly, for such apparently small fishes, scats need copious amounts of food some of it green.
Given these small considerations you can almost be assured a good, and long close relationships with these brackish-marine fishes.
Armes, Hal E. 1985. A fish for any decor. FAMA 5/85.
Burgess, Warren E., Axelrod, Herbert R. & Raymond E. Hunziker. 1990. Atlas of Aquarium Fishes. V.1, Marines. T.F.H. Publications, NJ.
Eisenburg, Thomas. Undated. The greedy but loving argus fish from southeast Asia. ADI #37, p. 22.
Fenner, Robert. 1996. Scats: Aquatic vacuum cleaners. TFH 11/96.
Morgan, Steve. 1983. Scats... personable, hardy garbage disposals for the brackish water aquarium. TFH 4/83.
Nelson, Joseph S. 1994. Fishes of the World, 3d ed. Wiley & Sons, Inc. NY.