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Biotoecus opercularis, (Steindachner 1875)

Biotoecus photos can be found here

(This article appears in the June 2001 issue of the Buntbarsche Bulletin - The Journal of the American Cichlid Association)

Biotoecus opercularis is a truly unique dwarf cichlid from Brazilian blackwater habitats. Blackwater fish have always held a special place in my heart. Such wonderful fish as the true Parrot cichlid (Hoplarchus pssiticum), Cichla sps., as well as the various dwarf Crenicichla and Apistogramma. Not to mention old favorites like Oscars, angelfish, discus, cardinal tetras and rummynose tetras. Personally, the fish at the top of my "wish list" was, for a long time, Biotoecus opercularis. It was a sort of mythical beast to me, something that could only be found in the pages of obscure academic and hobbyist literature or in the words of Old-time fish fanatics. This fish is rarely imported from Brazil or from private breeders in Europe, and when available commands a high price. Fortunately, I was able to collect and transport a breeding colony back to Boston with the help of Scott Dowd and James Carmark in January of 1999.

Bring 'em back alive

Scott, Jim, and I spent almost 3 weeks traveling the Rio Negro, sampling the diverse fish populations with our nets. This was a truly unique opportunity to find many species not imported to the States. The purpose of the trip was to participate in a field research expedition with Project Piaba and was timed to coincide with the annual Festival of Ornamental Fish in Barcelos, located 2 days (by boat) upstream of Manaus. The Festival, a truly amazing spectacle and party, is as close as Amazonia gets to celebrating Carnival.

After arriving in Manaus early one morning, we quickly loaded and boarded the , and got quickly got underway on our voyage up the Rio Negro. On the way we made several "pit-stops" including a stop to pick up a knowledgeable local guide. We stopped at his house but found it empty. We ended up waiting over an hour for him to return from catching dinner, but this time did not go to waste. After all, his home was on the banks of the Rio Jauaperi, a tributary of the Rio Negro! We paddled down a small igapo, or stream, to a spot that looked like would be home to something interesting. We jumped out of the canoe with nets and buckets in hand, ready to see what was lurking beneath the surface. Standing in the flooded forest for the first time is a feeling that I cannot describe. The feeling is very intense (especially under the effects of a Lariam-induced "purple haze." - Next time I'll just drink Gin and tonic to ward off Malaria instead!). We drew our seine nets and dipped our hand nets for 45 minutes before we decided to check on everyone back aboard the Bumerange, which at this point was looking more and more like the S.S. Minnow to me. Picking through the leaf litter, we found Acaronia nassa, Apistogramma paucisquamis, various characins and small catfish among others, but we knew that there had to be more stuff out there. Trying one last time in a promising spot by a huge fallen tree, we pulled the 6-foot seine net from about 6 feet out in 2 foot deep water all the way to the shore. As we began to sort the fish out from the vast amounts of leaf-litter, we all saw something that made us momentarily freeze, look at each other, and simultaneously say "Biotoecus." We had found them, and over 35 of them in fact during the next half hour. These were kept alive and happy during the trip and eventually we were able to export a small number of Biotoecus opercularis through a commercial ornamental fish exporter in Manaus

Since I was a college student at the time, my Biotoecus moved into the shoebox apartment I was living in. The two males and three females were housed in a 15-gallon tank filtered by a sponge filter and heated to 83 deg. F. The décor consisted of a thin layer of sand and many shards from broken flowerpots that imitated the abundant leaf litter found in blackwater streams. I took the liberty of designating one of the house's kitchen faucets as the source of feed water for my reverse-osmosis filter and set up a covered 30-gallon trash pail as a reservoir where the R.O. water treated with peat moss and heated. Needless to say my roommates were not happy, but they understood my obsession with "the ugly fish he caught in Brazil." Now that I had commandeered a faucet and sink for my needs, I figured this was a good time to tell them about the whiteworm farm stashed in a corner of my room also.

The fish did very well for the next few months, putting on size and even spawning twice for me. Unfortunately, I had, as had Scott, encountered problems raising the fry (his spawned 2 weeks earlier than mine did). Interestingly, both batches of fry (mine and his) had lived until they were about 8-10 days old. We racked our brains, comparing each other's methods, and by process of elimination came to the conclusion that the fry were not getting enough to eat.

As the semester came to a close, Scott was kind enough to baby-sit my Biotoecus, Satanoperca daemon and Hypselecara coryphaenoides that I had been keeping (in separate tanks or course!). To free up some cash and space, I moved back home to live there during my senior year at school. Shortly after moving back home, I had my old fishroom up and running. I set aside a 20-gallon long (kept "on end") "Biotoecus paradise" filled with a thin layer of "#0" gavel, Java moss, Aponogetan sps., the aforementioned flowerpot shards, short lengths of 1"PVC pipe, and even some wood I had brought back from Brazil in my suitcase. The water was again heated to 83 deg. F and filtered with a large sponge filter. The R.O. was fired up and the water used to fill 95% of the tank, with my tapwater making up the final 5%.

When I went to Scott's to reclaim my prized fish, we decided to leave al the wild-caught individuals together since they seemed to be settled-in nicely and my tanks were somewhat fresh. Luckily he had been become successful at raising Biotoecus fry and was the proud foster parent of a tank of juvenile quickly approaching sexual maturity. I returned home with one large pair and one smaller trio (1m,2f) of his F1 Biotoecus opercularis. The settled nicely into their new home. A bit later, I added some tankmates - 3 pairs of Poecilocharax weitzmani and a pair of Micropoecilia picta. The fish got along very well, there have been no deaths to this day. My water-changing regimen involved changing a quarter to third of the water every two to three weeks. Since the tank was lightly stocked and well planted, this allowed me to maintain a pH of about 4.5-5.0 without fear of a pH crash even though I refilled the tank with 95% RO water and the rest with my fairly soft tapwater. When "living on the edge" of pH safety, it is crucial that the gravel is thoroughly clean to ensure that there are not enough organics breaking down to cause a bottoming-out of pH.

The Biotoecus and others devoured the daily offerings of newly hatched SF-strain baby brine shrimp (Artemia nauplii) and shaved frozen Mysis shrimp and occasional feedings of whiteworms, glassworms, and blackworms. As could be expected, the fish rapidly put on size and weight and their coloration really stood out. It was becoming apparent that the largest male and female Biotoecus had become a pair and were getting "in the mood"

Coloration + Dimorphism

What initially appeared to be a tank full of drab gray fish, soon housed what has to be the most magnificent dwarf cichlid out there. The color of Biotoecus opercularis is very hard to describe - photos don't do it justice. Instead of the bold coloration of many cichlids, Biotoecus are unique in that they exhibit delicate pastel and iridescent colors. Mature males and females have a grayish background color with an iridescent pink/purple on the flanks. This color is more intense on females, especially the belly region, as is the yellow/green color found on her operculum. Particularly on the males, there is a string of metallic green spots along the flanks. These spots can be somewhat variable, I have seen males with either one or two rows, but a single row tends to be the norm. Both sexes exhibit a dark blotch on the operculum (hence opercularis) as well as 5 along their dorsum. There is also a mid-lateral blotch that appears depending upon the fishes' mood.

Not only does Biotoecus exhibit beautiful coloration on the body, the finnage of this species in nothing short of breathtaking, especially in sexually active males. The first 2 anterior dorsal fin spines of both sexes are usually black, again depending upon mood. Both sexes exhibit some yellow/orange in the center of the caudal along with some iridescent vertical lines and bright orange ventral fins, but this is where the similarity ends. While the female has relatively short, rounded, and uncolored (save for the metallic green in the dorsal and anal) fins, the male's fins are another story. His dorsal exhibits metallic green spots on the fin membranes and is more elongate than the female's. The caudal fin, in addition to the previously mentioned colors, shows an unbelievable combination of red and blue pastels on its lower third. The caudal also exhibits extensions of fin rays, one on the top and one on the bottom. The anal fin also exhibits the red/blue pastel coloration, but is also spangled with minute metallic yellow/green spots. The ventral fins sport long white extensions that may reach to the tip of the anal fin. Overall, it is very difficult to describe, much less photograph all the delicate colors of this fish, which is why I have taken so much space to try to do so. This is not one of those fish that can be seen from across the room - one has to take a very close look into a dim tank with indirect sunlight or diffused fluorescent lighting to get the full effect.

As with many cichlids, determining the sexes is fairly difficult until the fish start to reach sexual maturity. In the case of Biotoecus, this happens around the time the fish reach an inch and a half in length. At this point the males will become slightly more elongated than their female counterparts. When they get a bit larger, the males will start to develop extensions in the caudal and ventral fins. The females will also begin to sport the pinkish belly coloration, somewhat analogous to that of female pike cichlids (Crenichla sps.). As usual, subdominant fish of both sexes will appear very similar and hard to sex, but there is one fairly reliable way to tell them apart - the dorsal fin coloration. Both sexes exhibit a metallic green line about halfway up the dorsal fin. In males, the line generally consists of a single spot on each section of fin membrane. In females, the green is much bolder and present on both the spines and membranes, forming a continuous, unbroken line.


Over time the largest pair stayed towards the front of the tank where the flowerpot shards were most numerous. As I had hoped for, the largest female began to grow more and more rotund as she became full with eggs. At the same time, her color became more and more intense until she had transformed into what has to be the most unbelievably colored dwarf cichlid. Her once muted violet/pink sheen on the flanks and green operculum had grown very intense. Not only was color more widespread along her body, it had transformed into a metallic-pastel (if such a word exists) that looked like a combination of pink, purple, blue, and even some green thrown in. One sure-fire way to tell that your female is ready to spawn is the replacement of the orange color on the ventral fins with a metallic sky blue and a slight protrusion at the vent.

When I began to suspect that the Biotoecus might be ready to spawn, I replaced almost 30% of the tank's volume with pure R.O. water that was 3-4 degrees cooler than the tank water to mimic the rainforest's rainy season. The next morning I was pleasantly surprised to see that the fish had excavated underneath a 3"x 2" curved section of broken flowerpot. The gravel was now piled up in front of the shard, creating a very small entrance to the "love shack." Two days later, under a full moon, the female appeared ready to spawn. There was a small bulge in the urogenital area, often indicative of imminent egg laying in cichlids.

When I woke up the next morning for school, I was a bit worried because the female looked so skinny and lost most of her color. Not having had any coffee yet, my cloudy mind thought that something terrible had happened, but as she retreated to the cave, I realized they had spawned for the first time in their new home! Just visible were about 100 cream-colored eggs laid on the underside of the cave's roof. A quick check of the pH yielded a reading of 4.5 and a TDS meter reading of 38 ppm.

A Note on Courtship

Unfortunately, I have yet to witness the actual egg laying by my Biotoecus, even after seeing eggs on a dozen occasions. I have, however seen the amazing courtship display many times. The dance consists of a sort of "dive bombing" behavior on the part of the male as he attempts to show the female his choices for spawning substrates. The male will spread his fins and flare his gill covers, shaking his body in an attempt to impress the female and let her know of his desires. Eventually, the female will acknowledge his intentions with her own display. Usually within 1 to 2 days of the onset of courtship, I will come to find the female guarding a plaque of eggs.

Raising the Fry

The eggs hatch in about 3 days, at which point the female will often move the wrigglers to another excavated location with her mouth. Depending upon temperature the fry become fully free swimming at about 4 days post-hatch. At this point they are ready to eat! The Biotoecus fry are tiny and as a result need an equally diminutive food source for the next 2 days. Having learned my lesson from losing the 2 previous batches of fry, I was now ready. Thanks to my friend Luke Colliton, I had a culture of Paramecium going. I also purchased some Sera "Micron" - basically a powdered spirulina-based food. For the first day, I used a small pipette to gently "shoot" the Paramecium at the cloud of fry. Alternately, I mixed some of the dry powder with water, let it saturate for a minute, and squirted it into the fry's general area. The parents seemed to realize the presence of food and would make rapid side-to-side motions with their tails and chewing motions with their mouth, possibly alerting the fry to the presence of food. The fry could be seen making small darting movements, so I knew that they were accepting both foods. The second day, I stopped feeding the Paramecium and solely offered the powdered food. I did this frequently throughout the day, essentially every time I passed by, making sure not to overfeed at any one time.

After the fry were in the free-swimming stage for 2 days, I began to offer small amounts of newly hatched live baby brine shrimp (Artemia). I use the San Francisco strain of eggs, due to their smaller size and reportedly higher nutritional value compared to the Great Salt Lake strain. I was delighted to see a large number of the fry making efforts to consume the baby brine shrimp. Not all of the fry could swallow the shrimp, so I continued to offer the powdered food as well. After another day, all the fry seemed to be able to eat a few shrimp, so I suspended the feedings of the powder food, save a few "just in case" squirts. It was really amusing to watch the fry attack the baby brine shrimp. They would curve their bodies into the classic predatory S-bend and lurch forward, grabbing a shrimp and swallowing it. They weren't always successful, but their bellies were always full and orange in a few minutes.

The parents raised the fry until they were about 1 and a half moths old, at which time, I decided to move the 70-odd fry to a 20 "long" of their own. The grow-out tank was filled halfway with water from the parents', another quarter with fresh R.O. water, and the rest with tap water. Removing the fry was a nerve-wracking experience initially. "How the heck do I get 70 fry out of a densely planted tank full of caves?," I thought. What I ended up doing was taking a large net the width of the tank and wedging it in to form a barrier and using a smaller net to scoop the fry out. Some fry escaped, so I simply repeated it after the parents rounded them up again. The fry adapted to their new tank very well and were soon feeding on baby brine shrimp. As the fry grew, I gradually introduced shaved Mysis shrimp and eventually small pieces of blackworms to their diet. The fry reach sexual maturity somewhere at about 6-8 months of age.

Parental Care

Since I always leave the first spawn of a fish that I am not experienced with in the care of the parents, I was a bit worried about their chances for survival. I am also always out of space in my fishroom and could not afford to move the other fish a separate tank. Having 6 Poeciliocharax weitzmani, an amazing micro-predator of a tetra, in the same tank did not ease my fears. One thing I did to prevent midnight snacks was to leave the lights on 24 hours a day.

While initially the male was not present during the guarding of the eggs, he soon returned when the fry became free-swimming. As it turns out, Biotoecus are wonderful parents, easily on par with the feistier members of the genus Apistogramma. The female was very keen to chase away any fish that strayed too close to the area the pair occupied. The male was not as diligent, but did his job well. The female would actually harass the male when he "slacked off" and a tankmate came too close for comfort. Fortunately, no fish ever got close enough to the fry to pose a threat.

I no longer attempt to make water changes when the parents are guarding fry. One time after a minor 3 gallon change, the parents got spooked and led the fry to the seclusion of the rear of the tank, which happened to be where the P. weitzmani and other Biotoecus hang out. Needless to say, I never saw those fry again. Not changing water for a month or more does not seem to have any detrimental effect on the fry or their tankmates. I attribute this to the fact that the tank is very lightly stocked and well planted. Live food and stability of the aquarium environment are the keys to keeping these fish in good health.


In addition to their unique coloration, the everyday behavior of Biotoecus opercularis is fascinating. I will sometimes refer to them as "Hummingbird" cichlids, not only for their iridescent and pastel colors, but also for the way they constantly and effortlessly hover head-down with their pectorals beating like wings. They will rise and sink, move forward and back in a very precise manner just like hummingbirds. Mayland and Bork describe these fish as spending a great deal of time sitting on the bottom of the aquarium. I have rarely, if ever seen this behavior. That does not sound like a healthy Biotoecus!

Another interesting behavioral aspect of Biotoecus is the method by which the non-reproductive individuals would stalk the fry present in the tank. They would slowly make their way towards the parental pair's territory, eventually getting within striking distance by making very short darting movements. The would-be predators covered the last bit of distance by holding their bodies motionless as they crept towards the fry using their transparent pectoral fins. The stalking Biotoecus would get so close to the fry that I was sure they would snatch one from under the parents' care. Fortunately, they would rarely strike the fry if the parental Biotoecus were facing them. They would just hover motionless, centimeters away from a tasty meal. Motionless intruders were completely ignored until they made the slightest movement. It appears as though the stalking Biotoecus knew this, and as such, would only move when the parents were distracted, often by the presence of food in the tank. The stalking Biotoecus were so inept at catching the fry despite being centimeters away that I believe that this behavior may have originated as adaptation to escaping the attentions of predators with poor or motion-based vision. Kind of like the T. rex scenes in Jurrasic Park..


Overall, I found Biotoecus opercularis to be a peaceful and exceedingly beautiful dwarf cichlid. These little fish have all the personality that makes Neotropical cichlids great fish to keep. My experience with these fish has more than met my expectations. I hope that every dwarf cichlid fanatic gets to try their hand at keeping Biotoecus opercularis. Hopefully, enough captive-raised specimens will make it out into the hobby to secure its place in this country. It is a great little fish that really shines when given soft acidic water and stable conditions.


Mayland, H.J & D. Bork (1997): South American Dwarf Cichlids. Landbuch-Verlag, Hannover. 187 pages.