A Word About Otocinclus - Updated

One or two people on this board have had problems with Otocinclus Catfishes, most notably in the form of premature demises. So, in order to prevent future Otocinclus departures, and in the process lead to happy Otocinclus owners, here are some guidelines from someone who has been very successful with them. Copy and paste this article freely into a Notepad file (or the Mac/Linux equivalent), save it, and refer to these notes as frequently as needed.

Step One : PLAN YOUR AQUARIUM IN ADVANCE. This was a MAJOR plus point in my case. I deliberately set out to stock my main aquarium with Otocinclus from the outset back in 1994, so, I checked with my LFS in advance when he was likely to stock them. I then spent time preparing the aquarium in advance for their arrival. In fact, I had a list of species prepared in advance for the aquarium, I stuck to that list for the first year of the operational life of the aquarium, and Otocinclus were on that list. Part of that preparation involved pre-soaking the bogwood pieces three months in advance, followed by their placement in the aquarium a week before the first fish went in. Just to make sure that the Otocinclus would have something to eat, I deliberately left a piece of Mopani wood in water on a window ledge for a few days so that it developed a nice crop of algae for the Otocinclus to feed on. So, when the first four Otocinclus arrived, on December 12th, 1994, they had a well-furnished aquarium with natural plants and bogwood waiting and ready to go.

Step Two : CHECK OTOCINCLUS LIKES AND DISLIKES. Which can be summarised as follows.


Well-planted aquaria with natural plants predominating;
Plenty of shady hiding places, preferably formed using pieces of bogwood;
Algae already present in the aquarium somewhere;
Regular partial water changes (NOTE : Otocinclus like 'new' water being given to them on a regular basis)
Good oxygenation levels.


Bare aquaria (they die off like flies);
No algae present (again, contributes greatly to Otocinclus deaths);
Old water (unless it happens to be very well filtered);
Stagnant water (again, they die off like flies);
Poor oxygenation levels (you guessed it, more deaths).

Step Three : WHAT CONDITIONS ARE THEY KEPT IN AT THE RETAIL OUTLET? A quote from the venerable Innes book is apposite here:

"This species causes the large wholesaler many a financial grief, for when newly received and crowded in bare containers, lacking plant life, they die off like flies. Under the conditions supplied by the retail dealer and the aquarist, they are more at home, and live satisfactorily". (Exotic Aquarium Fishes by Dr. William T. Innes, page 232).

Even back then (and Innes wrote the first edition of his book way back in the mid-1930s, when aquarists made their own undergravel filters in the tool shed, for crying out loud!) this feature of Otocinclus maintenance was known and documented. So, check your retail outlet. Do your prospective specimens have cover in their temporary home? Do they have algae to eat? Do they have relatively subdued lighting? If they're in a bare aquarium, subject to the kind of floodlighting associated with a Spinal Tap concert, and have no algae, then they're not long for this world even if you put them in intensive care and give them intravenous drips. If they have live algae to eat, and don't have to scavenge for odd bits of leftover flake food in a gunk-laden gravel bed in order to subsist, then this is a decent plus sign. Mind you, some wholesalers have at last got the message, and don't crowd Otocinclus in bare aquaria - the more enlightened ones try to give them a decent home, knowing that a little bit of money spent keeping the Otocinclus happy means that their balance sheet doesn't take a knock due to a mass die-off. It's worth checking the provenance of Otocinclus in this respect, especially if you've had past deaths despite your best efforts to acclimatise them. If the altruist and would-be Florence Nightingale gets the better of you (let's face it, we've all taken home the odd terminal case in the hope that we could save it), and you feel you have to rescue several sad-looking Otocinclus from a piscine Black Hole Of Calcutta, then be prepared for losses despite your best efforts.

Step Four : AT WHAT STAGE ARE THEY BEING ADDED? In my case, they were the first fish in the aquarium. I was actually initiating the undergravel filter cycle with them. Believe it or not, they can be used for 'cycling' an aquarium from scratch, but ONLY if suitable measures are implemented to provide them with a congenial environment (see the likes and dislikes lists above), and ONLY if one exercises patience with them, as I did. I began the aquarium with four Otocinclus, and they were the only fishes in the aquarium for six weeks. After that, in went 10 juvenile Cardinal Tetras (really small ones at that). Nothing else went in for another three months or so (partly because it took that long for me to find Corydoras pygmaeus). Be patient and build up the stocking gradually as I did, and again, Otocinclus will prove to be surprisingly tough little fishes. You CAN cycle an aquarium with them, I've done it, but you have to be patient, and you have to provide them with the right environment, so that they feel secure and are thus better able to cope with any cycling stresses that might occur. This includes making sure that they have live algae to eat, and bits of wood to chew upon. In fact, some aquarists thought I was mad because I was actually ADDING ALGAE to my aquarium ... but my Otocinlcus repaid my apparent madness by lasting a good deal longer than a week. And since then, they've prospered. If you're adding them to a mature aquarium, and it already has good planting, good bogwood provision, algae for them to feast upon, and it receives regular water changes and gravel vacs, then you should have no problems. However, an additional tip that will make life happier for the Otocinclus in a mature aquarium is this: arrange to pick up your Otocinclus on a 'water change' day, and perform the water change upon their new home BEFORE YOU PUT THEM IN. This will go a fair way toward helping them to settle in. As I said above, good oxygenation is something that Otocinclus really appreciate - they do originate from flowing waters in the wild, after all.

Oh, and as well as my oft-quoted tip of soaking bits of bogwood in jars of water exposed to sunlight to provide them with regular algal supplies, I was given a tip by Callatya on the board that is equally helpful (thanks Callatya!). If one has plants such as Amazon Swords or Cryptocoryne, and these develop sorry-looking leaves with lots of algal spots on them, the tendency of many aquarists is to prune the affected leaves and remove them. Leave the pruned leaves in with the Otocinclus, however, and they will munch on the algal spots with gusto - if Callatya's experience is anything to go by, they will utterly adore you for providing them with this treat, and become full, rounded, well-fed little fishes in no time at all. Incidentally, a well-fed Otocinclus shows a spiral pattern on the underside, where the full intestines are pressing against the outer body cavity. The sprial resembles a fingerprint in appearance, and if your Otocinclus exhibit this, then they are getting plenty of nourishment from somewhere in your aquarium, even if you can't see where they're getting it from! So, if you don't have lots of small pieces of wood or small rocks you can soak in jars, but you DO have an Amazon Sword/Aponogeton/Cryptocoryne that develops algal spots like green measles, chances are your Otocinclus will happily regard the pruned leaves as their equivalent of an asparagus treat. And, the term "Otocinclus Pet Rockā„¢" that I have taken to using (because some people soak rocks in the same way as described above) covers most of the above, whether the soaked artefact is a rock, a piece of bogwood or even some garish plastic toy of the sort that some people inflict upon their fish, and in the latter case, I can't think of a better use for the assorted day-glo monstrosities than to cover them in green fur as an Otocinclus treat!

Step Five : ARE THEY STILL DYING OFF AFTER ALL OF THE ABOVE? In other words, you've followed the above hints and tips, and you're still removing dead Otocinclus from the aquarium. You've done your tests, aquarium ammonia and nitrite readings are zero, aquarium pH is within sensible limits, and none of the other fish present are expiring, in fact, they're a sharply contrasting picture of rude health. Well, the bad news is, that occasionally, weak batches of Otocinclus do get through. More likely, however, is that they've had such a rough time before they reach you, that even your best TLC couldn't turn around the shocks and abuse that they'd suffered before you obtained them. See the notes above about what happens before and at the dealer's. If you've checked the provenance, the signs are good, and they're still dying, then you've been unlucky and bought an assortment of weaklings that were destined to expire prematurely regardless of what you did to keep them alive. This does happen, but I've only had one loss of this kind in nine years. All my other Otocinclus, including the four I cycled the aquarium with back in 1994, lasted a minimum of three years, and most a good deal longer than that. As I write this updated version of the article, my current surviving crop are at least 5 years old, and I expect they'll probably last a good two or three years with regular attention to their needs.

Step Six : ARE THEY DISAPPEARING? Otocinclus can be notorious for simply vanishing without leaving a trace of their existence. Especially in a large aquarium with lots of hiding places. I have to search high and low for mine, because they have so many nooks and crannies to call their own in my little underwater Disneyland. Finding mine can sometimes involve sending in robot submersibles (well, not quite, but you know what I mean!). If you have a team of Otocinclus living out blissfully happy lives in a huge 8ft long aquarium, with an exquisitely sculpted collection of bogwood roots festooned with Java Moss, and vast forests of Pigmy Chain Swords carpeting the substrate, then don't expect to see the Otocinclus too often! However, one unfortunate aspect of Otocinclus is that they can, and will, do stupid things now and again. Swimming into undergravel filter uplift tubes during maintenance 'down times' is a classic piece of Otocinclus stupidity. And one which guarantees the demise of whichever specimen has thus demonstrated its total lack of common sense. If I need to uncouple the powerhead on my undergravel filter for maintenance reasons, I put a cap over the uplift tube to stop such accidents, because I know there's a chance they'll happen. Especially as the uplift tube has a nice coating of tasty algae which the Otocinclus love to feast upon. And, being Otocinclus, they're apt to think that they'll get an extra share if they swim into the uplift tube after any algae growing on the inside. Then they find that they can't turn around, and the only way is down ... and at the bottom, they think "Oh, this is a nice cave I've never explored before ..." In the worst case scenario, on goes the powerhead, and it's frog in a blender time. If that makes you wince, good. TAKE PREVENTIVE MEASURES! And remember, they're like small children, in possessing an infinite capacity to satisfy curiosity in the most disastrous way possible. Mine are stupid enough at times to try their hand at rasping non-existent algae from my gravel vac. Which, when combined with frolicking Panda Corys following said gravel vac for tasty morsels that they missed first time around, makes it necessary to exhibit considerable due care and attention. At least one other poster has mentioned that Otocinclus aren't the brightest bulbs in the box. They can be fairly intelligent at times, but at others, they can exhibit the kind of blissful ignorance of impending doom that makes lemmings look paranoid.

Step Seven : SLIME COAT PROBLEMS? I must be obscenely blessed with good fortune in this regard, because, wait for it, thus far, I've NEVER had an Otocinclus try to rasp slime coat off another fish. And, I'm tempted to suggest that my above hints and tips go some way toward alleviating this. All my Otocinclus have had lots of algae to eat from day one, and I think this explains my never having seen them try and rasp another fish. Think about it - you may be an algae eater, but you're hungry, and there's no algae. What are you going to do? Starve? I'm willing to bet that if someone took the time to conduct experiments, slime coat rasping would be related to desperation for a meal. Another reason for checking the provenance of prospective acquisitions, and checking to see if they've spent time in happy surroundings. If they've had live algae to dine upon at the dealer's, and supplements of Spirulina algae wafers into the bargain, chances are they won't go looking for slime coat. One peculiarity I have noticed with mine, however, is this: they are inordinately fond of freeze dried Tubifex worms. They attack freeze dried Tubifex the way I attack a chocolate gateau. And I've been known to eat a whole one for breakfast. I have witnesses. But, this peculiarity aside, they've never shown any liking for animal foodstuffs with this one exception. They'll even brush live bloodworm aside in order to get at a particularly lush piece of algal growth on the bogwood, and ignore both Daphnia and Brine Shrimp, live or dead. I suspect they'd attack live Tubifex, if I could find a supply that wasn't riddled with vermin of the fish-killing variety - they're something I don't trust. My specimens will also snack upon bits of dead Vallisneria leaf, and rasp invisible life forms from the gravel bed, not because they have to eke out a living that way, but because said life forms are there, and the Otocinclus happen to like them. Of course, in my aquarium, the majority of their companions are a lot faster moving into the bargain, which helps, but they don't even seem to try and snatch a bit of slime coat here and there.

UPDATE : During the summer of 2004, some of my new Otocinclus exhibited some behaviour which I considered unusual. So much so that I took photographs of them in action. They ate live Bloodworm. Yes, you read that correctly, some of my Otocinclus ate live Bloodworm. Consequently, I've had to add this update as a revision of the comments above. I have photographs of them eating live Bloodworm, although to be fair, they do not exhibit this trait on a regular basis. Be advised, however, that they will eat live foods of various kinds if these are resting upon the bottom substrate. This leads me to conclude that in the wild, Otocinclus are best described as 'Aufwuchs feeders': the German word Aufwuchs is used to describe algal mats that also contain within the algal matrix a population of small animal organisms that either browse the algae, or feed upon each other. Keepers of African Rift Lake Cichlids will be familiar with this term, and also familiar with the notion that Mbuna, for example, are Aufwuchs feeders, requiring vegetable matter in the diet, but also requiring some animal matter too. The feeding habits of my Otocinclus in the aquarium now lead me to conclude, as an update to this article, that they are in fact Aufwuchs feeders, but ones that predominantly browse the algae. They will, however, add animal matter to their diet, and I suspect that this knowledge may have a bearing on breeding success with these fishes.

Now, it's time to cover some species. There are several Otocinclus to choose from, and while my old catfish book may be out of date (the volume in question is The World Of Catfishes by Midori Kobayagawa, TFH Publications, ISBN 0 86622 407 6), chances are some of the names may still be valid pending a revision of the Genus. Species listed in my book (see a couple of paragraphs below for some of the taxonomic name headaches associated with the Genus) include Otocinclus arnoldi (which I now believe to have been renamed Otocinclus mariae), O. affinis, O. flexilis, O. nattereri, O. paulinus and O. vittata. Newer ones include the highly prized Zebra Otocinclus (which I have yet to sse named, although Otocinclus zebrinus would be a perfect choice of name if someone chose to bestow it), which despite their exotic appearance, are reported to have the same care and maintenance requirements as the more familiar members of the Genus.

UPDATE: The sky high desirable Zebra Otocinclus has now been named - it is now Otocinclus cocama.

Now, after care, maintenance and the species list, breeding. Breeding is possible in the aquarium, but requires careful planning and forethought (like everything else about fishkeeping!). Otocinclus live in flowing waters in the wild, and consequently, a breeding aquarium should have a good current. Innes in his venerable book reports that Otocinclus lay their eggs singly on the underside of plant leaves, choosing plants such as Ludwigia or Hygrophyla for the purpose. After courtship dashing hither and thither, the female deposits a single egg, inverted, clasping the leaf with her pelvic fins, and the male then follows behind, fertilising it while adopting a like posture. Some specimens have been known to lay their eggs upon the aquarium glass, just to confuse matters still further! Eggs may take several days to hatch, 48 hours should be considered a minimum incubation time, and it is advisable to dose the water with a suitable anti-fungal agent to maximise survival rates. Most aquarists would probably remove the parents from the breeding aquarium after spawning is completed, but being primarily vegetarian, if they have sufficient algae to dine upon, chances are they will not eat their own eggs, although documentation in the aquarium literature on this subject seems surprisingly sparse. Once the eggs hatch, the water current should be reduced somewhat to give them a fighting chance of maintaining a hold upon their chosen perches, until they reach about 15mm in length. Needless to say, filtration should be designed not only to provide the parents with a good current (controllable), but to keep fry from becoming ingested into filter tubes etc., as I've mentioned the adults are apt to in an earlier paragraph during filter 'down times'. And, needless to say, algae and small pieces of sinking wafer food will form a large part of the diet, though it might be wise to culture some infusoria for the first week of life of the fry. I have not seen fry development stages documented in photographs, and cannot say at this stage whether they have the 'sucking disc' from the very first, or acquire it later, so it might be a good idea to give them the choice of eating infusoria in the first week or so just in case!

And after that, it's time to clear up some loose ends. Which includes the Otocinclus propensity to adopt odd resting positions, seemingly for the sheer perverse delight of it. A trait that they share, incidentally, with numerous other fishes, including Red Tailed Black Sharks and other members of the genus Labeo (now in the genus Epalzeorhynchus after a taxonomic revision). If you have an Otocinclus that happens to like sticking its head in a crevice in the bogwood, and taking a nap with its tail end sticking out at a funny angle, then rejoice in its individuality. Some people like to get comfortable in odd ways too. Wouldn't the world be a truly boring place if we all conformed to one ant-like identikit specification? So there. Otocinclus might be the kind of fishes that sometimes display woeful danger awareness, but then they are armoured with prickly armour, which leads to a certain nonchalance in the face of looming peril, such as that enjoyed by tank crews in the days before the likes of the Apache attack helicopter and its armour-piercing missiles gave them food for thought. If you're sensible about the choice of aquarium companions (i.e., don't drop them in with Piranhas, spawning Red Terror Cichlids or large Mastacembelid Eels), then they can afford to be duly nonchalant in the face of danger. You too would worry a lot less about danger if you were clad in a two-inch thick layer of chain mail atop a Kevlar blast shield. And, in the case of my specimens, the propensity for odd postures includes sitting on top of each other, piggy back style. Another aspect of Otocinclus care that crops up frequently on the board is the matter of what comes out of the back end. Now mine have never produced big long strings, but instead seem to produce miniature woody rabbit pellets. However, some people have had Otocinclus in their aquaria producing gargantuan strings of waste, sometimes several times longer than the entire body length of the fish producing them. I wouldn't worry about this, whatever kind of excrement your Otocinclus are producing, so long as they're getting a decent diet, but I have to admit, those whose fishes produce huge strings provide the board with wonderful comedy material to work with ...

Oh, yes. It should go without saying that Otocinclus are moderately gregarious fishes. They like the company of their own species, but won't necessarily pine to death without if circumstances dictate that you separate your purchases by a few weeks. And, they will socialise to a limited extent with certain other bottom dwellers of the kind that they live alongside in the wild. This means assorted Corydoras, some of the smaller Plecs such as Bristlenoses, Parotocinclus maculicauda and possibly the odd small Peckoltia too. They might even get along with the likes of Hypancistrus zebra, if you can afford to buy them. They will also happily coexist with assorted small Characins, dwarf Cichlids such as Rams or the assorted Nannacara species, and a wide range of other small, peaceful species (Danios, Barbs, the common run of Poeciliid livebearers that are listed as 'community fishes', etc). What does matter is that they have algae a-plenty to eat, hiding places to make them feel secure, and shady areas in the aquarium, especially if the overhead lighting is intense. Basically, the kind of fishes that they share their native waters with will make the best companions, but the peaceful, inoffensive Otocinclus will coexist happily with a considerable variety of companions, provided of course said companions won't regard them as lunch.

Finally, it just remains to mention that some of the taxonomic names in circulation are actually trade names, and do not have any scientific validity. Others are junior synonyms that have yet to be weeded out by a revision of the genus, as has happened with Corydoras. Mine were sold to me as Otocinclus arnoldi, a name that has been in circulation for many years, and which may either be [1] an invalid trade name, or [2] a junior synonym of Otocinclus mariae, whose illustration on matches mine very closely indeed. As a matter of fact, the webmaster at was kind enough to compare my photographs of my own specimens with the Otocinclus mariae shots in some detail, and E-Mail me with confirmation that my own specimens were in all probability Otocinclus mariae. There are several other species to choose from, and given my experience, I'd encourage others to track down Otocinclus mariae as it has always been a tough little fish in my hands. Once again, acclimatise it properly and it lasts for years. Other species might differ in this respect: if yours is confirmed as differing in identity, follow the above steps, take assiduous and careful notes, and let everyone else here know if the result is happy and long-lived Otocinclus. And if anyone out there is lucky (and wealthy!) enough to afford to purchase several specimens of the new zebra striped Otocinclus, then PLEASE take LOTS of notes, post them here on the board, and post lots of pictures too!

Enjoy your Otocinclus (as I have done for around 9 years!) and may they live long and happy lives. I recently said goodbye to the last of my original batch of four, which were introduced on December 12th, 1994, to their carefully prepared new home. It expired on March 12th, 2004 - a lifespan in excess of nine years. This is perfectly possible to achieve if you bestow tender loving care upon them!