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FAQs on Otocinclus Behavior

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Related Catfish FAQs: Otocinclus 1, Otocinclus 2, & FAQs on: Otocinclus Identification, Otocinclus Compatibility, Otocinclus Selection, Otocinclus Systems, Otocinclus Feeding, Otocinclus Health, Otocinclus Reproduction, & Suckermouth Catfishes of South and Central America, Loricariid Identification, Loricariid Behavior, Loricariid Compatibility, Loricariid Selection, Loricariid Systems, Loricariid Feeding, Loricariid Reproduction, Loricariid Disease, Catfish: Identification, Behavior, Compatibility, Selection, Systems, Feeding, Disease, Reproduction Algae Eaters

Otocinclus staying at water surface      1/21/15
I purchased 5 Otocinclus 4 days ago and have them in a 10 gallon quarantine tank. If all goes well, I plan to add them to my 55 gallon show tank after a month or so to help control the brown diatom algae (I think I must have silicates in my tap water causing the brown algae growth because it has always been a problem in this tank for over a year).
<I wouldn't get my hopes up on this! Five Otocinclus won't have a massive impact on a 55 gallon tank, and while they eat some diatoms, they prefer green algae. Snails, particularly Nerites, are the best at eating diatoms, but more often than not, if you get the rest of the tank balanced, and plant growth strong, a simple wipe of the front glass is enough to keep the diatoms minimised.>
Today one of the Otos started hanging out at the very top of the tank on the glass right at the water surface. Sometimes I think its nose might even be just out of the water. Is this something I should be worried about?
Could this be a sign of low oxygen in the tank, and if so what should I do?
<Yes, can easily be this, but also other problems. Otocinclus tend to be starved on import, and their survival rate isn't good.
Getting them through the first month is a good sign. I often recommend getting something like twice as many as you need, because that really is the level of mortality we're looking at. Some retailers do get them in healthy condition prior to purchase, in which case you may do a lot better than this. Also some species, like Parotocinclus jumbo, seem to be a lot tougher. But the average Otocinclus from the average pet store aren't a safe investment.>
I set up the quarantine tank about 5 days before purchasing the new Otocinclus. I filled it halfway with water from my larger tank and then the rest of the way with Prime treated tap water, and moved a filter cartridge from my larger established tank to the quarantine tank's hang on back filter. The larger tank is fully cycled and has been stocked with the same fish without any problems for over a year. The quarantine tank is decorated with fake plants and has small rocks on the bottom. I also moved some of the rocks from my larger tank that were covered with brown diatom algae so the Otos would have something to graze on when I added them.
The new Otocinclus seem to really love the brown algae.
<Quite so. They're aufwuchs grazers and consume both diatoms and green algae, but also various micro-invertebrates. A good green turf would be the idea.>
I have also been feeding them small pieces of Hikari algae wafers and today I added a small piece of blanched zucchini.
<All good.>
I remove any uneaten food daily. I checked the water conditions today and they were Ammonia 0, Nitrite 0, Nitrate <20, GH 75, KH 300+, pH 7.5. Any ideas why this one Oto is hanging out at the water surface?
<Hard to say. Stress, sickness, sensitivity to something... by all means observe and optimise water conditions. But no treatment as such beyond hoping for the best.>
Thanks so much,
<Most welcome. Neale.>

Question about my Oto cat   7/31/11
Hey there,
A while ago I had a 10 gallon tank with 4 Guppies and an Oto Cat.
<A bit small for Guppies.>
The Oto did just fine, was always eating, and very lazy.
<Shouldn't be "lazy" at all. This SCHOOLING species should be buzzing about in a group of five or more specimens, pretty much all the time, flitting from leaf to leaf.>
Now I have a new tank with 4 GloFish and an Oto Cat.
<Again with "an" Otocinclus. They're schooling fish that don't do well singly.>
This is my second Oto for this tank the first died after two days.
<Unfortunately a very common experience. Most aquarists kill their specimens quite quickly, and retailers aren't any better at all.>
When I took it back the pet store they said it was because it was under fed.
<Likely correct. Otocinclus are notoriously difficult to feed. In the wild they consume green algae (not diatoms, and not hair, bush or thread algae either) alongside what is called aufwuchs, tiny invertebrates that live among green algae. In captivity they can be maintained in mature tanks with a combination of green algae, finely minced seafood, and standard algae wafers, but they don't compete well for food and shouldn't be kept alongside greedy fish that feed in the same way, e.g., loaches or catfish.>
So I got another one and put blanched zucchini in the tank, as many sites said they'll like.
<Some specimens will eat softened vegetables, but it's not 100% reliable.>
Problem is he hasn't touched it. I don't want to starve another one.. I have also put in an algae wafer and he hasn't touch that either. He keeps sucking the sides and swimming all over from side to side of the tank like he's looking for something to eat. Any suggestions??
<Will likely not settle down without four or more friends of his own kind.
In a group this species is happier, and therefore more ready to feed.>
Should I just wait to see if he makes it or not?
<If you want, but I'd put money on a swift death.>
Also right now I'm leaving the light on 12 hours to try and grow algae.
<Green algae needs strong lighting to grow. If you have plants that grow so quickly you have to remove a handful of foliage every week or two, you probably have the right amount of light. If your plants basically sit there and throw out the odd leaf every few weeks, then you probably don't have strong lighting and the dominant algae types will be diatoms (the brown scum on the glass) and red algae (hair, brush and thread algae, which aren't red, despite the common name for this group).>
I'm stumped I don't know what else to do.
<I'm surprised you're stumped, because the aquarium literature on Otocinclus spp. is actually quite good. Most any tropical fish book will tell you that these catfish need to be kept in groups, need cool water (22-25 C/72-77 F), and are difficult to feed.>
I attached 2 picture to see if your think he's okay or not. He's slightly blurry because he wouldn't sit still. He's very active. Thank you!!
<Glad to help.>
P.S The pet store got new fish in Thursday and Friday when I brought my dead one back and got the new one, he was the last one left. I'm not sure if they just sold that quick or if there was a reason to why they didn't get more.
<Many pet shops buy Otocinclus because they know [a] they die quickly and [b] people will keep buying new ones to replace any losses. Somehow, there's a rumour that Otocinclus are good algae eaters for small tanks.
That's total and 100% rubbish, but sadly you'll hear it said in some pet shops and written on web sites by people who perhaps don't know any better.
There are some excellent catfish sites, like PlanetCatfish, that will provide very useful information.>
It just seemed weird to me.
<Not weird; typical.>
I checked and there was no dead fish in the tank so I assume they were all in good health. I was thinking of getting another one so he has company, but no other pet stores around here sell them. If this one doesn't work out I'm going to stay away from them for a while as much as I don't want to... I really like these little guys.
<I agree with you that this genus is best avoided by casual aquarists. They can work in largish (20+ gallons?) systems with bright lighting and lots of plants, where there's enough growth of green algae to supplement algae wafers and other such foods. In smaller tanks and less brightly lit tanks they become totally dependent upon the aquarist to feed them, and that is very difficult to do. Not impossible, but difficult, and you do need to ensure two or more small meals per day. Kept singly the poor thing may well be so nervous it'll never feed adequately well. For small tanks Nerite snails are infinitely better algae-eaters, not least of all because they consume diatoms. Hope this helps. Cheers, Neale.>

Re: Question about my Oto cat   7/31/11
Thanks for your help Neale.
<You're welcome.>
So basically I need to get more, which is impossible because the pet store is out,
<Otocinclus spp. aren't rare, and shopping around or online should yield results. Alternatively, ask your retailer to order some in.>
or take him back/wait for him to die and get something else..
<Pretty much.>
do you have any other suggestions other then snails? I always start out with one snail and end up with like 10.
<Nerites don't breed in freshwater; they lay eggs, but the larvae need to drift to the sea and develop in the plankton. This is why I specifically recommend Nerites. One or two per 5 gallons is about right.>
At pet smart they have albino Cory catfish in the tank with the Glofish but it says they get to 3" and I think that's to big for a ten gallon though it says 10+ gallons on the tag.
<Albino Catfish are typically Corydoras paleatus, and while they could be kept in a 10 gallon tank, they wouldn't be my recommendation. Yes, exceptional specimens can exceed 7.5 cm/3 inches, though 5 cm/2 inches is much more typical. Do read the following for more on stocking:
Would it be okay if I moved my Oto out of the tank to feed or would it stress him out more.
<Yes, that would be stressful. Guppies shouldn't compete against him for food, but Corydoras surely would, at least in a tank this small. Nerites and Cherry Shrimps would be the most logical bottom feeders.>
I'm really wanting to keep him around. Thanks again.
<Cheers, Neale.>

Otocinclus.. sys., comp., beh.    3/22/11
My name is Jessica, thank you for your help in advance. I have been keeping Goldfish ever since I got my first ten gallon aquarium at the age of nine.
For the past two years, I have had a 29 gallon freshwater planted tank, which is also home to one brand new, week old, two inch Fantail Goldfish and two Otocinclus.
<Mmm... not really compatible fishes... like very different water quality mixes>
The tank parameters are as follows, pH 6.4,
<Low for Goldfish>
Nitrites 0, Nitrates 20ppm or less,
<I would not let the NO3 concentration get any higher than this maximum>
Ammonia 0, and temp 70-72F. I do a weekly 25-50% water change and vacuum the gravel at the same time while tending the plants. It is well water so I don't need to add a dechlorinator. I bought the two Otocinclus about two months ago and they have done an amazing job cleaning up the algae in the tank. At the time the aquarium was home to an eight inch, five year old Bubble Eye Goldfish who has since passed on. His one eye bubble got so big that he kept catching it in his mouth. It became irritated and in the 24 hours that I was not there it managed to become infected and swollen. I placed him in the hospital tank and gave him antibiotics but sadly his eye popped and he died two days later. Since then I have been substituting the Otocinclus's algae diet with some zucchini and Spirulina wafers and have left the back and sides of the tank alone for them to clean. When I first got them they both had Ich and one of them had almost its entire caudal fin missing. Unfortunately, I read that this was rather commonplace during the shipping process.
<This is so>
Anyway, its fin has regrown and they both seem to be doing fine. What concerns me is that their dorsal fins always seems to be held tight against their bodies, they have been this way since I got them, is this just normal behavior for them?
<Mmm, yes. A general statement re freshwater fishes is that their fins are "down" for most of the time, vs. marine fishes, whose fins are "up" most of the time>
They seem happy otherwise zooming around the tank and they really love their zucchini, although the new goldfish is fighting them for it. Also, I was thinking of raising the pH just a little bit, up to 6.8, and to this end was thinking of boiling some shells, cracking them, and placing them in a glass bottle in the tank.
<Worth trying>
That way the fish could not get cut on them and they would be easy to take out if the pH got too high. Do you think this is a good idea or would you recommend to just leave the pH alone as is?
<I might instead add a bit of sodium bicarbonate (baking soda) to a given batch of make-up water (in storage and tested ahead of use) to get a proportion of how much you'd be adding to raise the pH on a regular basis... but the shells are again a good/safe source. Bob Fenner>

Cory/Oto behavior change  5/19/10
Hi crew:
Thanks as always for all that you do.
<Kind of you to say so.>
My question concerns a change in behavior by some of the fish in my tank. Tank specs as follows:
Tank: 10 gallon standard
Filtration: Aqueon 10 HOB with pre-filter sponge (x2) each rated for 100gph
Temp: 76F
pH: 7.2
NH3: 0ppm
NO2: 0ppm
NO3: ~10ppm
Above tested via API Freshwater Test Kit
Total Alkalinity: 180ppm (tested via strip... not really sure what this number represents)
<Middling hardness, fine for most purposes.>
Total Hardness: 120ppm (tested via strip... not really sure what this number represents)
<Similar. Do read:
20% water change weekly
Flora (moderately planted):
Cryptocoryne wendtii x2
Cryptocoryne parva x2
Anubias barteri v. 'Nana'
Microsorium pteropus
Ceratopteris thalictroides - rooted
Eleocharis acicularis
Remnants of Java moss - mostly removed as it was constantly infested with thread algae
<Yes, never had much luck with this plant myself. Always seems to do well where I don't want it, but badly everywhere else.>
Hitchhiker duckweed
<The world's best ammonia remover! A blessing of sorts, but a nuisance I know.>
Corydoras pygmaeus x6
Boraras maculatus x15
Otocinclus affinis x3
Assassin Snails (started with 2 adults, now numerous juveniles)
Hitchhiker pond snails
<Sounds grand! It's a real joy to read about a sensibly stocked 10 gallon tank.>
Tank was set up and planted in October, stocked in January.
I've observed a change in behavior in my Corys and Otos over the last few weeks. In the past, the Otos would spend time on the front and side glass of the tank during all hours of the day/night. Lately, they stay in the small space between the HOB filter and the back glass of the tank.
<Possibly more food there?>
They will venture down to the substrate at night to eat algae wafers (Hikari brand), but ignore the blanched zucchini and carrots I place in the tank which they used to eat with gusto.
The Corys, while always skittish, used to venture around the tank in a shoal, especially when I fed the Rasboras. After not seeing any of them for weeks, and assuming they had perished somehow, I found them hiding in a tiny crevice, all on top of each other, between the driftwood and the substrate, when I shined a flashlight into the tank to try to find them. They also now seem to venture out only at night for the sinking wafers (Hikari brand) I place in the tank at lights out. I know that Corys are nocturnal in the wild, but this is a recent development, hence my concern.
I'm not sure what caused the change in behavior as my feeding and maintenance regimens have remained the same. Water quality has also remained constant.
<That would be my first though, as well as variation in pH and problems with oxygenation. Since both Otocinclus and Corydoras prefer cooler rather than warmer conditions, check the temperature. 25 C/77 F is the absolute tops for both species.>
My first thought is an aggression issue with the Rasboras, but I have never observed any aggression.
I had also thought that I might need to add Corys to the tank to see if increasing the size of the shoal would bring them out into the open more often, but I believe my tank to be fully stocked as is.
<Oh, I'd chance it. With all the plants I think you'd be fine. I'd keep at least 5 Otocinclus, and maybe double the number of Corydoras pygmaeus. All these fish are so small that their impact on water quality would be fairly trivial.>
Do you have any thoughts on what would cause this change in behavior and if there is something else I should be doing?
<My guess would be something is scaring them -- too much overhead light, noise/vibration outside the aquarium, banging doors or some such. Direct sunlight can also be a thing. I have a 15 gallon tank that gets direct sunlight for a couple of months of the year, and the way the fish behave becomes noticeably different during those times. The Corydoras paleatus in particular cluster in one particular shady spot under the Anubias mother plant.>
Thanks in advance.
<Cheers, Neale.>

Otos coloration: Sick or normal? I got four new Otos on Monday. Stupidly, I put them in my tank without first a quarantine (this won't happen again, trust me). I may just be paranoid but I am wondering about their coloration. It looks splotchy to me and I was wondering if this is normal or if it might be something I need to take care of.  < Hard to say what the problem is. It is normal for fish to have a fright pattern when being introduced into a new tank. As they begin to feel more comfortable than they start looking more normal. Many times these algae eaters are starved at the wholesalers and at the local store. I would place an algae wafer in the tank at night to make sure they are getting something to eat. If the splotchy pattern continues with all the fish or gets worse then I might start thinking there is a problem. -Chuck>  I am attaching two pictures. If you need any other details, please ask. Thank you for your time.  David

Once playful Otos are now lethargic   7/28/06 Hello there, <Hi from... HI!> For the past 5 months, I have owned a 46 gallon, unplanted tank, containing 10 rummy nosed tetras, 10 black phantom tetras, 4 peppered Corys, and 3 Otos. <Better with live plants...> The Otos were originally quite playful, moved around the tank, stayed within view, interacted with other fish and ate any algae that appeared.  However, for about the past month, the Otos have been in hiding. <Something in the way of water quality changed> Now I hardly ever see them, and algae is building up on the glass and plastic plants.   They don't appear to be sick, and none have died.  All the other fish appear to be normal.  My water temperature has increased to about 82 degrees due to the warmer summer weather, but besides that, I can't think of anything that I've changed. I do 20% water changes once every week or two, and nitrate level is 12.5 mg/L or lower (my test kit measures only measures 1, 0, 12.5, and 25 mg/L).  I don't add any "Oto specific" food to the tank.  Might I simply have more algae than they can handle, allowing them to become more "lazy"?  Do you have any thoughts on the matter? <Yes... I definitely would add some live plant material here... Will address many possible ills, shortfalls that could be at play here... Dissolved oxygen, food, shelter...> Thanks in advance for your help. Bonnie <Welcome. Please read here: http://wetwebmedia.com/FWSubWebIndex/otocinclusart.htm and the linked files above. Bob Fenner>

Oto loses colour Hi, We have a sick Oto which has suddenly lost its pigmentation and is looking a sickly grey. It is swims weakly, sometimes floating at the surface and drifting in the current. Otherwise its body, fins, etc. look in good condition. Can you suggest any remedy or is this something to do with the tank conditions? We have a 180-litre (40 gallon) community tank with 9 guppies, 3 minnows, a Pleco and 5 Otos altogether. It has some live and plastic plants, a couple of logs and a small rock pile (slate), i.e. there is a relatively large surface area available for the Otos to graze on. It has been set up for about 3 months, but, about 3 weeks ago, we had problems with water quality, fungus and white spot. These were successfully treated with 10% water changes every day and ESHA 2000 and EXIT. Treatment finished 7 days ago. Current conditions pH = 7.8, KH = 6°, GH = 12°. Ammonia, nitrite and nitrate levels all low. We have isolated the sick Oto. Grateful for your advice. Regards, Quentin <Hello Quentin. Let me start by making a general statement about Otocinclus: they are extremely difficult to maintain, and the vast majority die soon after import. The problem is that they feed on really only a single thing -- aufwuchs, a combination of green (and exclusively green!) algae together with the tiny invertebrates that live within that green algae 'biofilm'. Unless you have an established aquarium of large size with very strong lighting (2+ watts per gallon) so that green algae can flourish, it is exceedingly unlikely your Otocinclus will be getting enough to eat. How many months it is before they die is variable, but starve they will unless ample substitutes are provided. Algae wafers can work, but Otocinclus find it difficult to compete with other fish, and the fact you have other algae-eaters, specifically guppies and Plecs, makes this point critical. For this reason, I simply don't recommend them as community fish. Furthermore, while water chemistry itself isn't all that important, temperature and water quality are very important. Most people keep their tanks far too warm for Otocinclus, which come from cool, fast-flowing streams and want something in the 20-25 degrees C range rather than the usual 24-28 degrees C most people maintain standard community tropicals at. In other words, a near-subtropical, fast-water tank with things like White Cloud Mountain Minnows and Danios is much closer to what they want than a standard Amazon community aquarium. You also mention ammonia and nitrite levels as being "low" -- but be under no illusions here, Otocinclus MUST have zero levels of both. If you can detect either in your tank, it is simply not suitable for Otocinclus. In all likelihood the sickly specimen will be dead within a few days, so treatment here is irrelevant. Optimizing water quality, lowering water temperature, providing ample green algae and suitable invertebrates would all be things you could do to help the isolated fish, but that's about it. For the rest, you need to ensure your aquarium satisfies the demands outlined above. Hope this helps, Neale.>

Re: Oto loses colour 7/6/08 Neale, Many thanks for your helpful advice. The Oto has now died, sadly. However, we will develop the tank environment to make it better suited to Otocinclus. They are an entertaining fish to watch. <Yes they are. In the right tank, they can be great fun. In the wrong tank though... My most recent run-in with this species was a disaster, some of the Otocinclus deciding to graze on the mucous of some large benthic gobies. They have a reputation for attacking big, slow moving fish such as Discus and Angelfish. On the other hand, aquarists like Takashi Amano make much use of Otocinclus in planted aquaria, usually alongside Caridina shrimps as a superb combination for green algae control in brightly lit aquaria.> Thanks again. Your website is a mine of information and a great support to the budding enthusiasts in our family. Regards, Quentin <We're happy to help, and thanks for the kind words. Cheers, Neale.>

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