Category: Catfishes

Care, spawning, selection, species and genus information.

Be Careful What You Wish For

The phone call came late one night.

"Pssst. Riverfront has some Aspidoras."

"Really? How do they look? Are there lots? How much are they?" But the click of the caller hanging up was my only answer.

Hot on the trail of my only lead, I went down to Riverfront the next day. The staff seemed to know why I was there and lead me to the tank of Aspidoras maculosus. (Am I that transparent?) All my questions of the night before were answered. They looked good, there were lots, and the price was reasonable.

I observed them for quite some time to determine which were male and which were female, but apart from a slight size difference they were all identical. I had 10 bagged up with a request for some large ones and some smaller ones. So much for all my observations on fin shapes and sizes and spots or absence of spots to determine sexual differences! My wish, of course, was to be able to spawn these new fish.

A visit to any fish store will provide many different varieties of catfish but one genus not often encountered is Aspidoras. The genus Aspidoras is comprised of approximately fourteen species and is generally distributed in the Amazon region, specifically in Brazil. They very closely resemble catfish of the genus Corydoras and at first glance are often mistaken for them. The characteristic that distinguishes Aspidoras from Corydoras and Brochis is the number and shape of the cranial fontanels of which Aspidoras have two while Corydoras and Brochis have only one. This is, unfortunately, not a very convenient method of identification in that it requires dissection of the fish. However, there are two external differences that are generally reliable and easy to spot. The most apparent feature is the size of the eyes. With the exception of Aspidoras pauciradiatus, the eyes of Aspidoras are very small for the size of the fish, much smaller than those of Corydoras or Brochis. The other difference is more subtle and deals with the general body shape. Aspidoras have a rounded head shape and a longer, slimmer body than Corydoras in general, but the tiny eyes is by far the most distinguishing feature of the genus.

The fish were given a 20 liter tank with Java fern, Java moss, a floating Anubias nana, and a sponge filter. Regular tap water was used: pH 7.8, hardness approx. 250 PPM. The water was warmed somewhat from the ballast of the light fixture on the lower level and the water temperature ranged from 27C to 28C. The fish were not fussy eaters. Flake food, white worms, live tubifex worms, and shrimp pellets were all eaten with relish and over a few months the larger females became much fuller in girth than the smaller males. But the fish did not spawn.

I knew of two aquarists who had also purchased some of these fish and were having spawning success so with some further sleuthing I learned that in one case, the eggs were laid on the uplift tube of the AquaClear filter and in the other case, the female actually jumped into the chamber of the AquaClear filter to deposit her eggs. Of course, Watson! I needed more current! To this end I added an AquaClear mini to one end of the tank. No filter medium was used in the chamber as the purpose was to increase the water current and the sponge filter was also still running to take care of biological filtration.

As I was feeding the fish late one night in February, three or four weeks after adding more current, I saw a female swimming with eggs in her pelvic fins. After three or four jubilant dances around the room I watched a bit longer but couldn’t see where the eggs were being placed. I wanted to wait until morning before moving the eggs to give them a chance to harden and minimize the chance of damaging them.

First thing in the morning, I looked for the eggs in the Java moss and on the back of the Java fern but there were none there, nor were there any on the glass. I eventually found the eggs on the underside of an Anubias leaf all clustered together in one clump. There were about 35 eggs and they all appeared to be fertile. I moved the cluster of eggs into a margarine container of tank water that had been lightly tinged with methylene blue. In my hunt for the eggs, I also found two fry living under the sponge filter. Hmm Watson, what could this mean? Obviously, there had been a previous spawn(s) that I had not detected.

The eggs developed very quickly and hatched in only three days. As soon as the fry hatched, they were moved to a small show tank with about two inches of fresh water. The fry absorbed their yolk sacs for another three to four days and then took brine shrimp nauplii as a first food. Unlike Corydoras fry, the Aspidoras fry undulate their tails constantly. Each day the bottom of the tank was siphoned with air line tubing to remove any uneaten food and detritus. Keeping the bottom of the tank clean is of paramount importance in preventing the growth of fungus. Fungus will attack the fry, usually starting at the end of the tail and traveling up the body, eventually killing the fish. The first signs are a clamped caudal fin and translucence of the tail. AquariSol administered in the regular dosage will help prevent fungus but scrupulous cleanliness is the best defense.

The fry grew very quickly, much faster than any cory fry I’ve raised, and it was necessary to move them into a 20 liter tank with a sponge filter and some rocks to hide under after about two weeks. The fry ate to the point where their bellies were very distended and looked so uncomfortable balanced on their swollen tummies, leaning on one pectoral fin that I often thought that throwing in a couple of Tums would do them a world of good. But they ate like that meal after meal without any ill effects and grew like weeds in the process.

Once I had discovered where the Aspidoras laid their eggs, I began to search regularly, and also began to find regularly, clusters of eggs almost always on the undersides of the Anubias leaves. I was never able to observe the T-formation of the spawning act and, in fact, the only spawning activity I ever witnessed was when I first saw the female swimming with eggs in her fins. I was able to determine that spawning always takes place late at night and eggs are always grouped in large clusters, usually one but sometimes two or three. I found this very interesting as it suggests a greater effort to hide the eggs from predators rather than scattering them all over the glass as with Corydoras aeneus. The parents never ate the eggs and there were many times that I found clusters of eggs on the verge of hatching. The fry, however, must be much tastier for they disappear if not removed from the tank although a few do find refuge under the filter.

I only experienced one problem with this fish and for a while it was quite a mystery to me. On occasion, I found a dead adult fish without a mark on it to indicate the cause of death. As the fish were eating and spawning and regular water maintenance was being done, I was at a loss to explain the deaths. The fish were full-sized when purchased so it was impossible to determine their age and I wondered if they were dying of old age (always a convenient excuse) but others also keeping this species were not having similar problems. Not very much literature is available on this genus of fish but I poured over what little there is. In two separate sources I found mention that Aspidoras like oxygen-rich water. I’m reasonably certain that the temperature of their tank water is too high to permit oxygen solubility at the necessary level to sustain as many fish as I was trying to maintain in one tank. In short, I think I suffocated some of them.

Many books recommend Corydoras paleatus or Corydoras aeneus for their relative ease of spawning as two species to try when first attempting to spawn a catfish but I have found this Aspidoras easier in both inducing spawning and raising of fry. In fact, I was so caught up in the joy of finding egg clusters, hatching and raising the fry that it took me some time to realize that I was overrun with kittens. At present, ten tanks in my fishroom have Aspidoras in residence and I’ve willed myself to stop looking for eggs. But like the Sorcerer’s Apprentice, I seem to have started something I can’t stop. The last time I did a water change and siphoned the detritus off the bottom of the tank, I found a newly hatched group of 40 fry in my water change bucket. These are currently living with a group of C. paleatus fry the same age. There are also eight fry about a half inch long growing up in the tank with the parents. The first fry, only 8 months old, have begun laying eggs, too. So, be careful what you wish for…


Colored Atlas of Miniature Catfish, Warren E. Burgess, T.F.H. Publications Inc., 1992.

Aquarium Atlas, Volume 2, Hans A. Baensch and Dr. Rudiger Riehl, Hans A. Baensch GmbH, Melle, Germany, 1993.

Aquarium Atlas, Volume 3, Hans

The Plecostomus

Once upon a time in a land not so far away there lived a plecostomus. His simple but fulfilling home was underneath a swordplant, at least that’s where he preferred to sleep, when he wanted to sleep, which was most of the time. He was a very good looking plecostomus; without being vain; with a tall, fine boned dorsal fin that gave observers the impression of maturity but not arrogance, and wonderful, unusual markings that were tasteful but not overdone. It was many times remarked upon by visitors that he was very well grown for his age and that his mouth was particularly apt at rasping algae.

He was a very happy fish, sleeping cozily under his plant most of the day except when his little friends the corys came nosing about, trying to get under him just in case the choicest morsels of shrimp pellets were there. The metal halide was directly above, and he would enjoy its warmth as he lay snoozing, imagining the delightful food he would eat later that night. But the best time was at night, when his hired help would serve a late supper including zucchini for dessert. When the lights went out, he would loosen up his raspers with an easy warm-up exercise and settle in for some serious dining. In the morning he would glide back to his favorite resting spot and drift off, just another easy day.

Then one day his world was turned upside down. In the middle of his afternoon siesta there was a noise like thunder and sunlight came flooding down. He twitched his fins in agitation and his tail swished violently across the gravel. The glass top slid open with a squeal and everyone swam for cover. In came the hose, and out went some water. A splash and hands came down, his beloved swordplant was carefully rearranged. It was all just too much and he flared his fins up and out. Should he stay or should he go? Wait where did that bucket come from? Why is it so close? Nooooo not the bucket! Out came the bucket, and down went the lid, but not before there was a great deal of splashing, soaking, and sputtering.

Up the stairs, down the hall, out the door, and into the warm summer day. In the car, shut the door. Up the road – lots of traffic. Watch the pothole, around the men doing construction, stop for the red light (hmmm those brakes need looking at). Big bump, gravel drumming against the bottom of the car, more potholes, stop the car. Various noise, some clanking. Move the bucket, bright light. People talking, water pouring, gravel falling. Finally the lid comes off. He is not a happy plecostomus. Lift the bucket, into the water, not quite home but pretty close. And there’s even a swordplant and some driftwood. He thrashed around trying to get comfortable; the driftwood was too small for a proper fin rest and the plant wasn’t big enough for him to get under. After he had worked through all his frustrations and decided to settle down, he could hear the admiring murmurs. Admiring and appreciating. “Fine specimen.” “Beautiful scale patterns.” “Rare variations on the species.” “Not a flaw on him.”

For three not so easy days, he displayed more frequently than he did typically and moved around somewhat, but not too much for the quarters were confining. The whole experience was repeated, but it was more complicated this time. Out came the plant, scattering gravel, out came the driftwood, no more hiding places left. In came the hose, out went the water. The bucket again! At the end of the harrowing car ride was his home, with his own swordplant that he slid under very gratefully. All he wanted was an extra large portion of zucchini and that’s just what he got. On the wall, his blue ribbon hung.

Eenie Meenie Minie Moe

Catch a tiger by the toe, If he hollers let him go, Eenie Meenie Minie Moe. Now to choose a female. Eenie Meenie Minie Moe… While this method is somewhat less than scientific, it is the most commonly used procedure in acquiring a group of catfish in which some are male and some are female. While most fishes available in stores are in the juvenile or “teenage” stage, catfish are almost always adult specimens. This is to our advantage because once mature or nearly mature, catfish show varying degrees of sexual dimorphism and the sexes can be distinguished quite easily in many cases. So let’s see what’s out there.

The most commonly kept catfishes are of the genus Corydoras and there are a great many varieties available. Since these are also the most commonly spawned catfishes, let’s start here. In much of the available literature, the authors may go as far as to say that females are larger than males or males are slimmer than females and my all-time favorite, females are fuller and stouter at spawning time. Corys are not available in stores in spawning condition so this bit of information is not particularly useful. If you have already purchased six or eight fish and conditioned them, the difference between sexes will become more noticeable but with the high cost of some corys, it would be more desirable to purchase the specific spawning group.

Some corys have such great sexual dimorphism as to make one suspect the male and female are of different species. Some that come to mind are C. barbatus, C. undulatus, and C. elegans; although there are others. In these three species, the female has the same general markings as the male but they are less distinct and less intense. In C. barbatus, the male has additional cheek bristles and a light-colored stripe running down his nose to make him look even more like another species.

Many corys show differences in fin shapes between the sexes. For example, in C. agassizii and C. wotroi, the pelvic fins of the male are longer and pointed while in the female, the pelvic fins are more paddle shaped, presumably for carrying the eggs at spawning time. See Figure 1.

Corydoras macropterus, C. paleatus, and C. steindachneri (among others) have a much longer dorsal fin on the male of the species. On some species of Corydoras, the difference in the dorsal fin of the male is not as pronounced but is evident on close inspection. Two examples are C. adolfoi and C. pygmaeus. In his book, A Fishkeeper’s Guide to South American Catfishes, Dr. David Sands reports C. trilineatus as being “Difficult to sex, but adult females are generally more robust than males.”

In fact, these are one of the easiest corys to sex in that the males have noticeable black speckles on the pelvic fins while those of the female are clear. Other corys with black speckles on the pelvic fins of the males are C. nanus and a species that I bought as the “San Juan cory”. Male C. nanus are also distinguishable from the females by a darker blotch on the dorsal fin.

Sometimes, despite out best efforts, it is difficult to pick out a definitive difference in a group of corys. When viewed from above, females are wider even when not in spawning condition. If you are on good terms with your local fish store, ask to see a group in an ice cream bucket to get a view from above. A top view will show males and females as in Figure 2. Although the difference in girth may not be as dramatic as shown, there will certainly be a size difference unless the fish are too young.

There are many other available species of Corydoras that I have not dealt with here but these common principles can be applied to any cory. Most corys have some external differences between the sexes and careful observation will detect them. Generally, males may have any of the following: more pigment on the body or fins; longer and more pointy fins; speckles on the pelvic fins, and a slimmer, more stream-lined body shape.

Some of the other commonly kept types of catfishes also show sexual dimorphism, often to a much greater extent than do Corydoras species. For instance, male catfish of the genus Callichthys and Hoplosternum have a much thicker and longer first ray on the pectoral fins. At spawning time, these thickened spines turn orange with some species. As the fish come to the surface to feed, it is also possible to see the difference in the breast plates of males and females. On males, the breast plates are larger and more overlapping while those of the female do not completely touch at the center and are much smaller. These differences are shown in Figure 3. These drawings are of Hoplosternum littorale and other species may have somewhat smaller plates for both males and females. The Farlowella, Sturisoma, and whiptail-type species show sexual dimorphism mainly, but not exclusively, in the head region of the two sexes. On male Farlowella catfish, easily visible bristles appear on the sides of the nose at spawning time. As well, the nose of the male is flatter and wider than that of the female. Figure 4 shows the nose detail of a Farlowella species. When not in spawning condition, the overall body shape can be used to determine sex. Males are generally longer, slimmer fish while females are shorter and thicker through the middle. (Picture, if you will, Clint Beaton and myself standing side by side and you will understand what I mean). When the female is in spawning condition and full of eggs, she is very thick through the middle leaving no doubt that spawning is imminent.

Sturisoma and Rineloricaria species males develop bristles in varying degrees on the cheeks, head, and pectoral fins. On some species these bristles are difficult to see unless you are looking specifically for them. Rineloricaria morrowi males are covered from head to tail in bristly fur making them look very shaggy indeed. Sturisoma males develop the bristles mainly on the cheeks and the males can be identified in this way when only 75 mm in total length (not including tail filaments). Rineloricaria and related species develop bristles on the cheeks, top of the head, and top of the pectoral fins. These bristles are not only present at spawning time, for I have three males together without a female and they all show head, cheek, and fin bristles. Rineloricaria females have the same overall body shape as males and are not particularly plump at spawning time so these are not good indicators of sexual difference. Sturisoma females get very plump at spawning time and can be easily differentiated from males which stay much slimmer.

Catfishes are not as difficult to sex as we’ve been given to believe. Knowing what to look for makes the task quite straightforward and simple. Take the test; see if the information I’ve presented enables you to determine the sex of some catfish that you keep. I’m betting that it will!



The World of Catfishes by Midori Kobayagawa, TFH Publications Inc., Neptune N.J. 1991

Aquarium Atlas 2, by Hans A. Baensch, Mergus-Verlag, Germany, 1993

A Fishkeeper’s Guide to South American Catfishes by David Sands, Tetra Press 1988

Colored Atlas of Miniature Catfish by Dr. Warren E. Burgess, TFH Publications Inc. Neptune N.J. 1992