The one thing that decides whether yours lives
Every other record on this site opens with a water figure. This one opens with a supply chain, because the most common cause of death here happens before you get the fish home.
Both our sources say the same thing in different words. Seriously Fish notes that it is a small fish that needs to feed almost constantly, so it is easily starved during transportation. Aquarium Co-Op is blunter, describing animals that may have gone three to six weeks without adequate food before they reach you, and adding that once one is starved it is often hard to get it to eat again.
That is an unusual thing for two independent care sources to agree on, and it reframes the whole record. The water figures below are easy: 70 to 79 °F, pH 6.0 to 7.5, a range most community tanks already sit inside. What is not easy is putting a fish that eats constantly into a tank that has something for it to eat.
So the practical order is backwards from the usual one. The tank runs first, it grows algae, and the fish goes in afterwards. A brand new tank with a brand new oto in it is the arrangement that kills them, and it is also the arrangement almost every shop sells.
Why this record was written now
- The gap
- Not one fish on this site ate algae. The corydoras record says so explicitly, and every question about algae had to be answered by pointing at a shrimp or a snail.
- What it changes
- The fish silo now has a grazer in it, and the substrate layer has a fish alongside the invertebrates rather than only invertebrates.
- What it does not
- Two fields stay blank. Not one of our four sources states a lifespan or a growth rate for this animal, and no figure has been borrowed to fill them.
Three species, one shop label
Otocinclus is a genus, and the tank at the shop usually says oto. Aquarium Co-Op names three sold under it: Otocinclus vittatus as the common oto, O. macrospilus as the dwarf oto and O. cocama as the zebra oto. Seriously Fish profiles them separately, and two of those profiles do not agree.
| Field | O. macrospilus | O. cocama |
|---|---|---|
| Sold as | Dwarf oto | Zebra oto |
| Max standard length | 1.4 in (35 mm) | 1.6 to 1.8 in (40 to 45 mm) |
| Temperature | 70 to 79 °F | 70 to 77 °F |
| pH | 5.5 to 7.5 | 6.0 to 7.5 |
| Hardness | 18 to 215 ppm | 36 to 179 ppm |
| Base dimensions | 45 by 30 cm | 45 by 30 cm |
| Described | Eigenmann & Allen, 1942 | Reis, 2004 |
Which of those figures the record prints
The dwarf is the small one, and it is not the one called dwarf
Read the size row. The fish sold as the dwarf oto has a maximum standard length of 35 mm; the zebra reaches 40 to 45. The trade name describes the price bracket the fish sits in rather than the animal, which is the same pattern our corydoras record found with the albino.
The practical difference between them is smaller than the label suggests and it is real: the zebra tops out two degrees cooler and will not take water as acidic. If you have the striped one, the ceiling on this record is 77 rather than 79.
| Field | Seriously Fish | Aquarium Co-Op | Flip Aquatics | Splashy Fish |
|---|---|---|---|---|
| Minimum tank | 45 by 30 cm base | not stated | 10 gal | 20 gal for six |
| Group size | shoaling, no number | 6 or more | 4 to 6 | at least 5 to 6 |
| Temperature | 70 to 79 °F | 70 to 79 °F | 70 to 79 °F | 72 to 79 °F |
| pH | 5.5 to 7.5 | 6.0 to 7.5 | 6.0 to 7.5 | 6.5 to 7.5 |
| Hardness | 18 to 215 ppm | not stated | not stated | 6 to 15 dGH |
| Adult size | 1.4 to 1.8 in | up to 2 in | 1 to 2 in | 1.5 to 2 in |
| Lifespan | not stated | not stated | not stated | not stated |
| Safe with shrimp | not stated | not stated | no threat to shrimp or snails | not stated |
Peaceful is the first word both care guides use
Two of our care guides open on temperament, and they open on the same word. Aquarium Co-Op titles its guide a peaceful schooling algae eater. Flip Aquatics calls the otocinclus catfish peaceful and states it poses no threat to shrimp, snails or nano fish.
The record files it as peaceful, shoaling, easily out-competed, and the third word is the one that matters. Peaceful here is not a virtue, it is a vulnerability: a fish that will not compete for food, in a tank where something else is eating first, is a fish that starves quietly while looking healthy for a fortnight. Nothing in this record is about aggression. Everything in it is about whether the animal gets to eat.
Ten gallons, or twenty, and the problem is ours
This record prints a 10 gallon minimum and asks for six otocinclus catfish or more. Splashy Fish states 20 gallons or larger for groups of six, and once you read that sentence the two figures on our own record stop agreeing with each other.
Both halves are defensible on their own. Ten gallons meets the 45 by 30 centimeter base that Seriously Fish states for both species it profiles, and Flip Aquatics states 10 gallons outright. Six or more is what Aquarium Co-Op asks for, and the welfare argument for it is in the station above.
- What we are not going to do is average them into twelve or fifteen gallons. No source states that, and a figure nobody published is worse than a disagreement somebody did.
- What the honest reading is: ten gallons is the floor for the tank, and six is the floor for the group, and only one source has looked at both numbers at once. That source says the pair does not fit.
- What decides it in practice is not water volume, it is grazing surface. A 10 gallon tank with mature glass, hardscape and plants feeds more of these fish than a bare twenty does, and every source here agrees an otocinclus catfish is eating a film rather than swimming in a volume.
- Where to check the arithmetic: the stocking calculator uses 10 as the floor and prints the group figure beside it, so the tension is visible there rather than hidden in an average.
Plants are the plate, not the decoration
Three of our four care guides put this fish in a heavily planted tank, and one of them lists the species by name: Anubias, Java fern, Java moss, Cryptocoryne, Vallisneria and Amazon sword. Flip Aquatics describes the otocinclus catfish as working the plants, the hardscape and the glass, which is three grazing surfaces rather than one.
That is the same point the tank size argument arrives at from the other direction. Leaves are surface area, and surface area is food for an animal that eats a film. The aquarium plants silo holds what we have verified about the plants themselves, and none of it is recorded as an otocinclus requirement, because no source states one as a requirement.
Flip Aquatics also states the thing people ask before buying: an otocinclus catfish poses no threat to shrimp, snails or nano fish. Our cherry shrimp and nerite snail records hold no refusal against it, and this is one of the few combinations on the site where a source says so in as many words rather than leaving us to read a silence.
What the record above prints
The figures at the top of this page are the tighter of the two profiles wherever they differ, because a genus record that printed the widest span of everything would describe no fish in particular. Temperature is the exception: 70 to 79 is what both our genus level source and the dwarf profile state, and the zebra ceiling is printed here rather than hidden in an average.
The name on your receipt is worth checking against this table before you set the heater.
The full record
| Field | Recorded | Where it comes from |
|---|---|---|
| Minimum tank | 10 gal | Flip Aquatics states 10 gallons outright, and Seriously Fish gives a base of at least 45 by 30 cm for both species it profiles, which a 10 gallon meets. Splashy Fish disagrees: 20 gallons or larger for groups of six. Since this record also asks for six or more, that is a tension between our own two figures and it is printed rather than averaged. |
| Temperature | 70 to 79 °F | Aquarium Co-Op and Seriously Fish give the same range for the dwarf oto, 21 to 26 °C, which is the only figure on this record both sources state identically. The zebra oto profile stops at 25 °C, or 77 °F, and the table below prints it. Flip Aquatics states 70 to 79 as well, three sources on the same range. Splashy Fish starts two degrees warmer, at 72. |
| pH | 6.0 to 7.5 | Aquarium Co-Op and the zebra oto profile agree on 6.0 to 7.5. The dwarf oto profile goes lower, to 5.5, so this is the tighter of the two rather than the widest we could print. Flip Aquatics gives the same 6.0 to 7.5; Splashy Fish is tighter at 6.5 to 7.5. |
| Hardness | 36 to 179 ppm | The overlap of two Seriously Fish profiles: the dwarf oto at 1 to 12 °H, about 18 to 215 ppm, and the zebra oto at 36 to 179 ppm directly. Aquarium Co-Op says soft to hard water and gives no figure. |
| Adult size | 1.4 to 2 in (35 to 50 mm) | The span across three profiles: Seriously Fish gives 35 mm standard length for the dwarf oto and 40 to 45 mm for the zebra oto, and Aquarium Co-Op gives 1.5 to 2 inches for the genus. The fish sold as dwarf is the smallest of them. Flip Aquatics gives 1 to 2 inches and Splashy Fish 1.5 to 2, both rounder than the standard lengths the species profiles measure. |
| Diet | Algae, biofilm and diatoms | Both sources. Aquarium Co-Op is specific about which algae: softer green algae and brown diatoms, and not black beard or green spot algae. Both name the same substitutes for when a tank runs out, algae wafers and blanched vegetables. |
| Water column | Substrate, and every flat surface above it | Ours, from the behavior Aquarium Co-Op describes, grazing or resting on the ground and on flat surfaces. We do not file it as a bottom dweller competing with our corydoras and kuhli loach records, because the same source names both of those as tank mates for it. |
| Lifespan | Not recorded yet | Not stated by any of our four sources: neither Seriously Fish species profile, nor Aquarium Co-Op, nor Flip Aquatics, nor Splashy Fish. Left blank on purpose. This is a fish that often dies in its first month from starvation rather than from age, so a figure taken from tanks would be measuring the supply chain. |
| Growth rate | Not recorded yet | Not stated by either source, on the genus guide or on the two species profiles. |
The same nine fields for every animal on this site are in the A to Z index.
Where our sources disagree
The disagreement on this record is the group size, and it is not a small one: one source says six or more and the other says a couple. Both are arguing about the same thing from different ends, which is why the record prints both.
Seriously Fish
Very shy and retiring, to the point that it will be out-competed for food by more vigorous species. Gregarious by nature and should ideally be maintained in a group of 6 specimens or more.
Aquarium Co-Op
A couple of plump and healthy otos are preferred over a larger group, because too many of them may end up consuming all the algae.
What we record: we print six or more and attach the condition the second source is really making. Neither statement is about the fish being happier alone: one is about the animal being shy and out-fed, the other is about the tank running out of the food this animal is bought for.
Both are true at once, and together they say something neither says on its own, which is that the group size is a function of how much algae your tank actually grows.
Six, or a couple
The disagreement above is the sharpest on this site, and it is worth reading twice because Seriously Fish and Aquarium Co-Op are right about different things.
The welfare argument
Seriously Fish calls the species very shy and retiring, to the point that it will be out-competed for food by more vigorous species, and asks for a group of six or more. That is an argument about the animal: a timid shoaling fish alone in a community tank feeds last and least.
It is also consistent with everything else on this site. Our corydoras record asks for six or more of one species, our ember tetra record for eight to ten, and in both cases the source is describing what the otocinclus needs rather than what a keeper finds convenient.
The food supply argument
Aquarium Co-Op prefers a couple of plump and healthy otos to a larger group, for a reason that has nothing to do with the fish: too many of them may end up consuming all the algae. That is an argument about the tank, and it is the sentence the entire first station of this record turns on.
Neither Seriously Fish nor Aquarium Co-Op is telling you an oto is happier alone. Between them they are saying that the right number is however many your tank can actually feed, and that if six would strip it in two weeks then six is not a group, it is a countdown.
Six or more, with the condition attached. The welfare figure is the one a source states as a number, and the other is a constraint on it rather than a competing figure. A tank that cannot feed six is a tank that has to be fed by hand, which both sources describe how to do.
How much algae a given tank grows, which is the number that would settle this. Nothing we hold converts tank size, light or planting into a quantity of food, so the record cannot turn this into arithmetic and does not pretend to.
What an oto eats, and what it will not touch
This is the record where the diet field carries the most weight, because the otocinclus catfish is bought for its diet rather than in spite of it. Aquarium Co-Op is specific in a way most sources are not: they specialize in softer algae, meaning soft green algae and brown diatoms, and they avoid black beard algae and green spot algae.
Which means an otocinclus catfish is not a solution to your algae
It is a solution to two kinds of it. The brown diatom film that coats a new tank is exactly what this fish is for. The black tufts on your driftwood and the hard green dots on the glass are not, and buying six otos to remove them is buying six animals that will starve beside the algae you wanted gone.
Our water and health topic has nothing written about either of those algae types yet, and this is the clearest example on the site of why the queue there matters.
What to feed when the tank runs out
Every source we hold names the same category of thing, and the two later ones add to the list. Algae wafers and spirulina, blanched vegetables, and Aquarium Co-Op gets specific with canned green beans, softened zucchini slices and a gel food. Seriously Fish adds that an oto will accept small live and frozen foods such as bloodworm or daphnia, and to take care not to feed those too often.
Driftwood and catappa leaves appear on the equipment list rather than the food list, and they belong on both: they are surfaces that grow the biofilm this fish grazes between feedings.
Filed with the grazers, not the catfish floor
Our records file each animal under the part of the water it uses, and this is the first fish on the site filed under the substrate rather than under a swimming layer. Aquarium Co-Op describes it grazing or resting on the ground and on flat surfaces, which is the same behavior our cherry shrimp and nerite snail records are filed under.
Why not the bottom
Because our one stocking rule is one group per layer, and filing this fish as a bottom dweller would put it in competition with our corydoras and kuhli loach records. The same source that describes its habits names corydoras and kuhli loaches as tank mates for it, so a rule of ours that contradicted a statement of theirs would be the rule getting it wrong.
The substrate layer is the one place our stocking tool already allows sharing, for exactly this reason: our sources describe grazers as company for each other rather than as alternatives.
The competition nobody states
There is one thing worth flagging as ours rather than as a source’s. An otocinclus catfish and a nerite snail eat the same thing off the same surfaces, and Aquarium Co-Op warns that too many otos strip a tank of algae. Nothing we hold says whether that matters when the two are kept together.
So the record does not print a warning about it. It prints the observation, and the note that no source we name has taken a position either way.
What goes wrong, in order of frequency
It arrives already starving
This is first because it is the one that kills them, and it happens before you own the fish. An otocinclus catfish is wild caught, moved through several holding tanks with nothing to graze, and sold looking thin rather than looking ill. Nothing about the tank you put it in fixes a fish that ran out of food two weeks ago, which is why every other failure on this list is downstream of this one.
A tank with nothing growing in it
Soft green algae, biofilm and brown diatoms are the diet on every source we hold, and all three are things a tank grows over weeks rather than things you add on the day. A brand new setup with clean glass is a plate with nothing on it. Our sources do not phrase a mature tank as a rule and everything they state points at one.
Bought to fix an algae problem
Aquarium Co-Op names which algae this fish eats and, by omission, which it does not: not black beard, not green spot. So an otocinclus catfish bought to clear an established outbreak is being asked to eat the one thing it cannot, in a tank whose soft algae is already gone. It is a grazer of a tank in balance, not a treatment for one that is not.
Something else eating first
The record files this fish as peaceful, shoaling and easily out-competed, and the third word is the failure. A cherry shrimp colony, a nerite snail and an otocinclus all work the same surfaces for the same film. None of them attacks the others and the smallest eater still loses, quietly, over a month.
The wrong two degrees
The zebra oto stops at 77 °F where the dwarf goes to 79, and the shop label is the least reliable thing in this record. A tank held at 79 for a fish sold under the wrong trade name is outside the only range its own species profile gives.
Six fish in a tank that feeds four
Our sources put the group between four and six and one of them says six needs twenty gallons rather than ten. The number that matters is not the one the water supports, it is the one the surfaces support, and that is the disagreement printed further up this page rather than a figure we are going to invent.
Questions about otocinclus catfish care
Why do otocinclus die in the first few weeks?
Starvation, on the evidence of both our sources. Seriously Fish states an otocinclus needs to feed almost constantly and is easily starved during transportation; Aquarium Co-Op describes animals arriving after three to six weeks without adequate food and adds that once starved they are hard to get eating again. The fix is a tank that is already growing algae before the fish arrives.
How many otocinclus should I keep?
Our sources disagree and both reasons matter. Seriously Fish asks for six or more because the fish is shy and gets out-competed for food. Aquarium Co-Op prefers a couple because too many will strip the tank of the algae they live on. We print six or more with that condition attached: the right number is what your tank can feed.
What size tank does an otocinclus need?
Ten gallons on this record, and Flip Aquatics states it outright. Seriously Fish gives a base of at least 45 by 30 cm for both species it profiles, which a standard ten gallon meets on length and misses on depth by about five centimeters. Aquarium Co-Op states no tank size for this fish at all.
Will otocinclus clear my algae?
Two kinds of it. Aquarium Co-Op states they specialize in softer algae, soft green algae and brown diatoms, and that they avoid black beard algae and green spot algae. If what you have is black tufts or hard green dots, this fish is not the answer and will starve next to them.
What temperature do otocinclus need?
70 to 79 °F, and three of our four sources state it identically, which is the only field on this record that manages that. If yours is a zebra oto, the Seriously Fish profile for that species stops at 25 °C, or 77 °F, which is the tighter ceiling and the one to set the heater by.
Can otocinclus live with shrimp and snails?
Aquarium Co-Op names snails and dwarf shrimp among its tank mates, along with tetras, rasboras, corydoras and kuhli loaches. On our own records the water agrees too: it shares 70 to 79 °F with the cherry shrimp and 72 to 79 with the nerite snail.
What should I avoid keeping with them?
Aggressive species and large fish that can eat them, per Aquarium Co-Op, and that is the whole of what our sources state. Seriously Fish adds the subtler version of the same point: this fish is retiring enough to be out-competed for food by more vigorous species, so a tank of fast eaters is a problem even when nothing attacks it.
How big do otocinclus get?
1.4 to 2 inches across the three profiles we hold. Seriously Fish gives 35 mm standard length for the dwarf oto and 40 to 45 mm for the zebra; Aquarium Co-Op gives 1.5 to 2 inches for the genus. The fish sold as dwarf is the smallest of them, which is the reverse of what the name suggests.
How long do otocinclus live?
Not one of our four sources states a figure, so the field is blank. On this particular record that blank is more honest than most: a fish that commonly dies of starvation in its first month has a life expectancy dominated by husbandry rather than by biology, and no number we could borrow would tell you anything.
What is the otocinclus lifespan?
Not one of our four sources states a figure. Not the two Seriously Fish species profiles, not Aquarium Co-Op, not Flip Aquatics, not Splashy Fish. The field on this record is blank and it is going to stay blank until somebody publishes one.
That silence is worth reading rather than filling. This is a fish that very often dies in its first month from starvation rather than from age, so a number taken from tanks would be measuring the shops and the shipping as much as the animal.
Are otocinclus catfish safe with shrimp and snails?
Flip Aquatics states it directly: they pose no threat to other inhabitants like shrimp, snails or nano fish. That is the only source of the four that addresses it, and it is one of the few places on this site where a compatibility answer comes from a sentence rather than from the absence of a warning.
The reverse question matters more here. An otocinclus catfish competes with a cherry shrimp colony and a nerite snail for the same biofilm and soft green algae, and a tank that feeds all three is a bigger tank than one that feeds any one of them.
How many otocinclus in a 10 gallon tank?
Our sources do not agree, and this is the widest disagreement on the record. Aquarium Co-Op asks for six or more, Flip Aquatics says a group of four to six in a 10 gallon tank, and Splashy Fish says a group of six needs 20 gallons or larger.
So the range across four care guides for a 10 gallon tank is four to six fish, with one source saying six does not belong there at all. What none of them disagrees about is that the number is limited by how much the tank can feed rather than by how much water it holds.
Do otocinclus need a planted tank?
No source states it as a requirement, and three of the four recommend it. Splashy Fish names Anubias, Java fern, Java moss, Cryptocoryne, Vallisneria and Amazon sword; Flip Aquatics describes a heavily planted setup and lists plants alongside hardscape and glass as the surfaces the fish works.
Read it as grazing area rather than as decoration. Leaves are the plate this fish eats off, which is why a planted 10 gallon can carry a group a bare one cannot.
What to feed otocinclus, and how often?
Algae first, and it has to already be there. Aquarium Co-Op is specific about which: softer green algae and brown diatoms, not black beard and not green spot. Then supplement, because a tank runs out. Flip Aquatics names sinking kelp wafers and plant based foods when algae are sparse; Splashy Fish names algae wafers, spirulina based food and blanched zucchini, cucumber and spinach.
How often is the part people get wrong. This is a grazer, not a fish that eats at feeding time, so the question is whether there is film on the glass at three in the afternoon rather than whether you fed it this morning. A tank with nothing growing on its surfaces is a tank with nothing to offer on day one.
Do otocinclus eat shrimp?
No. Flip Aquatics states that they pose no threat to other inhabitants like shrimp, snails or nano fish, and no source we hold says otherwise. The mouth is built to rasp film off a hard surface and does nothing else.
The real question runs the other way, and this record does not dodge it: an otocinclus catfish and a cherry shrimp colony eat the same soft green algae and biofilm off the same surfaces, and so does a nerite snail. Nobody eats anybody. They all run out of food together.
Are otocinclus hardy?
Once settled, on the evidence of the numbers: the temperature band is nine degrees wide, three sources give the same one, and the pH band spans a point and a half. Those are not the figures of a delicate fish.
Getting there is the problem, and it is why this record leads with it. The animal arrives having gone weeks with nothing to graze, it will not compete for food once it is in your tank, and it is hard to restart once starved. So it is a hardy fish with a fragile first month, and almost everything written about otocinclus being difficult is describing that month rather than the species.
What are the otocinclus types sold in shops?
Two, mostly, and the names are unreliable. The fish sold as the dwarf oto is Otocinclus macrospilus, with a maximum standard length of 35 mm. The one sold as the zebra oto is Otocinclus cocama, at 40 to 45 mm, so the one called dwarf is the smaller of the two only because the trade name describes a price bracket rather than an animal.
The difference that matters is in the table above. The zebra tops out at 77 °F against 79, and will not take water as acidic. Aquarium Co-Op writes about the genus rather than about either species, which is why this record prints the overlap and names which figure came from where.
Do I need a mature tank before buying them?
Our sources do not phrase it as a rule, and everything they do state points at it. The fish eats biofilm and diatoms constantly, arrives having gone weeks without food, and is hard to restart once starved. A tank with nothing growing on its surfaces has nothing to offer it on day one.
The other algae eater on this site is now written. Our bristlenose pleco record covers four kinds of algae to this record's two, asks for twenty gallons rather than ten, and is kept as one fish rather than six. Both records carry a source saying that the algae in your tank will not feed the animal.
This site now holds a second algae eater, and it eats the algae this one will not. Our siamese algae eater record carries four sources and all four name black beard algae, which is the algae this record names as the one its fish does not touch. The two share a layer on our tank mates grid and share a warning as well, since both records carry a source saying algae alone will not feed the fish. What they do not share is the tank: this record asks for a 10 gallon and that one asks for 40, and that one asks for filtration rated 430 to 755 liters per hour, where this record describes a fish that is easily out-competed in a busy tank. The bands overlap from 75 to 79 °F, which is the whole of the other record’s range.
What this fish needs that a stocked tank may not have
Three things, and the first one is not equipment at all.
- A tank that has been running long enough to grow algaethe fish arrives starved
- Algae wafers and blanched vegetablesgreen beans, zucchini, spinach
- Driftwood and catappa leavessurfaces that grow biofilm
Every item our records ask for is gathered on the tank setup topic.
Nothing here is a paid link. It is the shortfall between what this record asks for and what a boxed kit contains.
How this record was compiled
- By
- Verified
- Sources
Seriously Fish, Otocinclus macrospilus, Seriously Fish, Otocinclus cocama, Aquarium Co-Op, Flip Aquatics and Splashy Fish
- Conflicts
Printed above: six or more against a couple, and the reason each source gives
- Blanks
Lifespan and growth rate stay empty until a source we trust states them
- Not recorded
A lifespan, a growth rate, and a minimum tank from the second source