Cichlid Room Companion


Heckel's Thread-Finned Acara Acarichthys heckelii (Mueller and Troschel 1848)

By , 1997. printer
Wayne Leibel, 2003

Classification: Species overview, South America.

(This article was originally published in Freshwater and Marine Aquarium Magazine, Jan 1984; pp. 15-19, 78-86. It is here reproduced with the permission of author Dr. Wayne S. Leibel).
(Editor Note by Juan Miguel Artigas Azas: The present article as originally appeared, included some genera names no longer in use due to taxonomy evolution. In an attempt to avoid confusion and take advantage of the possibility of updating electronic publications in the WWW, I have updated in this article the genera name of some of the species mentioned in this paper to reflect their current status, jul-97).
Acarichthys heckelii

Figure 1: Mature female Basketmouth Cichlid, Acaronia nassa (5.5 inch TL). Photo by Wayne S. Leibel.


Acarichthys heckelii (Muller and Troschel 1848) is, without doubt, one of the most attractive and sought after members of the neotropical geophagine cichlid assemblage. Although sporadically imported for many years and adjusting easily and well to aquarium life, Acarichthys heckelii had, until recently, resisted attempts to elicit reproduction in captivity. Baran (1981) reported perhaps the first viable spawning of this fish in the hobby literature. This article describes a second such eventful spawning and, in general, the biology of this magnificent cichlid.

Taxonomic History and Status of Acarichthys heckelii

Acarichthys heckelii was first described by Muller and Troschel (1848) as Acara heckelii from material collected in Guyana and later installed by Eigenmann (1912) in the monotypic genus Acarichthys. Eigenmann erected this genus for Aequidens-like fishes with feebly developed epibranchial lobes and few (1-2) rakers along the margin of the first gill arch: the former characteristic separating Acarichthys from Aequidens Eigenmann and Bray 1894 (no lobe) and from Geophagus Heckel 1840 (well-developed lobe), and the latter differing dramatically from species of the genus Geophagus (10 or more long thin rakers) and more like species of the genus Aequidens in number and size (a few, short, stout rakers). The apparent transitional position of Acarichthys heckelii between the genera Aequidens and Geophagus is reflected by the nomenclatural history of this fish. Acara (=Aequidens) subocularis (Cope 1878) and Geophagus thayeri Steindachner 1875 were first synonymized by Regan (1905) under the former nomen on the basis of "thayeri's" reduced gill lobe-raker structure. The invalid name Geophagus thayeri is still erroneously applied in the aquarium trade to both Acarichthys heckelii and Geophagus surinamensis (Bloch 1791) perhaps due to its unfortunate published validation by Axelrod (et. al 1962), in an earlier edition of his "Exotic Tropical Fishes," an error later corrected in a subsequent revision (Revised and Expanded Edition, 1980). Both nomen have been subsequently proven junior synonyms of Acara heckelii Muller and Troschel 1848 and consequently reclassified by Eigenmann (1912) in the genus Acarichthys.

Pellegrin (1903) first mentioned the peculiar lobe-raker morphology of Geophagus thayeri Steindachner 1875 and suggested that it might be an intermediate species form bridging the genera Acara (=Aequidens) and Geophagus. Eigenmann (1912) later amplified this position in his description of the new genus Acarichthys. He writes: "This genus bridges the gap between Aequidens on the one side and Geophagus on the other" (page 500).

Lowe-McConnell (1969) writes anecdotally that the native Guyanan fisherman refer to Acarichthys heckelii alternately as 'Shau,' the native name for Geophagus species, or 'Deburus,' the name for Aequidens species. While Steindachner (1875) and Cope (1878) both noted a superficial resemblance between Acarichthys heckelii and Biotodoma cupido (Heckel 1840), Eigenmann (1912) suggests a close relationship to the genus Retroculus (Castelnau 1855; a genus with similar gill lobe-raker morphology) and further notes, "It approaches Guianacara geayi very closely in shape (page 500)." (See Loiselle 1980 for photographs of the above geophagine fish.) More recent study has supported this implied evolutionary relatedness with Guianacara geayi which occurs sympatrically with Acarichthys heckelii in the Guyana portion of its distribution. Regan (1905) first articulated this position directly. He writes: "Consequently this species falls in the genus Acara and there can be no doubt that its position is next to Acara geayi Pellegrin which it resembles in many respects" (page 557). Adults of the two species and especially juveniles under 2 cm Total Length (TL) (see below) bear a strong resemblance to each other (Figures 7 & 8). Kullander (1980) has recently that Guianacara geayi be removed from the genus Aequidens and lumped with heckelii in the genus Acarichthys, a suggestion already adopted by some German aquarists (Baran 1981) prior to official reclassification.

General Appearance

Acarichthys heckelii is an exceedingly attractive medium-sized cichlid reaching standard lengths of nearly 150 mm in the aquarium, this in contrast to Cichocki's (1976) reported maximum of 120 mm SL for wild specimens. The body is chunky and definitely not geophagine in profile: the mouth is smaller, only moderately protrusible, and located centrally in the head, in contrast to the large, underslung mouth and corresponding long-nosed flat ventral profile of typical geophagine cichlids like Satanoperca jurupari. While the peculiar gill morphology (few gill rakers) precludes extensive substrate sifting, Acarichthys heckelii is an amazing digger in the aquarium and in the wild (see "Reproductive Habits"). Not surprisingly, Acarichthys heckelii is a mid-water fish taking food from all regions of the water column, in contrast to the more substrate-oriented habits of Satanoperca jurupari, for example.

The base color of this fish is a medium green-gray with a series of indistinct pentagonal or hexagonal splotches scattered regularly over the body; a "camouflage" pattern which is expressed darkly and distinctly in juveniles and submissive adults. A coppery-orange saddle extends from the opercular margin backwards to the dark mid-lateral blotch and from the dorsal fin insertion downwards nearly to the ventrum. The flanks are overlain with parallel rows of brassy lines formed by the iridescent centers of each scale, a pattern strongly reminiscent of Satanoperca jurupari. A large (eye-sized) black mid-lateral blotch is flanked immediately front and rear by hight (copper-white) bars reminiscent of Biotodoma cupido. These are usually indistinct, but become prominent when the black blotch fades in submissive individuals. A black bar extends from the eye downward on the operculum (like Guianacara geayi) and these are only faintly connected interorbitally. The opercula are lightly spotted in blue and the gill membranes (branchiostegals) darken to jet black during courtship and spawning.

The first 2-3 rays of the spiny dorsal are black, particularly in fry and juveniles (Figure 6). This color fades in adults but is expressed during courtship. The intermembranes of the soft dorsal are spotted in hyaline white and 5-6 branched soft rays are spectacularly produced and tipped in bright red, sweeping back past the caudal in fine specimens (see Figure 1). The caudal is slightly to moderately emarginate, tipped with small red filaments on its upper and lower margins, and with rows of intermembranous hyaline spots like the dorsal. The anal is bright orange with blue dots, well produced, and edged in dark red and black. The ventrals are feathered and are of moderate length, bright orange, and edged in black (first ray) which darkens during courtship and spawning. I would propose the common sobriquet: "Heckel's Thread-Finned Acara" on the basis of this spectacular, filamentous finnage.

Although Cichocki (1976) suggests that the length of the soft dorsal filaments and body size (male larger than female) are reliable dimorphic characters, the only obvious and consistent sexual dimorphism I have noted in my breeding individuals is body shape. Ripe females are noticeably rounded and the steep angle of the roe-filled abdomen creates the illusion of an iridescent splotch just above the genital pore (Figure 2). The forehead of the male is conspicuously straighter and steeper, and gives his face a more compressed, pug-nosed look. Sexing is quite easy during the last stages of courtship when the female's huge ovipositor is extruded and carried almost horizontal and parallel to her ventrum. High temperatures (85-90°F) reliably elicit courtship and spawning tube extrusion in these fish (see Inducing Reproduction below) and may be used to sex adults.

Biotype and Natural History

Biogeography: Acarichthys heckelii has been seined from ponds and rivers in the Essequibo drainage of Guyana and the northern Amazonian River system from Peru eastward into Brazil (Eigenmann 1912, Lowe-McConnell 1969). A most complete study of their natural history in the Rupununi River district of Guyana (southern tributary of the Essequibo River) has been accomplished and published by Fred Cichocki (1976). It is this work that provides most of what is currently known about the natural history and reproductive behavior of this animal.

I was greeted one morning with the badly mauled corpse-to-be of the female

In the Rupununi River district, Acarichthys heckelii is found in both permanent, spring-fed shallow (2 meter) ponds over a mixed silica sand ­ compact peat bottom, and in typical adjoining riverine environments and their seasonal overflow impoundments in the adjacent Savannah. In general, water in these permanent points was soft and acid (pH = 6.00-6.75), but other populations of Acarichthys heckelii were found living in neutral to alkaline water (pH = 7-8) with moderate carbonate hardness (Cichocki 1976). This apparent wide tolerance for water chemistry is mirrored by experience in the aquarium where captive heckelii are quite adaptive. The mean April to July (wet season) temperature of these various biotypes ranged from 28-30.5°C (82.5-87°F) for the year 1971 (Cichocki 1976), close to the annual average daily air temperature of 28 + 6°C (82 + 11°F) reported previously for this area by Lowe-McConnell (1964). With exceptions noted by Cichocki (1976), the pool and riverine waters are generally clear which, together with the general softness and acidity of the water, reflect the relatively poor mineral content of the soil (Lowe-McConnell 1964).

Reproductive Behavior: Having read Loiselle's (1980) offhand statement that Acarichthys heckelii is "a biparently substratum (spawner) which deposits its clutch inside of a long burrow dug into the substratum" (page 24), I was not prepared for Cichocki's (1976) fuller account of this peculiar reproductive mode based on hours of mask and snorkel observation of numerous pairs in Grani Pond (Guyana). The pond is a permanent spring-fed pond of about 2 meter maximum depth with a silica sand bottom covered in the center by a thick solid layer of black earthy peat. Although juvenile and non-breeding adults frequent the vegetated periphery of the pond, breeding adults set up housekeeping only in the unvegetated, peat-covered central areas of the pond.

Females compete for territories and dig burrows or tunnels down into the peaty bottom. Cichocki (1976) describes these as having almost vertical entry shafts which grade into horizontal tunnels of 13-53 cm length which lead to a larger, central nuptial chamber where the eggs will actually be laid. There may be several openings to this nuptial chamber and several blind side chambers: the entire arrangement is strangely reminiscent of gopher excavations. Once the complex has been excavated, ripe resident females actively solicit male consorts who happen by. Once a suitable mate is selected, the pair defends a territory of 2-3 meters diameter above the peat substrate with the area over the nuptial chamber as the focal point. Following a protracted courtship whose behavioral components have been exhaustively detailed by Cichocki (1976) nearly 2000 eggs are laid, presumably on the walls and roof of the nuptial chamber. Fanning the clutch is primarily the responsibility of the female, while the male actively patrols the territory above the nest-tunnel complex. Following hatching and free-swimming stages, the parents continue to guard their fry using the nest as the focal point. When endangered, the fry pour back into the burrow in response to parental signaling. The fry are abandoned by their parents at 8-12 mm SL, but may continue to stay near the nest and use it for escape in the absence of the parents. Once vacated, the burrow may be claimed by another ripe female, and the reproductive cycle repeated. Given the solid compact consistency of the peat, the burrows may be re-used many times. Although Lowe-McConnell (1969) suggested that Acarichthys heckelii was probably a seasonal spawner, Cichocki (1976) found neither seasonality nor synchrony to gonadal ripening and reproduction. Sexual maturity is apparently reached in the second physiological year at a mean Standard Length (SL) of 65 mm for females, and in the third physiological year for males at a mean SL of 75 mm: most of the spawnings witnessed by Cichocki (1976) involved individuals of at least two full years of age. My own breeders had been raised for just under one year from a pool of 60 mm SL individuals and were probably two years old when they spawned (see below).

General Maintenance and Reproduction in Captivity

Acarichthys heckelii
Figure 2:Ripe pair of Acarichthys Heckelii courting. Note rounded adbomen of roe-filled female. Photo by Wayne S. Leibel.

Acarichthys heckelii

Figure 3: Ripe pairs of Acarichthys heckelii exibiting threat behavior over a territoral marker. The female is the heavier fish in each pair.Photo by Wayne S. Leibel.

General Maintenance: Cichocki's (1976) data provide a good basis for successful maintenance and propagation strategy. In general, Acarichthys heckelii presents no problem in maintenance. I have found them to be rather insensitive to water chemistry or condition (nitrogen cycle maintenance). They are omnivorous and voracious feeders taking all flake, pelleted, frozen, and live foods with considerable and equivalent relish. The inclusion of some vegetable material is advisable on the strength of gut analyses reported by Lowe-McConnell (1969) and by my own experience. In general, Acarichthys heckelii prefers warmer temperatures (at least 80°F), but is quite tolerant of temperatures ranging from the mid-60's to high-90°s (°F; see below).

The fish does have two serious drawbacks as an aquarium citizen: they are tremendous and incessant gravel movers, and the adults are unpredictably vicious towards conspecifics. The former is not a problem for me: I keep all of my geophagine cichlids in plantless tanks over a substrate of fine (#1) silica sand for their sifting pleasure and am quite empathetic with any substrate rearrangement that occurs. The latter, conspecific aggression, has proved to be the most serious obstacle to the propagation of these exceptionally beautiful and hardy fish. Although juveniles are quite social and peaceful, I wouldn't house a mature (breeding) pair in anything less than a five foot long tank with plenty of hiding places and close to constant chaperoning. Extra conspecifics are mercilessly beaten by the pair and often outright liquidated. In the cichlid community, particularly in crowded situations where defendable rockwork is absent, Acarichthys heckelii is a model citizen with enough pluck and courage to keep from being victimized itself, while mellowing out considerably with conspecifics.

Reproduction in Captivity: The propagation of these beauties has been a dream of several year's history for me. Other than some modest lip-locking, my first group of four individuals never exhibited serious interest in generating descendents. This was most assuredly due in part to the very hard, alkaline Vermont water they were grown and housed in and the somewhat less than exemplary care they were receiving. A new batch of wild fish of various sizes, including two large (100 mm SL) individuals were received in summer of 1981 and traveled with me to the Boston area when I relocated that autumn. It became clear that the two larger fish were male and female, and in the extremely soft, acid water I was blessed with in the Boston area, the beginnings of what appeared to be serious courtship were obvious. The two fish were removed from the 80 gallon Geophagus community and placed in a breeder 50 (gallon) equipped with a large inverted flowerpot and various vertical and horizontal slate surfaces. The pair dug furiously, courted spectacularly and constantly, occasionally quarreled but, in general, acted the perfect loving couple. They were conditioned with frequent regular feedings of live red earthworms which they took greedily and soon the female was plump and obviously ripe. I waited weeks for what I thought would be the inevitable spawning, and was greeted one morning with the badly mauled corpse-to-be of the female. I nearly broke down the fishroom in disappointment! The large male (then 150 mm SL) was given away to another heckelii afficionado likewise intent on propagating them in the greater interests of the cichlid hobby.

Meanwhile, the remaining six small heckelii (mean SL ~ 60 mm) languished in a hare breeder 35 (gallon) for the better part of nine months as they slowly put on size, color, and mature finnage. Towards the beginning of summer (1982) what appeared to be courtship and abortive spawning site preparation/defense was very much in evidence, and the six now 100-110 mm SL fish were moved into a five foot long 65 gallon tank. With frequent feedings of beef heart and live red earthworms along with standard prepared foods (trout chow, shrimp pellets, and a good vegetable base pellet), the fish grew rapidly and obvious courtship and pair bonding commenced. The four largest fish became two tightly-bonded pairs staking out equal territories that split the five foot aquarium in half and kept the smaller two fish swimming frantically between the two pair at the surface (Figure 3). These two unfortunates were removed and passed on to yet another heckelii admirer.

I had not yet received copies of Cichocki's (1976) dissertation or Baran's (1981) spawning account in the DCG Journal, and Loiselle's (1980) terse description of their reproductive habits left me scratching my head. Aware of the postulated relatedness of heckelii and Guianacara geayi, the latter a known cave spawner (Haeffner 1979), I provided the two pairs with a large (12 inch diameter) overturned clay flowerpot with a hole knocked out for entrance along with a variety of vertical and horizontal slate surfaces and a deep six inch layer of fine silica sand. (Baran's [1981] successful spawning occurred in an inverted 25 cm diameter candy jar!) Fed unlimited quantities of live red earthworms and treated to massive water changes, the tandem courtships got quite stormy. Partners switched frequently, and I was often called in to referee what would certainly have resulted in fish chowder if I hadn't intervened. The egg crate divider was in and out, individuals were netted and returned: if the tank in question had not been in my office and under my almost constant watchful gaze I'm sure I'd have racked up four more pickled corpses and not the spawning I am about to report.

Thanks to Dave Palmater, the first 170 tank-reared heckelii in the USA are still happy and healthy.

Ginny and Charley Eckstein of Long Island, New York, talented aquarists and also passionate fans of this fish who have done their (exasperating) time with a large number of heckelii, confirmed my experiences with the extreme bellicosity and unpredictable moodiness of this fish. Woe betides the heckelii whose consort wakes up on the wrong side of the flowerpot! The Eckstein's experience provided one important key to the propagation of this fish. Ginny Eckstein could reproducibly induce courtship and spawning tube extrusion by simply raising the water temperature into the nineties (°F)! I began playing systematically with this parameter, raising it to 96°F and maintaining that temperature for 3-4 days, then lowering it to the high 70's for several days, and then repeating the cycle. This maneuver coupled with frequent massive water changes and almost ad libitum feeding of beef heart and red earthworms finally did the trick two weeks after adopting this strategy. Two days before I was scheduled to leave for the 1982 Milwaukee ACA convention, one of the pairs spawned inside the overturned flowerpot! I was ecstatic to say the least but equally filled with dread: should I miss the convention to tend this rare spawn? There were literally 1-2 thousand ovoid (2 mm along the major axis) ivory eggs covering literally every surface, top and sides, of the inverted flowerpot! The eggs were attached by the long axis but with no sign of a filament, however, and with considerable space between each (Figures 4 & 5). The female fanned the eggs exclusively, leaving the pot occasionally to feed or display to her mate. By now, the other pair had been removed. The next day, many of the eggs had seemingly disappeared from the pot. Had she eaten them? It seemed so, but on closer inspection there seemed to be a large number of eggs rolling around free on the glass bottom she had cleared underneath the pot. I siphoned some of these (about 200) and made the decision to leave the remainder with the female. Perhaps detachment and subsequent incubation of the free eggs on the floor of the nuptial chamber was normal behavior. By the next morning, all of the eggs had been removed from the flowerpot and, unfortunately, I did not see any of them on the glass beneath the pot. But the female remained inside the pot, and there seemed to be a chance that everything was proceeding normally. Were these fish delayed mouthbrooders?

The question that now remained was what to do with the eggs I had siphoned off? About 170 of these had been placed in a modified sponge filter incubator that successfully allows the rearing of Geophagus eggs away from the parents (Leibel 1983), and only minimal numbers had fungused. These, hatcher and all, were entrusted to David Palmater, a friend and accomplished aquarist in Cambridge, Massachusetts. The remaining 30 eggs, which had embryonated successfully in a non-aerated container, were transferred to a covered screw-topped vial and placed in a small styrofoam box along with hand lens, eye dropper, thermometer, and a small microworm culture (I'm an optimist!), and this peculiar Science Fair Kit loaded into the Winnebago that would take me the 18 hours to Milwaukee and the cichlid convention. A second friend agreed to check in on the "brooding" female and I was in touch with both her and Dave Palmater frequently by phone from the convention. It turned out that the only thing the female heckelii was "brooding" was about the apparent meal she had made of the approximately 1800 eggs I had left her, and she took out her frustration by completely de-finning her consort. The thirty Winnebago eggs survived the jolting ride through the Poconos Mountains, arrived intact in Milwaukee, and, heated by a makeshift apparatus utilizing the hotel room lamp, hatched four days post-spawn, wriggled for an additional four days, and were free-swimming and feeding on microworms the last day of our stay in Milwaukee. The newly hatched fry were apparently much less tolerant of the Poconos than the eggs themselves, and the last of the thirty fry turned belly-up as we pulled out of Pennsylvania. In all fairness to these deceased fish, my own innards were not particularly happy either.

Acarichthys heckelii female with eggs in the background Close-up of eggs of Acarichthys heckelii
Acarichthys heckelii juveniles

Figure 4 (Up-Left): Female Acarichthys heckelii guarding spawn in inverted clay flowerpot (12" diameter). Note the eggs in back wall of pot. Figure 5 (Right): Closeup of eggs. nearly 2000 ivory ovoid eggs were pasted on the vertical surfaces of the flowerpot cave. Figure 6 (Left-lower): Juvenile F1 Acarichthys heckelii.. Three months of age and 8-10 mm SL. Note flag-like iridescent splotch on anterior dorsal (see text). Photos by Wayne S. Leibel.

Thanks to Dave Palmater, the first 170 tank-reared heckelii in this country are still happy and healthy and nearly 100 mm SL eighteen months post-spawn (January 1983). The newly hatched fry were large for the size egg they came out of and could handle newly hatched brine shrimp immediately. They grew slowly at first on this diet, being outstripped by Satanoperca jurupari fry spawned at the same time and raised together with them. This situation reversed itself about two months post-spawn when weaning to dry food was finally accomplished: the fry were quite gluttonous and continued to grow very rapidly from then on. Juvenile Acarichthys heckelii are conspicuous for the previously described camouflage pattern made obvious by the barely visible iridescent striping at this age" and by the flag-like marking of the spiny dorsal (Figure 6). The first three rays of the spiny dorsal and their intermembranes are dark black, followed by a bright white-pink splash of color spread over the next 3-4 spiny rays. This marking is highly visible and may function as a semaphore that promotes schooling in these very gregarious, highly social juveniles. Cichocki (1976) reports that under water this marking is fluorescent and can be seen for many meters. He writes, "A school of young Acarichthys heckelii, their brassy-yellow flanks being invisible in the detritus suspended water, will appear as an array of blinking lights (page 371)." This fin spot, particularly the f1uorescent white-pink area, fades in adults (at about 50 mm SL) and is recalled only by the darkening of the first three spiny rays during aggressive or sexual interactions.

Guianacara geayi

Figure 7: Juvenile look-alikes: Acarichthys heckelii, Guianacara geayi above (about 40 mm SL). Photo by Wayne S. Leibel.


A second spawning attempt with this pair resulted, after two frustrating months, in the death of the female (mauled mercilessly by the mate), and a similar demise for my second mature female when spawning was again attempted. It is my fondest hope and intent that these tank-raised Acarichthys heckelii can be reared to maturity and induced to spawn. Many of the fry have been shipped to capable and interested aquarists, members of the Geophagus/Aequidens Study Group of the American Cichlid Association, and it is hoped that some one of us will succeed and that the tank-raised fish will prove less aggressive and more amenable to propagation in ensuing generations.


Special thanks to all those pivotal people mentioned variously in this article: The Ecksteins and David Palmater. Thanks also to Gary Grant for pointing out and supplying the Baran (l981) DCG article, and to Paul Loiselle for his critical reading of this manuscript.


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  • Cichocki, F.P. 1976. Cladistic history of Cichlid Fishes and Reproductive Strategies of the American Genera Acarichthys, Biotodoma, and Geophagus. Unpublished Ph.D. Dissertation, University of Michigan.
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  • Steindachner, F., 1875. Beitrage zur Kenntniss der chromiden des Amazenstromes. Sitz. Akad. Wissensch. 71: 1-68.
Guianacara geayi

Figure 8: Guianacara geayi, adult, submissive pattern. Found with heckelii throughout its Guyana distribution. Photo by Wayne S. Leibel.


Leibel, Wayne. (August 15, 1997). "Heckel's Thread-Finned Acara Acarichthys heckelii (Mueller and Troschel 1848)". Cichlid Room Companion. Retrieved on October 17, 2018, from: