On Dither Fish

(This article was originally published in Freshwater and Marine Aquarium Magazine, Nov 1979; pp. 30-34, 76-79. It is here reproduced with the permission of author Dr. Paul V. Loiselle).

"With a little common sense to their selection, representatives of other fish families are not only compatible and aesthetically pleasing additions to a cichlid aquarium, but highly beneficial to the well-being of its inhabitants"

One of the biggest surprises the novice cichlids fancier is apt to encounter in the initial stages of his infatuation is that, despite their reputation for unbridled bellicosity, his pets are frequently less than outgoing when placed in novel surroundings. This extreme timidity is understandable enough in dwarf cichlids, which must cope with an environment richly endowed with larger fishes, most sporting capacious jaws filled with sharp teeth. It is less understandable when seen in a newly acquired Nandopsis managuense, who devotes its waking hours to efforts aimed at insinuating as much of its 25.0 cm length under or behind any available cover. Bear in mind, however, that though such guapotes are the largest predatory fishes in their environment, they are still not immune from predation. Piscivorous reptiles, such as caimans and snakes, a wide gamut of fish-eating birds, among them herons and ospreys, and even such mammalian predators as jaguars and otters, consider these large predatory cichlids as toothsome a meal as do fishermen. When attention to overhead shadows can spell the difference between life and death for the largest cichlids, timidity in new surroundings is not as behaviorally aberrant as one might otherwise think. And as other, more interesting kinds of behavior will not be manifested until such animals feel themselves secure from the threat of predation, the problem of providing them with what they perceive to be safe surroundings is of central concern to the cichlid fancier.

A measure frequently taken by aquarists faced with a reclusive fish is to remove all available hiding places on the grounds that, without cover, the animal will be forced to stay in the open where it can be seen. As is often the case when one is faced with the need to modify undesirable behavior, the most obvious remedy is the least desirable one. An animal deprived of a place to hide has only one course of action open to it when faced with a perceived threat - flight. Under aquarium conditions, frantic efforts at escape eventually result in dead fish. Very large animals can literally "brain" themselves in a frantic effort to swim through a tank wall, but most practitioners of the great escape wind up as fish chips scattered over the floor surrounding their former quarters. Regardless of the risk of losing fish in this manner, it is inhumane to deprive any animal of an element it regards as critical to its well-being, and totally naive to expect normal behavior in its absence. The objective of eliciting a broad spectrum of behavior from captive cichlids is attained not by depriving them of shelter but, rather, by persuading them that continual recourse to such hiding places is not a prerequisite to survival. This is accomplished by creating what the fish perceive as a secure environment. The remainder of this article will consider techniques that have proven successful in attaining this goal.

As I mentioned earlier, cichlids are very sensitive to any sort of overhead movement. Very often the height at which a tank is placed is responsible for the timidity of its inhabitants. Fish housed in waist-level tanks are often excessively retiring and easily frightened by the approach of an observer. Such behavior almost always disappears, or is greatly minimized, if the same tank is resituated at chest, or head, level. The difference in behavior is due to the fact that human activity around an aquarium produces less perceived overhead movement and casts fewer shadows at chest level or higher. Another very simple way of reducing the impact of these extremely powerful fear-inducing stimuli is to provide a cichlid aquarium with a screen of floating plants, the thicker the better. Floating fern (Ceratopteris sp.) is a popular choice, but hornwort (CeratophyEEum sp.) or even duckweed (Lemna sp.) will do quite nicely.

Ignorance of the social behavior of a given cichlid species under natural conditions can also be a factor contributing to its excessive shyness in captivity. When not sexually active, many cichlid species are highly social animals. Such fishes often feel extremely insecure unless housed in groups. Angelfish (Pterophyllum spp.) exemplify this phenomenon. A single pair of young angelfish will spend most of their time in the plants. A group of six to twelve individuals will cruise placidly about in the open and greet their keeper's approach by begging at the surface for food. An appreciation of the density at which cichlids live in nature can be useful in eliciting normal social interactions even when one is dealing with non-schooling species such as mbuna. A single pair, or trio, of any mbuna species will vanish into the rockwork of a 200 1 aquarium, to emerge only at feeding time. Eight to ten individuals, be they of one species or several, in the same aquarium will present a constant montage of interactions in its open spaces.

Even with careful attention to these factors, one may still find that many cichlids continue to behave like the combatants in a guerilla war, carrying on a wide range of activities up to and including spawning, out of their keeper's sight. If such reticence to bare the details of their life histories is annoying to hobbyists, it is disastrous to scientists who wish to study cichlid behavior. It is, thus, no coincidence that behavioral researchers have developed yet another technique to bring timid cichlids out into the open.

First explicitly expounded in 1967 by Dr. G.W. Barlow, the technique takes advantage of the fact that, like many other animals, cichlids are capable of using the behavior of other species as an indicator of environmental security. This is a common enough a phenomenon in nature. One thinks of the sensitivity of deer and other mammals to the alarm calls of jays and crows. In the present case, a group of an open-water, schooling fish is introduced into the tank containing timid cichlids. Such species rely upon schooling as an anti-predator device and will swim contentedly about in the open as long as a certain number of individuals are present. This, in itself, will usually pull hidden cichlids out into the open, while the rapidity with which these schooling species learn to associate the appearance of their keeper with that of food greatly accelerates the process by which the cichlids habituate to the presence of an observer.

	While all Colossoma species grow too large as adults to be confortably housed in home aquaria, young specimens such as this red-breasted pacu make superb dither for large cichlids.
	The cardinal tetra, Paracheirodon axelrodi, is one of the most colorful and popular of the multitude of small characins whose active schooling behaviour recommends them for use as dither fish. In order to be seen at their best, as well as to perform effectively as dither, these highly social fishes must be kept in groups of at least half a dozen.
	Alestes longipinnis, African long-finned tetra, male in the foreground, female to the rear. This vivacious and hardy characoid is an excellent dither fish for the West African dwarf cichlid whose biotope it shares.
	Hemiodopsis semitaeniatus is an excellent dither fish for medium-sized Cichlids. Like all members of the genus, it is a powerful and adroit jumper whose quarters should be tightly covered to prevent its premature demise.
	The smaller plant spawning species of the genus Aphyosemion, such as Aphyosemion celiae, are excellent dither for the smaller Neotropical dwarf cichlids. Though not schooling fish, they are quite active and soon learn to associate their keeper with the arrival of food, behaviour the cichlids quickly come to emulate.
	While not strictly tropical in origin, the bitterlings of the genus Rhodeus are as suitable for use as dither fish as are the more commonly encountered members of the family Cyprinidae. As this male Tanago or Japanese bitterling Rhodeus ocellatus, amply illustrates, these unusual minnows are beautiful aquarium residents in their own right.
	Xenotoca eiseni, the red tailed goodeid, is one of the most colorful and generally available representatives of this distinctive family of Mexican endemics. These unsual livebearers differ from poeciliids in requiring a fresh mating for each brood produced and in being rather scrappier in their behaviour towards other fish. They make excellent dither for the various rock-dwelling Tanganyikan cichlids.
	Like all of its congeners, the dwarf gourami, Colisa lalia, doubles effectively as dither and target fish for the smaller dwarf cichlids.
	The red paradisefish, Macropodus opercularis, is large and aggressive enough to hold its own as a dither fish for both the more aggressive dwarf cichlids, such as Nannacara anomala, and medium sized cichlids such as the smaller Cichlasoma and medium sized Aequidens species. Like the majority of Cyprinodonts, Belontiids are not schooling fish, but their behaviour is still sufficiently extroverted to make them effective dither fish.
	Like all their congeners, female Brachyraphis rhabdophora are quite aggressive towards their smaller consorts, behaviour which often carries over to other species as well. These larger (females up to 10.0 cm SL) voracious poeciliids make excellent dither for some of the larger Tanganyikan Lamprologus species, whose behaviour towards other fish is also unlikely to recommend them for a Nobel Peace Prize.
	The short-finned mollies of the Poecilia sphenops complex, represented by this Green shimmer molly, Poecilia gracilis, are large fast enough to make good dither fish for medium-sized cichlids. Like all mollies, these are prolific breeders, whose fecundity may prove mixed blessing if they are used as dither for cichlids with poorly developed piscivorous abilities.

When highly social species are used in this manner, they are referred to as dither fish. Having introduced the term, I feel the time appropriate to correct an error in its usage that many cichlid enthusiasts, myself among them, have perpetrated over the past decade. As Conrad Lorenz (1952) observed, the likelihood of damaging or lethal conflict between the male and female of a single pair of substratum-spawning cichlids is greatly reduced if other fish are present towards which they can direct aggressive behavior. Pair bond formation also occurs more swiftly and entails reduced risk of injury to the potential partners if such target fish are present. This is the reason why it is widely recommended that such cichlids be allowed to grow to maturity in groups of 6 to 8 individuals. The traditional explanation for the facile paring that occurs under such conditions is that each fish has a wider selection of potential mates and thus an augmented chance of finding a compatible mate. The real reason lies in the presence of numerous targets for the aggression that results when two territorial animals find themselves sharing the same restricted piece of real estate. Many aquarists, when discussing the problem of eliciting successful reproductive behavior from substratum-spawning cichlids, have used the term dither fish to describe such target animals.

The consequences of conflating these two techniques of behavioral manipulation are more than merely semantic. The best target fishes are species perceived as competitors for available spawning sites by a pair of cichlids. By no coincidence, these are either conspecifics or else very closely related cichlid species. The best dither fish are highly social, open-water species whose behavior, while it may result in their being perceived as potential fry predators, is hardly apt to impress a potential breeding pair of cichlids with their potential as spawning site competitors. An additional practical difference in how to best utilize dither and target fishes must also be considered. Dither fish customarily share quarters and are allowed to interact freely with their cichlid neighbors. Unless the aquarium in question is very large or the species being bred is very inoffensive, unrestricted interaction between target fish and the breeding pair is unlikely to result in enhanced life expectancy for the former. Prudence, therefore, dictates allowing target fish to exercise their beneficial influence from the other side of some sort of barrier. Either a glass partition or a screen will do quite nicely, as it is only necessary that the pair see the object of their animus. Actually performing mayhem upon its person, or persons, though possibly cathartic in nature, is not necessary to assure positive results.

This necessary discussion concluded, let us return to the question of selecting appropriate dither fish and using them to best advantage. The first and obvious requirement of any species considered as dither is that it be extroverted in behavior. As I indicated earlier, open-water schooling species such as characoids and cyprinids are the traditional dither fish, but a perusal of Table 1 will reveal that even non-schooling species can serve as effective dither. Whatever species chosen, follow the Table's suggestions as to the number of individuals to be employed. The extroverted behavior of these species will not be apparent unless a certain critical number of individuals are present. Two lemon tetras hiding in the foliage are not likely to provide much reassurance to a group of timid dwarf cichlids, but a dozen individuals schooling in the open will.

A second obvious requirement is that the water chemistry requirements of both dither and subject fish be compatible. For example, while most poeciliids have the necessary behavioral qualifications to make excellent dither fish for Neotropical dwarf cichlids, they do not thrive in the neutral to slightly acid, rather soft water that these cichlids prefer. They are far better utilized as dither for Lake Tanganyika cichlids, such as the various Julidochromis and , whose water requirements match more closely their own preferences. Table 1 also summarizes the water chemistry preferences of the main groups of dither fish.

The third criterion is that of behavioral compatibility. Obviously the size discrepancy between dither and subject should not be so great that the latter regard the former as a dietary supplement. One would not, for example, attempt to use cardinal tetras as dither fish for smaller , though medium-sized cyprinids such as the rosy barb, the various short-finned mollies, or the more robust Australian rainbow fishes would fill the bill quite nicely. Nor should one choose dither fish whose behavior is likely to prove intimidating to the subject fish. I would certainly not recommend housing large, aggressive schooling characins such as Exodon paradoxus or the various Astyanax species with the smaller dwarf cichlids. Though quite extroverted and very responsive to their keeper, these characins are so large and active that their presence is more intimidating than reassuring to the cichlids. Even families usually considered to comprise aquaristically innocuous species can spring the occasional nasty surprise, so it pays to invest in careful research on any species contemplated for use as dither. Most poeciliids, to cite an example, are quite unaggressive towards other fish, but females of the Central American genus Brachyraphis are large and aggressive enough to thrash any cichlid of comparable dimensions. A final consideration in the selection of dither fish is the extent to which they are apt to compete with the subject fish at feeding time. Obviously the behavior of both species has a bearing on this. I would have no reservations about using the larger Rasbora and Danio species as dither in a tank containing some of the larger or more aggressive dwarf cichlids such as the various Pelvicachromis species or Nannacara anomala, who are quite well able to look after themselves at feeding time. I would certainly not use these cyprinids with any of the smaller Apistogramma or , who would be hard put to get a fair share of food when these gluttons go into a feeding frenzy at the surface.

The real problem of competition, however, arises once the cichlids have produced free-swimming fry, who require a copious supply of Artemia nauplii to grow and prosper. While there are some real advantages in enhanced parental reliability to be derived by allowing dither fish to remain in the company of breeding cichlids, their numbers should not be so great that they complicate the problem of getting food to the cichlid fry. Live-bearing dither fish pose the biggest difficulties in this regard. Cichlids differ markedly in their efficiency as piscivores. While the smaller Cichlasoma and Lamprologus species and even Nannacara anomala will exert a powerful check upon the natural increase of any live-bearing fish domiciled with them, many of the other cichlids that benefit from dither are inept predators, quite incapable of making serious inroads into a burgeoning poeciliid or goodeid population. Unless the aquarist intervenes directly to bring dither fish numbers into line, their population will increase to the point where rearing cichlid fry in the same tank becomes impossible, due to the problem of getting sufficient food past superabundance of dither fish. This tendency to over-populate an aquarium is probably the most serious charge that can be leveled against Girardinus metallicus, a beautiful Cuban poeciliid whose modest size and tolerance is soft, acid water otherwise makes it an ideal dither fish for most Neotropical and West African dwarf cichlids.

I frequently hear salespersons in tropical fish shops advise customers against purchasing cichlids on the grounds that they cannot be kept with other kinds of fish. Hopefully, this article will put this fallacy to rest. With a little common sense to their selection, representatives of other fish families are not only compatible and aesthetically pleasing additions to a cichlid aquarium, but highly beneficial to the well-being of its inhabitants as well.

Literature Cited

• Barlow, G.W., 1967. Dither - a way to reduce undesirable fright behavior in ethological studies. Z. Tierpsychol. 25: 315 - 318.
• Lorenz, K.I., 1952. King Solomon's Ring. Methuen, London, xii + 202 pp.

Table I: Synopsis of some Suitable Dither Fish

Family	Representative Genera	Water Chemistry	Mimimum Specification
Alestidae	Alestes, Phenacorammus, Arnolidichthys	pH 5.5-7.2, hardness to 100 ppm TDS	6-8 individuals
	Comments: Large, rather active, predominately surface-feeding characoids. Very effective as dither for West African dwarf cichlids (e.g., Pelvicachromis and Nanochromis spp.) and medium sized Neotropical cichlids such as the shyer Aequidens spp.
Characidae	Cheirodon, Paracheirodon, Hemigrammus, Hyphessobrycon, Moenkhausia, Nematobrycon	pH 5.5-7.2, hardness to 100, ppm TDS	6-8 individuals Nematobrycon sp. Best kept on a harem basis, with one male/tank.
	Comments: Small to medium sized, mainly mid-water feeding characoids. Excellent dither for both Neotropical and West African dwarf cichlids. Larger species (e.g., Hemigrammus caudovittatus, Moenkhausia oligolepis) can be used with medium sized Aequidens spp. and the smaller Cichlasoma spp.
Serrasalmidae Hemiodontidae	Metynnis, Mylopus, Mylasomma, Colossoma Hemiodopsis	pH 5.5-7.8, hardness to 200.0 ppm TDS	4-6 individuals
	Comments: Medium sized to large, more or less strongly herbivorous characoids. Active swimmers in the middle regions of the water column. Excellent dither for such medium sized to large Neoptropical cichlid genera as Aequidens, Geophagus, Cichlasoma, Pterophyllum, Symphysodon and Uaru.
Cyprinidae	Barbus, Brachydanio, Danio, Notropis, Rasbora, Rhodeus, Tanichthys	Most of the genera listed prosper over a pH range of 6.0-7.8, hardness to 200.0 ppm TDS. Some Rasbora spp. have the same requirements as the characins listed above.	4-6 individuals of the larger species, 6 or more of the smaller species (e.g., Tunichthys, Brachydanio)
	Comments: Brachydanio, Danio, Rasbora, and Tanichthys are mid-water living species that feed mainly from the surface. Barbus and Rhodeus typically swim in the lower third of the water column and take much of their food from the bottom. They are thus more af>t to interact with cichlids than any of the genera thus far listed. Notropis comprises both surface/mid-water and mid-water/bottom feeding species. Given the size range of cyprinids, it is possible to find within the family suitable dither for any cichlids.
Cyprinodontidae	Aphyosemion, Aplocheilus, Fundulus, Lucania, Pachypanchax Roloffia Rivulus	Most species prosper over a pH range of 5.5-7.2, hardness to 100.0 ppm. A few Aphyosemion, most Fundulus and Pachypanchax do well in water up to200.0 ppm TDS.	4-6 individuals. Lucania should be treated as one cyprinids or characoids. All would small others best kept on a harem basis, w/ one male/tank, though the smaller Aphyosemion and Rivulus spp. are a partial exception to this rule.
	Comments: With the exception of Lucania, a mid-water swimming, schooling killifish genus, all the genera listed are surface feeders with only a rudimentary social cohesion. The majority of species spawn continuously, prefering sides near the surface. Some Aphyosemion, Roloffia and Fundulus prefer to spawn near the bottom, which increases the probability of aggressive encounters with cichlids. The larger Aplocheilus, Aphyosemion and Rologia are aggressive and predatory enough to pose a threat to the smaller dwarf cichlids and should not be used as dither in their tanks.
Poeciliidae	Brachyraphis, Girardinus, Heterandria, Phallichthys, Poecilia, Priapella, Xiphophorus	Most species prosper over a pH range of 7.0-8.0, hardness to 250.0 ppm TDS. Girardinus and Heterandria will do well in water as acidic as pH 6.0.	4-6 individuals of the larger species (e.g., Brachyraphis, Poecilia, sub-genera Limia and Mollienesiaand Xiphophorus), 6 or more of the smaller species. The larger Poecilia and Xiphophorus species best kept as harems, with only one male/tank.
	Comments: Active, loosely schooling fishes that move throughout the water column. Because of their ability to live in soft, somewhat acid water, Heterandria and Girardinus are excellent dither for West African and Neotropical dwarf cichlids. Other poeciliids are excellent dither for Etroplus spp., the various Lake Tanganyika rock-dwelling cichlids and the smaller Cichlasoma spp. Female Brachyraphis are very aggressive towards their much smaller consorts and towards other fish. They should be used as dither only for cichlids of the same size or slightly larger. Breed continuously so human intervention may be required to keep their numbers within acceptable limits.
Goodeidae	Ameca, Characadon, Xenotoca	pH 7.0-8.0, hardness to 250.0 ppm TDS.	4-6 individuals
	Comments: Similar in most respects to poeciliids in social organization, but overall, slightly more aggresive towards other fish. Males usually more tolerant of one another than is the case with poeciliids of the same size. Excellent dither for most Lake Tanganyika cichlids and the smaller Cichlasoma spp.
Melanotaeniidae	Melanotaenia, Nematocenris	pH 6.5-7.8, hardness to 250.0, ppm TDS.	4-6 individuals
	Comments: Very active, mid-water swimming schooling fishes. Can be used in the same way as Cyprinid species. Large species (e.g., Nematocenris spp.) excellent dither for medium sized to large Cichlasoma spp.
Atherinidae	Pseudomugi, Telmatherina, Bedotia	As for Melanotaeniidae, save that Telmatherina does best in hard, alkaline water containing some NaC1	4-6 individuals
	Comments: Very similar to melanotaeniids in behaviour. Telmatherina an excellent dither fish for the smaller Lake Tanganyika cichlids. Pseudomugil and Bedotia are a good choice of dither for West African dwarf cichlids.
Belontiidae	Colisa, Macropodus, Trichogaster, Trichopsis	pH 6.5-7.8, hardness to 250.0 ppm TDS	4-6 individuals. Best kept on a harem basis, with only a single male/tank.
	Comments: The relatively large size of these loosely social fishes makes them good target fish as well as dither for dwarf cichlids. Both their size and surface-dwelling tendencies reduce their risk of injury from the parental cichlids. Macropodus and Trichogaster make excellent dither for the more aggressive dwarf cichlids, the medium sized Aequidens spp. and the smaller Cichlasoma spp. The preference of Macropodus cupanus dayi for enclosed nesting sites guarantees a conflict over breeding sites with cave spawning dwarf cichlids. This paradise fish should therefore be excluded as dither for these cichlid spp.