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The dwarf jewel fish, Anomalochromis thomasi (Boulenger 1915)

By , 1997. printer
Published
Paul V Loiselle, 2004

Classification: Species overview, Africa.

Hemichromis thomasi A male Hemichromis thomasi. The profusion of metalic blue spangles that characterizes the color pattern of the dwarf jewel fish is more reminiscent of Neotropical than African dwarf cichlid.Photo by Paul V. Loiselle.
(This article was originally published in Freshwater and Marine Aquarium Magazine, feb 1983; pp. 14-18, 85-92. It is here reproduced with the permission of author Dr. Paul V. Loiselle).
(Editor note: Since Dr. Loiselle wrote this article, the species in question has been reclassified to the genus Anomalochromis, monotypic. 1998).

The tropical fish hobby, more so than many others, is characterized by constant flux. Some types of change are essentially linear, notably the steady increase in sophistication in aquaristic hardware, fish foods and medications. Others are less easily characterized. There has, for instance, certainly been a significant increase in the number of fish species available to aquarists since the beginning of the century. By no stretch of the imagination, however, could one describe this trend as linear. The two world wars saw the loss of many species from the hobby, while novelties usually appear in bursts that correspond to the opening of new collecting sites to commercial activity. The explosive debut of the Malawian cichlids in the mid-1960's exemplifies this phenomenon of episodic growth in the availability of aquarium fishes. Finally, some changes seem as unpredictable as fads in the world of high fashion or popular music. In this category fall changes in the popularity of aquarium fishes.

Hemichromis thomasi female The median spot and intercalary bands are only suggested in this ripe female Hemichromis thomasi. This species is not noted for marked sexual differences in coloration. Mature females of some populations may have a few more red spots in the shoulder regionthan do males but, in general, it is unwise to rely upon such color differences when sexing young fish. Photo by Paul V. Loiselle.

The ups and downs of a given species' career as an aquarium resident fascinate me. In some instances, one can erect plausible hypotheses to explain the waxing or waning fortunes of a peculiar fish or group of fish. The virtual disappearance of Gambusia affinis from the ranks of aquarium fishes is almost certainly due to the availability of more colorful and less aggressively unpleasant poeciliids to aquarists with a fondness for livebearing fishes. The current popularity of many of the larger Neotropical cichlids may, with equal plausibility, be linked with the revolution in aquarium construction that followed the introduction of silicone elastic sealant to the aquarium hobby in the early 1960's. This led to a major breakthrough in tank construction that brought the large aquaria required to successfully maintain these cichlids within the means of the majority of hobbyists, an absolute precondition to any increase in their popularity. However, in many cases, no logical exercise serves to explain a seemingly well-established species' fall from favor or the inability of a promising newcomer to gain widespread popular acceptance. The failure of Hemichromis thomasi to rise to the forefront of popularity among African cichlids is an excellent example of the latter phenomenon.

Hemichromis thomasi made its scientific debut in 1915. Its author, the distinguished ichthyologist G.A. Boulenger, originally placed this diminutive cichlid in the genus Paratilapia, at that time an extremely heterogenous assemblage of African cichlids with few features in common save superficially similar dentition in their jaws and a reduced number of anal fin spines. Paratilapia was critically re-examined by Boulenger's successor at the British Museum, C. Tate Regan. His approach was based upon the study of a broader set of skeletal characteristics than were those of his predecessors. His revision of the African cichlids thus succeeded in correcting many erroneous generic attributions and, overall, certainly led to a more biologically meaningful classification of these fishes than had up to that time been available. Regan (1922) restricted the genus Paratilapia to a single species, p. polleni, endemic to the island of Madagascar. The residue of species was reassigned to other genera, Paratilapia thomasi becoming Pelmatochromis thomasi. Regan's views on the relationships of this species stood unchallenged until Daget (1962), on the basis of dental characteristics, shifted it to the genus Haplochromis. In his revision of the genus Pelmatochromis, Thys (1968a) also expressed the view that P. thomasi was inappropriately classified. He forbore proposing an alternative generic placement, but did suggest that its affinities lay with the genus Hemichromis.

Largely on the strength of Thys' preliminary assessment of its relationships, I included P. thomasi within the scope of the revision of the genus Hemichromis I undertook upon my return from Peace Corps service in West Africa in 1971. I found that P. thomasi is characterized by the distinctive Gothic arch pattern of scale architecture (Figure 3), originally described from the genus Hemichromis (Trewavas, 1973). This distinctive pattern of scale ring development is known to occur only in the hemichromine lineage of cichlids, which comprises the genera Hemichromis and Thysia. While certain elements of the color pattern of P. thomasi are suggestive of that seen in Thysia, the two fish differ from one another in gill raker morphology, pattern of sexual dimorphism and certain aspects of their reproductive behavior. With respect to all three of the foregoing characteristics as well as the anatomy of the pharyngeal region and the major features of its color pattern, P thomasi agrees well with the H. bimaculatus complex within the genus Hemichromis.

Cycloid scale arquitecture among African cichlids Figure 3: The two patterns of Cycloid scale arquitecture found among African cichlids. Only in the genera Hemichromis and Thysia are all the scales sculpted in the Gothic (a) pattern. Drawing by Paul V. Loiselle.

The only obstacle that appears to have prevented earlier workers from recognizing the hemichromine affinities of P. thomasi is the nature of its jaw teeth. The buccal dentition of Hemichromis is unicuspid in toto, while in P. thomasi the teeth of the outermost row have been characterized as bicuspid by most workers, though a more accurate description would be spatulate. Additionally, Hemichromis as originally defined (Peters, 1858) and subsequently understood (Gill, 1862; Boulenger, 1915; Regan, 1922) was characterized by a greatly simplified buccal dentition, comprising a complete outer row of teeth and a single incomplete inner series. In both P. thomasi and P. cerasogaster, another nominal Pelmatochromis regarded as having hemichromine affinities by Thys (1968a), the buccal dentition comprises three to five complete tooth rows in each jaw.

During the course of my research, I discovered that the H. bimaculatus species group was characterized by much more intraspecific variability with regard to dental pattern than had previously been reported. I discovered individuals of several species with either complete inner tooth rows or else a complete inner row on one side of the jaw and no inner teeth on the other (Loiselle, 1979a). If this were not proof enough of the plasticity of this character, I also found that the number of tooth rows increased with age in P. cerasogaster. With pattern of buccal dentition no longer a consistently invariant feature of the genus Hemichromis, the major obstacle to moving P. cerasogaster within its limits was eliminated, and only the aberrant dental morphology of P. thomasi remained to set it apart from the other species of the genus.

In an earlier epoch in the history of cichlid systematics, this would have constituted grounds for describing a new genus to contain the prodigal. I chose not to erect another monotypic cichlid genus because a broader range of variation in the form of the buccal dentition characterizes cichlid taxa. Judged on the basis of other lines of evidence to comprise natural groupings, notably the genera Tilapia (Thys, 1968a,b), LabMoc Aromis (Oliver, 197-13 and Gephyrochromis (Fryer, 1957). Hence the decision to include P. thomasi within the genus Hemichromis (Loiselle, 1974), a change in usage that has only begun to make its way into the aquarium literature (Wilson and Loiseile, 1979; Loiselle, l980). In view of both its correct generic placement and the main feature of its color pattern, the common name of dwarf jewel fish seems eminently suitable for this most diminutive representative of the genus Hemichromis.

Originally described from Sierra leone, Hemichromis thomasi ranges from Guinèe (Daget, 1962) eastward to Liberia (Schultz, 1942), though the precise eastern and western limits of its distribution remain to be determined. This is undoubtedly why the aquaristic debut of this beautiful little cichlid was so long in coming. Though it contains many species of potential interest to aquarists, the West Guinean forest bloc has never supported a focus for the ongoing commercial exportation of aquarium fishes. The many killifish of that region were introduced to the hobby largely through the efforts of European aquarists who devoted vacation time to finding and bringing them back to be enjoyed by their less venturesome compatriots. Sometimes ­ though less frequently than I would like ­ these killifish explorers bring other types of fish back with them as well. It was through the efforts of one such broadminded aquarist, the late Erhard Roloff of Karlsruhe, West Germany, that A. thomasi was initially made available to European aquarists. The current aquarium strain of this species is descended from breeding stock bought back by Roloff from the Kenema district of Sierra Leone in 1962. I know of at least one subsequent importation of this species from Liberia (G. Eckstein, pers. comm.), though at the time of writing, these fish have not yet spawned.

Thysia ansorgii male The serially repeated black spots on the flanks of this male Thysia ansorgii are reminiscent of the color pattern seen in parental A. thomasi. However, this element of the color pattern is behaviorally invariant in Thysia, contrary to the case in the dwarf jewel fish. Photo by Paul V. Loiselle.
Thysia ansorgii female The differences in size, finnage and color pattern between this female T. ansorgii and the male depicted at left are another major point of difference between this cave spawning species and the essentially isomorphic, substratum spawning dwarf jewel fish. Photo by Paul V. Loiselle.

Hemichromis thomasi is typically found in small streams flowing under intact forest cover. Such habitats in West Africa are very similar in their chemical make-up to the "blackwater" creeks of South America. Most fishes indigenous to such soft, acidic waters demand comparable conditions in captivity if they are to survive and breed. The dwarf jewel fish is an agreeable exception to this rule. It will prosper over a pH range of 5.5 to 7.8 in water up to 200.0 ppm TDS hardness. 1n fact, this species seems to grow faster and breed more prolifically in moderately hard, alkaline water. Like all dwarf cichlids, A. thomasi is extremely intolerant of dissolved metabolic wastes. Most problems aquarists have with this species can be traced back to a failure in nitrogen cycle management. Either a regime of frequent partial water changes or the use of chemically active filter media such as PolyFilter® will keep A. thomasi healthy. While hardly a rapids or riffle-dweller, the dwarf jewel fish is somewhat sensitive to low dissolved oxygen levels and does appreciate some sort of water movement. An outside power filter scaled to the volume of their quarters and supplemented with an airstone will satisfy both requirements quite nicely. Hemichromis thomasi can be maintained over a temperature range of 20°-30° , but does best and breeds most freely at its upper end.

The generality of Hemichromis are micropredators with more or less piscivorous tendencies. The dwarf jewel fish represents the extreme position at the "less" end of the spectrum. In a contest to determine the most inept piscivore in the Family Cichlidae, A. thomasi would finish in a dead heat with such paragons of predatory incompetence as Aequidens curviceps, Crenicara filamentosa, and Tanganicodus irsacae. Based on my own observations, this species would starve to death in a tank of guppies! In nature, the dwarf jewel fish feeds on insect larvae, small aquatic crustaceans and stranded terrestrial insects. In captivity, any of the usual live, frozen or prepared foods are eagerly taken. For its size, this species is a surprisingly hearty eater that does best when offered two or three moderate meals daily. Both the rosy background color and the red spotting in the opercular region and on the flanks are sensitive to the availability of the appropriate pigment precursor substances in the diet. The regular inclusion of any of the commercially available color foods on its menu suffices to keep these red markings at an esthetically pleasing level of intensity.

Unlike some of its larger congeners, the dwarf jewel fish will not uproot plants. Even during periods of sexual activity, this species will coexist happily with rooted vegetation. This has earned A. thomasi a good deal of favorable press in Europe, where Leiden-style planted aquaria are very popular with hobbyists. In point of fact, A. thomasi does best in quarters well-supplied with cover. Either rooted plants or a combination of inanimate furnishings and floating plant cover serve the purpose equally well. Hill-Kordan's Eco-Logs® seem to be highly appreciated as tank furnishings by this species. Individuals will frequently bestow their ultimate seal of approval on these well-crafted simulacra by selecting them as spawning sites!

Hemichromis guttatus The main features of the color pattern of this female of the aquarium strain of Hemichromis guttatus are essentially the same as those of A. thomasi. Like other representatives of the H. bimaculatus species complex, the common jewel fish grows larger and has a simpler pattern of jaw teeth than does its diminutive congener, not to mention a considerably more peppery disposition! Photo by Paul V. Loiselle.
Barbus evretti Large cyprinids such as Barbus evretti, the clown barb, are too pushy to make good dither fish for Hemichromis thomasi, though they can fill this office well enough for more assertive cichlids. Photo by Paul V. Loiselle.
Trichogaster leeri The less aggressive labyrinth fishes such as this pearl gourami make excellent companions for A. thomasi. Like Trichogaster leeri, they are usually quite uninhibited in their behavior, while their preference for the upper half of the water column minimizes the risk of confrontation with their bottom oriented cichlid companions. Photo by Paul V. Loiselle.

When not breeding, A. thomasi behaves in an entirely innocuous manner towards other fish. This is a moderately social species that is best kept in small groups, preferably comprising equal numbers of each sex. Like most dwarf cichlids, it is rather retiring in captivity. A generous cover of floating plants and the use of appropriate dither fish (Loiselle, 1979b) will effectively eliminate any undesirable shyness. Large, fast-swimming species such as the giant danio, congo tetra or some of the larger barbs are best avoided when selecting dither fish for A. thomasi. They often outcompete the dwarf jewel fish at feeding time and their boisterous activity may inhibit spawning. The smaller barbs, rasboras and tetras make excellent companions for this cichlid, as do the smaller labryrinth fishes and poeciliids. Provided the aquarium is large enough to satisfy all of their territorial needs, other dwarf cichlids can also be housed with A. thomasi. It is a good idea to scrutinize closely the interactions of such extroverts as Nannacara anomala and Apistogramma cacatuoides with the dwarf jewel fish and separate the participants if there is any sign that the latter are being bullied by their more assertive companions.

The dwarf jewel fish is among the most easily bred African dwarf cichlids. If the fish are kept in groups of six to eight individuals in the manner described above, it is virtually impossible to prevent successful pairing and subsequent spawning. Two or three pairs will partition a 160 l aquarium among themselves with little more than the most ritualized of boundary conflicts. It is equally feasible to set up single pairs in 80 l -100 l tanks. These may seem excessively generous quarters for a fish not known to exceed 8.0 cm SL, but there are valid reasons for providing pairs with this much living space. The female runs some risk of injury from her putative mate if her reproductive cycle should he somewhat out of phase with his. Spacious quarters allow her enough maneuvering room to avoid unwelcome attention until she is able to respond appropriately to the male's advances. Equally important is the need to provide enough space for the fry to grow at a normal rate during their first six to eight weeks of mobile life. The dwarf jewel fish is a remarkably fecund little cichlid. Spawns can number up to 500 eggs and fry survival in the absence of some catastrophic interruption of the normal pattern of brood care is high. A 100 l aquarium is large enough to support such a swarm of fry until they have grown large enough to be easily ­ and safely ­ moved to other quarters.

Hemichromis thomasi will spawn freely under community conditions, but the likelihood of fry surviving to independence under such circumstances is slight. This species appears incapable of deterring nocturnal predation on wrigglers by loaches and catfishes and has a less-than-impressive record of standing off fast-swimming, aggressive day-hunting predators of its mobile fry. Hence the injunction to avoid housing A. thomasi with such companions as the larger characoids and cyprinids. I am at something of a loss to understand how the dwarf jewel fish manages to perpetuate itself in nature, where it is typically collected together with an assortment of potential alestid and cyprinid fry predators, not to mention two, and in some instances, three highly piscivorous congeners! Be that as it may, the only reliably safe dither/target fish for breeding pairs of this cichlid are small cyprinids or characoids.

Target fish are not necessary if the fish are maintained on a group basis. Both neighboring pairs and sexually inactive individuals will supply all the incentive required for a pair to maintain a coherent bond up to the actual spawning act. If the group should contain a surplus of females, there is a very strong possibility that the male of a pair will abandon mate and eggs to take up with a ripe, but unattached, female. There are no data on the occurrence of such polygynous breeding in nature. The consistent failure of abandoned females to bring fry to independence under the considerably more benign conditions of aquarium culture suggests that such male infidelity is an artifact of captivity rather than a manifestation of a naturally occurring alternative to the typical monogamy of hemichromine cichlids. Hence, the injunction to arrange for a balanced sex ratio in groups of prospective breeders.

The spawning behavior of Hemichromis thomasi
Hemichromis thomasi spawning sequence Hemichromis thomasi spawning sequence Hemichromis thomasi spawning sequence
Hemichromis thomasi spawning sequence Hemichromis thomasi spawning sequence Hemichromis thomasi spawning sequence
Hemichromis thomasi spawning sequence Hemichromis thomasi spawning sequence Hemichromis thomasi spawning sequence

The spawning behavior of Hemichromis thomasi is essentially the same as that of other substratum spawning cichlids. Close coordination between the male and female results in a minuscule percentage of eggs failing fertilized. Photos by Paul V. Loiselle.

The dwarf jewel fish prefers to spawn on solid, flat surfaces, such as water-worn stones, halved coconut shells, pieces of driftwood and the ever-popular Eco-Logs®. Though I have not observed such behavior, this species has also been reported to spawn on broad-leafed aquatic plants (, 1970). Very rarely, a pair will dig all the way through the gravel and spawn on the bottom of the breeding tank itself. The spawning site is usually more sheltered in its placement than is the case with the larger Hemichromis species, whose larger size and considerably more bellicose temperament afford them the option of spawning in the open with minimal risk to their progeny. Unlike the related Thysia ansorgii, A. thomasi cannot be described as a cave spawner. The compact, roughly circular plaque of eggs is placed in the open rather than on the walls or roof of a cave. As is the case with other hemichromines, the spawning site is vigorously nipped off prior to oviposition, the bulk of the actual work falling to the female's lot. Some pairs may concurrently begin to excavate shallow depressions in the immediate vicinity of the intended spawning site, but in most instances, such behavior is more characteristic of the immediate post-spawning phase of the reproductive cycle.

Hemichromis thomasi This clutch of eyed fry, placed on one of Kordon Eco-logs, is on the verge of being chewed out of their egg shells by her vigilant mother. Though both parents will trade off duties during the pre-hatching phase of brood care, the female has the chief responsability for keeping the developing zygotes clean and well aerated. Photo by Paul V. Loiselle.
Hemichromis thomasi Both parents pay a good deal of attention to the wrigglers, which may be moved several times before they become free-swimming. Photo by Paul V. Loiselle.
Hemichromis thomasi The mobile fry remain in a compact school for the first week or so of their lives. As they grow older, this tendency is less pronounced, afact which complicates their guardians' task. Photo by Paul V. Loiselle.

The appearance of a blunt, white ovipositor is a certain indicator that spawning will occur sometime within the next 24 hours. The mechanics of spawning, as depicted in the accompanying series of photographs, do not differ significantly from the norm for other substratum-spawning cichlids. Once spawning has been completed, the male is chiefly responsible for perimeter defense, with the female discharging the twin functions of keeping the egg mass clean and well-aerated while deterring any predators that might have eluded the male's vigilance. There is a fair amount of role swapping between the sexes, however, accompanied by the sort of nest-relief ceremony often encountered in Neotropical cichlids (Loiselle, 1982).

The eggs hatch in 48 hours at 25°C. Well prior to this point, the pair will have dug several shallow pits to receive the newly hatched fry. It is common for the wrigglers to be moved several times during the 72 to 80 hours required for them to attain mobility. This species is unusual in that the fry become free-swimming before their yolk-sacs are completely absorbed (Wilson and Loiselle, 1979). The fry exhaust this food reserve 12 to 16 hours after they begin to swim. At this point, feeding should commence. Microworms and the smallest Artemia nauplii are the first foods of choice, to be followed within a week by larger nauplii and finely powdered prepared foods.

Young pairs may eat their first spawns, but usually settle down and become models of cichlid parenthood thereafter. In captivity, brood care typically persists for four weeks. At this point, the female is ready to spawn again, an event whose preliminaries include dispersal of the earlier brood beyond the boundaries of the parental territory. The behavior of other Hemichromis species and Thysia ansorgii in nature, no less than the rather slow growth of the fry themselves suggests that this behavior is also an artifact of captivity. If the aquarist's object is to maximize the output of fry, allowing a pair to respawn so quickly does no harm. However, aquarists wishing to observe a closer facsimile of naturally occurring behavior would do well to discourage the rapid maturation of another clutch of eggs by lowering the temperature in the spawning tank by three or four degrees Celsius once the fry have become fully mobile.

By comparison with other Hemichromis species or, for that matter, other African riverine dwarf cichlids, A. thomasi is a slow-growing fish. Under favorable conditions, fry can attain 1.0 cm TL by the sixth week postspawning, while sexual maturity is rarely attained before the tenth month postspawning, at a length of c. 4.5 cm SL for both sexes. By way of compensation, this is a long-lived little cichlid. Fish up to five years old show no evidence of waning vigor or reproductive arrest (Wilson and Loiselle, 1979).

The great mystery surrounding A. thomasi is its almost total absence from commercial channels of fish supply. Professional breeders are usually unenthusiastic about dwarf cichlids because they are neither sufficiently robust to resist the handling usually afforded fish in a mass-production operation nor sufficiently fecund to economically justify the labor involved in their production. The dwarf jewel fish suffers from neither shortcoming, while its tolerance of hard, alkaline water suggests that it is a promising candidate for large-scale production by fish farmers in Florida, where such conditions are the norm. It is certainly true that large-scale production of a given species usually follows a demand for that fish. Hopefully, this essay will contribute towards creating such a demand and, in so doing, lead to the wider availability of this sparkling representative of Africa's living jewels.

References (18):

Citation

Loiselle, Paul V. (June 19, 1997). "The dwarf jewel fish, Anomalochromis thomasi (Boulenger 1915)". Cichlid Room Companion. Retrieved on October 24, 2017, from: https://www.cichlidae.com/article.php?id=53.