How to Care for Otocinclus: A Complete Fact Sheet, Breeding, Behavior, and Care Guide

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While Otocinclus are hearty, useful algae eaters for a home tank, it takes a little extra effort to move them from one aquarium to another. I have used that one fact often to evaluate fish when I visit a pet store.

Here is my simple guide:

  • If stocks in other tanks are low, and the Otocinclus are healthy, I figure the pet store is doing a better job than most when it comes to managing new fish. 
  • If there are few or no healthy Otocinclus, then I know any fish I buy will wind up being possible rescues as opposed to serious purchases for my community tanks. 
  • If stocks in all tanks are high, then I know they probably got a new shipment of fish within the last 24 hours and it will take a few days to see how the numbers change.
otocinclus care guide

Otocinclus is a fast moving, sucker mouth fish that feeds on algae. Females are slightly larger and wider bodied than males. Both carry a dark horizontal stripe in a field of green to brown. Many aquarium keepers prefer Otocinclus because they do not get very big.

Healthy Otocinclus will dart quickly around the tank. You may also spot them hanging off rocks, or the sides of the tank to feed on any algae growth building up on these surfaces. 

Quick Intro to Otocinclus

FamilyLoricariidae
Scientific NameOtocinclus vittatus
Other NamesGolden Oto, Midget Sucker Fish, Dwarf Sucker Fish, Oto Cat, Otocinclus Catfish, Dwarf Suckermouth, Dwarf Oto
Care LevelIntermediate. Most people rate these fish as easy to care for. I rate them as intermediate because extra care must be taken during the acclimation process and in the first few weeks in the home tank. If the fish survive one month, then the maintenance level drops considerably.

Natural Habitat, Identification, and Where To Buy

Otocinclus originate in the freshwater spanning Columbia to Argentina. Their natural habitat usually has a good bit of drift wood, sand, and algae. The water itself is slow moving but clean.

When you visit a pet store, you are likely to find a number of other freshwater fish that are sold as algae eaters and may even be mistakenly marked as Otocinclus.

You can actually buy Otocinclus on Amazon:

This includes Siamese Algae Eaters, Chinese Algae Eaters, and Siamese Flying Foxes.

Even though these fish look similar to Otocinclus, their growth characteristics and temperament may be different. This article is dedicated to Otocinclus.

otocinclus in planted aquarium sucking on glass

Optimal Water Conditions For Otocinclus

Temperature70 – 78 degrees Fahrenheit
Water Flow RateSlow moving, high in oxygen content.
HardnessSoft
Aquarium Salt RecommendationsBest to avoid aquarium salt
Tannin RecommendationsOk, but increase gradually
Other Water Chemistry NeedsMust keep nitrates below 20 ppm. Otocinclus are also very sensitive to pesticides and other chemicals. Be careful when feeding them natural foods that may be contaminated with pesticides.

Tank Setup

Minimum Tank Size10 Gallons
Optimal Tank Size20 Gallons
Optimal Tank ShapeLong and shallow
Recommended Filter TypeCanister with nitrite and nitrate filter pad
Extra Air Flow and and How to Provide ItUse airstones with low to medium flow near the bottom of the tank. Otocinclus do not like a lot of water current, so having patches with less flow is helpful to them. I do not recommend air curtains because the current will be too much.

Otocinclus are very sensitive to nitrates. It is important to test the water quality weekly.

Use nitrate removing pads in the filter and plenty of live plants to keep nitrates low. You may need to do partial water changes in emergencies to keep the nitrates down even if ammonia and nitrites are at zero levels. If this happens more than twice in a month, you may need to move some fish out of the tank.

Even though all fish have a certain amount of sensitivity to water chemistry changes, Otocinclus tend to have more problems than others. This is not a fish that you can simply dump into a tank after 20 minutes of waiting for temperature adjustment.

Here are the basic steps I recommend for optimal survival rates

Step 1

Ask for extra water from the pet store. Make sure you have at least 1 gallon.

Step 2

You will also need a 2 – 3 gallon tank, and a 5 gallon tank during the quarantine period.

Step 3

Next, make sure you test the water from the store. Make sure it is free of ammonia, nitrites, and nitrates. If the water has any of these substances in it, use zeolites and nitrite/nitrate absorbing pads until the problem is resolved. You can also add an airstone to improve water circulation.

Step 4

Once these problems are resolved, you can start acclimating the fish to the community tank water.

Remove one gallon of water from the community tank and place it in a water jug.

Start a siphon with aquarium tubing. Allow one drop of water per second to go from the jug to the Otocinclus temporary quarantine tank. Watch carefully for signs of distress. Offer the fish some food and see if they eat it.

After the jug is empty, wait a few hours, and then add more water from the community tank via the siphon. Continue adding just one drop per minute until the tank is full.

Step 5

Keep the fish in the 2 – 3 gallon tank until they show good appetite, are alert, and begin to play and explore. Feed them frozen or live food during this time along with sinking algae wafers. Watch the water chemistry carefully.

Step 6

After about 1 week, you can move them up to a 5 gallon tank. Use all the water from the 2 – 3 gallon tank. Once again, you will need to slowly drip water a gallon at a time from the community tank.

Step 7

Keep the Otos in the quarantine tank for an additional 3 weeks. Watch carefully for signs of disease. If you see fungus or other infections, you will need to give the fish antibiotics and resolve that before moving the fish into the community tank.

Step 8

During these 3 weeks, change out 1 gallon every 3 days via the drip method to keep the water chemistries as close as possible. On moving day, the pH and hardness should be the same.

Step 9

Most people will tell you to discard the water from the quarantine tank because it may have disease bearing organisms in it. Unfortunately, all fish carry low level opportunistic infections.

Adding new fish to an established tank is always risky. Established fish can still have immune system collapses caused by the stress of living with new tank mates. I have done acclimation both ways and have had tank wide infections both ways. I’ve also had perfectly successful transfers both ways.

You can try using UV sterilization systems on the water before releasing it back into the community tank. Just remember this will also kill off useful bacteria. I do not recommend treating the water with antibiotics as you might need to use several of them that might create toxic compounds when mixed.

oto fish in tank on rock with red shrimp

Creating the Landscape

Otocinclus move rapidly, but still need plenty of places to hide. The best landscape for them will include plenty of plants and smooth rocks that will build up algae. 

Best PlantsA combination of fast and slow growing plants. Use the fast ones to keep the nitrates down. The fish will prefer slower growing plants that they can eat algae from. Mosses can also be used to create places for them to explore and hide.
Best LightingBright
Best DecorationsSand will work better than gravel because it does not have sharp edges that can damage Otocinclus’ mouth. They also enjoy habitats with drift wood, caves, and rounded stones.
Decorations to AvoidAnything with sharp surfaces or edges. Otocinclus are always looking for algae to eat. If there is a sharp surface under the algae, it can easily cut into their suckers and allow infections to occur.

Physiological Considerations

Maximum Size2 Inches
Rate of GrowthWill reach maximum size in about a year
Life Span5-7 Years
TemperamentUsually peaceful but may be drawn to suck on the slime coats of other fish. They are easily preyed on by larger or more aggressive fish.
Preferred Tank RegionBottom
Scale ThicknessOtocinclus do not have scales. They do have armor plates that protect them from other fish to a point. The plates do not stop pesticides, heavy metals, salt, antibiotics, or other chemicals reaching deep into the fish’s body. As a result, great care must be taken when exposing Otocinclus to chemicals of any kind.
Swimbladder ConsiderationsSince Otocinclus originate in slow moving water, they may have a hard time maintaining balance if the water circulates too fast. A shallow tank will also be more relaxing to them.
Gill ConsiderationsFrom time to time, you may see Otocinclus rise to the surface. They are capable of taking in some air through their gills and using it. If you see Otocinclus rising to the surface more than normal, you may need to add more plants to increase oxygen levels.
Fin Shape ConsiderationsCompact and strong

Society

Among themselves, Otocinclus can display territorial aggression. Nevertheless, they are shoaling fish and do best when there are at least six of their species in the tank.

They are relatively peaceful when it comes to interacting with fish from other species. Otocinclus work well with Corydoras and other non-aggressive fish.

Try not to put Otos in tanks with Angel Fish and other deep bodied or slow moving fish. Larger fish may act aggressively towards Otocinclus. Otos will be drawn to larger fish and try to latch onto them in order to feed on their slime coat. Needless to say, this can be a serious problem for both species.

There is no particular male to female ratio for Otocinclus. Males will chase females that are about to release eggs – however, they will not hurt the females.

As with other species of fish, Otocinclus will splay their fins and become more brightly colored when warning other fish. They will also chase other fish and harass them if there is a territorial challenge.

The best way to deal with an aggressive Otocinclus is to put the whole school in a bigger tank. You can also try adding more hiding places so that weaker fish can stay out of the bully’s way.

It may also be of some use to add more Otocinclus to the tank. These fish can become more aggressive if they feel insecure.

As a last resort, you can try isolating an aggressive Otocinclus. These fish are very social creatures, so it might not do well all once isolated. If you only had six of this species in the tank, be sure to replace it with another fish.

Once the bully is gone, another may take up that role, especially if the rest of the school feels less secure.

Gender, Breeding, and Reproductive Considerations

Since Otocinclus females produce less than 10 eggs per cycle, you might think they are a good species to try raising from fry.

Depending on where you buy the fish, it is very likely they are wild caught. This in turn means there is a good chance breeding pairs will produce healthy and viable offspring.

Because Otocinclus are very sensitive to water chemistry changes, I recommend keeping breeding pairs in a tank by themselves. Once the males start chasing a female around, partition off that female with one male.

From there, you will need to watch carefully to see when the female lays her eggs. Be sure there is plenty of moss and other materials that the eggs can get lost in. There is considerable controversy over whether or not Otocinclus will eat their own eggs.

To be on the safe side, move the male and female back into the other partition of the tank once the eggs are fertilized. This will give the eggs and resulting fry a safe place to live until they are big enough to move into another tank.

Once the fry are free swimming, you can feed them infusorans and algae. There are also commercial fry foods available that will not foul the water as much as hard boiled egg yolk or other foods.

Many aquarium keepers recommend feeding brine shrimp to young fry. I have personally seen even tiny, newly hatched brine shrimp cause considerable damage to free swimming fry. Wait until the fish are at least ½ inch long before using this staple fry food.

Even though 10 new fish may not seem like a lot, Otocinclus can produce several cycles of eggs each year. Normally, this would be a lot of fish for a home aquarium keeper.

That being said, the toll of the pet fish industry on the wild populations is likely to be very high. This is made worse by the fact that many fish do not even live long enough to make it into a home tank. Once in the home tank, most do not live past one month.

If you are able to successfully breed Otocinclus, it is one of the few species that you might have some luck selling to pet stores, including chains.

You may also have an easier time selling them in your local neighborhood or online. This, however, can be very expensive, and you will need to learn more about preparing the fish for shipping.

Nutritional Needs

In a natural setting, Otocinclus feed mainly on algae and other slime that builds up on rocks and plants. Contrary to popular belief, these fish are not herbivores.

They enjoy feeding on tiny crustaceans, protozoa, and scraps of flesh from animals and fish.

Best Sustenance Food TypeSinking algae wafers and catfish pellets
Additional Foods for Optimal HealthFrozen brine shrimp, tubifex worms, zucchini, and cucumber.
Special Foods and Considerations for Best Color and GrowthFeed live or frozen foods.
When and How Often to Feed Fish Based on Life CycleFeed adult fish once per day. If you include vegetables or frozen food, be sure to pick up any remaining food within 6 – 8 hours to prevent ammonia surges.

Finicky Fish Management: Start off by making sure the water chemistry is correct. This is also a good time to check ammonia, nitrite, and nitrate levels.

If the water chemistry is ok, pay attention to the other fish in the tank. Look for signs of bullying that may need to be addressed so that the Otos feel safe.

Failing that, try freeze dried plankton and live brine shrimp, especially if you have been feeding only staple foods. You can also add medicated foods that are safe for catfish and related species just in case the fish is coming down with an illness.

otocinclus in fish tank

Common Diseases and How to Avoid and Treat Them

Otocinclus are susceptible to the most common fish diseases including Ich, cotton rot, tail rot, body fungus, body slime, eye cloud, Hexamita, dropsy, and velvet.

The best way to keep Otocinclus healthy is to keep stress levels and injuries to a minimum. Make sure the water chemistry is correct, and avoid changing it as much as possible.

Keeping Otocinclus away from aggressive fish will also go a long way towards preventing injuries that infections can use to attack the fish.

The most common disease for Otocinclus is malnutrition.

Many aquarium keepers figure that the fish will simply live on algae or bits of food flakes that find their way to the bottom of the tank.

Otocinclus have specific dietary needs that may not be met using these resources. It is best to provide them with a sinking wafer or pelleted food that will meet their needs.

Best AntibioticDepending on the disease, you may have to choose between different antibiotics. No matter whether you are trying to treat Ich, body rot, or some other disease, always follow up with something that will work on Velvet. This is a very common and subtle secondary infection that usually requires a different antibiotic than the one used for the primary infection.
Treatments to AvoidNever use antibiotics that are not certified safe for catfish and related species.
Food Recommendations When SickMedicated foods for possible secondary internal parasitic infections. Most, if not all fish will arrive in your home with low level infections. These diseases will not show up unless something weakens the fish to the point where the pathogen propagates fast enough to cause symptoms. Using medicated foods is one way to ensure you stop internal parasites that will take advantage of the fish’s weakened state.
Hospital Tank or Isolation Within the Community Tank SpecificsThis is truly a judgment call. Otocinclus don’t do well with water chemistry and setting changes. On the other hand, they need a lot of live plants and other materials in the tank that can blunt the effectiveness of antibiotics.
If you have other species in the tank that can better tolerate water chemistry changes, I recommend moving them to a hospital tank. You can also try moving Otos into a hospital tank using water from the main community tank. This is one of the few places where I recommend using silk toys are well made plastic caves that Otos can hide in while they are recuperating.

3 More Things You Should Know About Otocinclus

  1. When Otocinclus go to the top of the tank, they are able to breathe some room air.
  2. If you purchase Otocinclus locally, choose ones that look like they have a full belly. Avoid fish that look bloated, as this is a sign of disease.
  3. Always quarantine Otocinclus for at least 1 month before moving them into a community tank. During this time, keep adding water from the community tank into the quarantine tank so that the transfer will be less stressful.

Otocinclus are a useful and fascinating fish to have in community tanks. If you are looking to get into fish breeding, they present a worthwhile challenge. Since most Otocinclus are wild caught, being able to breed them in captivity will ease the burden on native populations.

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