Otocinclus – Detailed Guide: Care, Diet, and Breeding

Otocinclus Catfish is a very peaceful fish with a huge appetite for algae. They are also known for pacific temperament and excellent cleaning skills.

Although Otocinclus might seem a perfect member of the algae-eating team and clean-up crew, there is a little more to its care than that. These small catfish require some pretty specific care, especially for a new tank.

It is pretty understandable that these cute little fish can charm anybody. However, I would not recommend Otocinclus fish for beginners as they can also be a challenge to keep alive.

In this guide, I will share some practical tips and take you through everything you need to know on how to take care of them and should you choose Otocinclus as your fish.

Quick Notes about the Otocinclus

Name	Otocinclus Catfish
Other Names	Otos, Ottos, Dwarf suckers, Oto cat, Dwarf Suckermouth, Dwarf Sucking Catfish, and Midget Sucker Fish
Scientific Name	Otocinclus sp.
Tank size (minimum)	10 gallons (~40 liters)
Keeping	Medium
Breeding	Difficult
Size	4 – 5 cm (~1.5 – 2 inches)
Optimal Temperature	23 – 27 °C (73 – 80 °F)
Optimal PH	6.5 – 7.5 (6.0 – 7.5)
Optimal GH	4 – 12
Optimal KH	3 – 10
Dwellers	Mid and bottom
Nitrate	Less than 20
Diet	Algae eater / herbivore
Temperament	Peaceful
Life span	up to 7 years
Color Form	Olive-brown, black and white

Natural Habitat of the Otocinclus

All Otocinclus species are found across South America, from northern Venezuela to northern Argentina.

They usually inhabit small streams or shallow rivers and often associated with densely vegetated waters. Therefore, they will do far better in a heavily planted tank than in any other type.

Description of the Otocinclus

This is a very small fish. They can measure between 4 and 5 centimeters (1.5 – 2 inches) in length and have an elongated shape, rounded on the back and flattened ventrally.

The head is slightly flattened, with the eyes on either side, giving Otocinclus lateral vision.

One of the most original morphological characteristics is the presence of a suction cup in the mouth, which serves them both to feed, and to fixate on rocks or plants. This is very useful in their natural habitat of rivers with currents.

They typically live 3 to 7 years with appropriate care. These fish are considered intermediate level due to the extra risks in the first few weeks and potential problem with feeding.

Otocinclus Species

Currently, the genus Otocinclus contains 19 species of freshwater catfish. Although they have many different small morphological characteristics (useful for scientists) the easiest way for us is to look at colors and patterns.

For example, the most popular species in the aquarium hobby are:

• Common Otocinclus (Otocinclus vittatus) has a very defined black to brown lines that run along the entire length of the body and into the caudal fin. The top is almost fully brown and the lower part is white.
• Otocinclus macrospilus looks very similar to Otocinclus vittatus. The main difference is that its sidelines do not reach the caudal fin. In addition, some Otos of this species have yellowish body thus are often called the Golden Otos.
• Zebra Otocinclus (Otocinclus Cocama) is hard to confuse. The name tells for itself. This species has vertical black and white stripes.

Some species are extremely rare in the aquarium hobby. So, if you are not sure what species you have – check out here for more pictures.

Behavior of the Otocinclus

Otocinclus is a social fish. In nature, Otocinclus are generally found in large schools. In some cases, the schools can have hundreds or even thousands of fish. Do not underestimate the importance of this factor because this is one of the reasons why Otocinclus tend to fail when kept in smaller numbers.

Otocinclus are often just really shy fish. Even in the absence of the predators in the tanks, Otocinclus will not feel safe when they are in small numbers. For them, diminished numbers is a certain sign of danger, so they hide. As a result, they do not get enough food and, eventually, get stressed.

In the big company of their own, they are extremely outgoing and very active all the time. Otocinclus graze constantly on algae on all surfaces. In big groups, they are constantly visible and way easier to feed.

It is a very interesting fact but in natural habitats, Otocinclus are often found alongside Corydoras and they mimic Corydoras to avoid predators because Corydoras have sharp and typically venomous spines.

They are also diurnal and enjoy quickly swimming around the tank. However, when they feel intimidated during day time they can become more active at night.

Features:

• Social: Very
• Active: Yes
• Peaceful: Yes

Feeding Otocinclus

Otocinclus are herbivores. In the wild, they primarily eat algae and slime (biofilm) that builds up on rocks and plants. Therefore, it’s important to keep live plants in your aquarium to encourage algae growth and leaves for the biofilm growth. Slow growing plants such as Anubias, Cryptocorynes, and Java Ferns are all ideal plants to grow in your aquarium.

Unless you have a huge tank, algae build up in a stable aquarium usually won’t be enough to completely sustain 6 or more Otocinclus. Therefore, you should also be sure to feed them algae wafers or catfish pellets. It’s crucial for them to eat frequently, so food needs to be available almost all the time.

Some supplemental foods to give your Otocinclus may include blanched zucchini, spinach, peas, and cucumber. All vegetables added to a tank should be verified as pesticide-free because Otocinclus have no protection from chemicals.

Tip: It’s quite possible that you will have to try different vegetables before they find what they like. If you are given them peas, they must be salt-free. Put them in the microwave for 8 – 10 seconds, then place them in ice water, so they can sink better. Next, remove the shell and feed it to your Otocinclus.

Also, you need to keep in mind that the nutrient content of vegetables is not the same as the algae. Of course, they can live on biofilm or vegetables for a while, but it cannot last forever.

You should feed Otocinclus daily. All frozen foods or vegetables remaining after feedings should be removed from the tank within 6 to 8 hours to avoid ammonia surges. You do not want such things to rot if not eaten.

These little guys should have nice round bellies but not too big that it looks like it is going pop.

Features:

• Diet Type: Herbivore
• Food Preference: Algae
• Feeding Frequency: Daily

Read more “How to Blanch Сucumbers and Zucchini for Shrimp, Snails and Fish the Right Way”.

Otocinclus and Feeding Problems

Consider yourself very lucky if you Otocinclus can eat something other than algae! The problem is that often they do not learn to eat anything else but fresh algae. Therefore, feeding them algae wafers or even blanched vegetables, will not be a guarantee they eat well.

So what can we do in this case? Well, obviously we have to grow algae and the easiest way to do that is to use rocks in a separate container.

1. You need some kind of transparent container (large bottle, spare tank, etc.).
2. Fill it with water. Use the water that comes from water changes.
3. Put there a lot of small rocks like marble chips and ceramic filter media (The rocks should be clean and aquarium safe, of course).
4. Leave it under the strongest lighting you can find. Ideally – 24/7.
5. Use any fertilizer to grow plants in a tank.
6. Using an airstone will boost algae growth as well.
7. Once you see that rocks are turning green, take a few a place them in the tank to feed
8. Return the rocks to the container when they are clean.

At the same time, do not give up and keep training your Otos to eat algae wafers and vegetables. Give them time to learn that this can be a food source for them. For example, break one wafer into several pieces and leave them in their favorite places overnight.

There are some reports that Otocinclus really like Repashy Soilent Green (check the price on Amazon).

What Algae do Otocinclus eat?

They are great against: green spot algae, green dust algae, and diatoms/brown algae. So-so against hair algae. Otocinclus will not eat staghorn algae, red, or Black beard algae even when they are starving.

You can read more about algae and Otocinclus in my article “Types of Algae. Best Algae Eating Team”.

Are Otocinclus Plants Safe?

Yes, they are absolutely safe to keep in planted tanks. Otocinclus species have very small dentition meaning that they are not physically capable of damaging the vast majority of plants. Therefore, they really have no interest in eating plants, they only graze on the surfaces of them.

Keeping and Housing Otocinclus

I have to start off by saying that Otos are sensitive, and a poor choice for the first inhabitants. In addition, they are highly susceptible to tank changes and need extra attention in the first few weeks.

Before introducing your Oto’s, your tank should be cycled, fully established, and have algae growth for sustenance. To cycle your tank takes anywhere from 4 weeks to 2 months.

To start your cycle, drop fish flakes into your aquarium about every 12 hours. These flakes will decay, and Ammonia will be produced. Ammonia levels should be kept at least 3ppm for a week. Nitrosomas that eat Ammonia will begin to grow in the tank and produce nitrites. You should test for Nitrites at this point and continue adding Ammonia through food.

Eventually, the Nitrites levels will begin to drop. Test Nitrite and Ammonia for a few weeks. Then start testing for Nitrates. When Ammonia and Nitrite levels go back to 0, your cycle is complete. Nitrates should be below 40 and water changes can be done to lower the Nitrate levels.

You can also read my article “Step-by-Step Cycling your Shrimp Aquarium Fishless”.

Tank size:

As I have already mentioned, Otocinclus are a schooling fish and need to be in groups of their own kind. Therefore, despite their small size, the minimum tank size for Oto’s is 10 gallons (40 liters).

The general rule of thumb is at least 6 Otos but the more the better. However, in this case, you will need a larger tank. Keep in mind that there is a fine line:

• If the tank is too big for them, they can get scared and hide. They need to see their buddies in all places to feel safe.
• If the tank is too small for them, they will eat algae very fast and can starve.

Note: Because the fish prefer to stay at the mid and bottom of the tank, the tank should be long and shallow.

Water Parameters:

• Temperature: Otocinclus will thrive in warm waters that are consistently between 23 – 27 °C (73 – 80 °F).
• pH: Although they can take a wide range of pH (from 6.0 to 7.5), they still prefer pH a little bit on the lower side 6.5 – 7.0.
• Hardness: Neutral to soft water being ideal for them.

Substrate:

The best substrate for the tank is soil, sand, and smooth gravel. Sharp gravel should be avoided because it can injure the fish.

Aeration:

Preferably, the water should be slow-moving with high oxygen levels. You can use soft flow air stones to increase oxygen levels.

Plants and Decorations

They thrive in planted tanks that have good water quality. Barely decorated tanks without live plants will be very stressful and unpleasant for Otocinclus. So, success keeping them is less likely in such tanks.

The ideal habitat will also have rounded rocks, driftwood, and/or caves to hide in.
Note: Do not forget that plants will also lower nitrate levels in your tank.

You will definitely need appropriate LED lighting for the plants and algae to grow. Read more information in my article “Advanced Guide to Planted Tank Lighting”.

Filtration

Adequate filtration is very important no matter the tank size. Although some people prefer to use a canister filter to get the best filtration. Personally, I would recommend a Matten filter (or sponge filter). The point is that these filters have a very large surface area where Otocinclus can feed on.

Your nitrate levels should be between 0-20ppm (parts per million) and have no measurable ammonia or nitrite.

You can read my article to learn more about it “The Best Filtration System for Breeding Shrimp”.

Copper

Otocinclus are very sensitive to copper. Do not use and avoid medication, or plant fertilizer that contains Copper of any form. Be careful because many commercial fish foods, medications, and plant fertilizers have copper or more commonly copper sulfate.

According to the experiment, most Otocinclus population died within 48 hours at 0.575 mg/l Copper sulfate concentration.

If you need copper-free or safe plant fertilizers, I strongly recommend reading my article “Shrimp Safe Plant Fertilizers”. Dwarf shrimp are even more sensitive to copper than fish.

Acclimation and Quarantine

Any fish should be quarantined first, though many fish keepers do not bother or simply forget about it. Do not be like them, this mistake can have a very high price.

You must isolate the Oto’s in order to prevent the potential spread of disease into your tank. This isolation should last for a few weeks. The fish should then be transferred into the main aquarium using the drip acclimation method (read more about it here). 

Unfortunately, the problem with Otocinclus species is that they do not do very well in a small and bare quarantine tank. Therefore, add there at least some mosses. However, what is even more important – the quarantine tank should also have a lot of algae. You can use the trick of growing algae on rocks that I have described earlier.

Be careful with chemicals like copper (read more). Fish, crabs, shrimp, and crayfish do not tolerate copper-based medications.

Basic Tank Equipment (links to check the price on Amazon) Filter: Sponge filter, Matten Filter. Aquarium pump: Tetra whisper Air pump  Active Substrate: ADA Aquasoil, Fluval Plant, Carib sea sand, etc. Decor: Malaysian Driftwood, PVC pipes, Coconuts, Decorations, etc.

Sexing Otocinclus

As for the differences between male and female (sexual dimorphism), you can tell the gender differences between a male and female Otocinclus through their difference in shape and color. Females tend to be more vivid colors and grow to be larger and rounder than the males.

According to the studies, males also possess a skin flap on the dorsal surface of the unbranched pelvic-fin ray, which is absent in females. Finally, males have a small contact organ formed near the fin base.

Mating Otocinclus

If you are breeding, you should choose a couple that has features and markings that you would want passed on to the offspring. Separate the male and the female from the other fish. Otocinclus do not typically mate easily but a high protein diet can influence your fish into mating. Daphnia, algae wafers, and brine shrimp are all excellent food choices when you wish to breed your Otocinclus.

Your mating tank should be at least 80 liters (20 gallons) to be able to hold all the soon-to-be-born fry. Otocinclus lay eggs all around the tank on plants. If you are looking to breed, you should have aquarium plants in your breeding tank.

Water parameters are also essential to a successful breeding. The temperature in the breeding tank should be warm. The tank should be 78.8-degree Fahrenheit or 26 degrees Celsius which will encourage your fish to breed. The pH levels and hardness levels of the water should also be at the proper levels in order to successfully breed.

Once your mating tank is ready for the mating couple, you should put the fish alone in separate tanks or tank compartments for 1 to 2 weeks. After at least 1 week has passed, you can introduce your couple into the mating tank and hope for the mating ritual to begin.

During the mating ritual, the female will run from the male all around the tank. The male will chase after the female. Eventually, the male will catch up to the female and the mating process will start. The couple will assume a T-shaped position. The female will lay her eggs in the tank and the male will fertilize them.

Breeding Otocinclus

According to the studies, Otocinclus become mature at 25 mm (1 inch) long. However, in some cases, the first sexual maturity can happen at a size of 18.7 mm for females and 20.1 mm for males. Every female can have from 16 to 202 eggs, depending mainly on female size.

Tip: If you shine a light on it in the dark you should be able to see them if it has eggs.

Otocinclus do not care for their eggs. Once they lay them, they leave them.

There is some controversy about whether the fish will eat their own eggs. Some aquarists even say that it may be best to remove the mating couple from the tank after the eggs have been laid and fertilized. The eggs should hatch and begin their lives as fry after a few days. The fry eat algae and microbes.

Potential Problems Associated with Otocinclus

Most issues with Oto are due to an unclean tank and a poor diet. If your fish are sick, you can tell by a change in appetite, inactivity, or increased respiration. The fish may also change colors and produce spots.

Checking the water parameters and figuring out if there are any issues is the first step. Fixing the problems can get your fish back to normal. If your fish are experiencing a change in appetite, changing their diet may also help.

Huge belly: Either a swim bladder problem or an internal parasite. You need to put the fish in a quarantine tank.

Otocinclus and Suitable Tankmates

Otocinclus are super friendly little fish. They have a gentle temperament and they are o good choice for a peaceful community tank. Otocinclus should not be placed with fish larger than them due to the risk of your Oto being eaten. Oto should also not share a tank with tank mates that share an aggressive temperament because you may find your Oto wounded.

They tend to ignore other fish entirely unless they are big enough to scare them, in which case they hide.

Fish

All tank mates should have a gentle temperament and enjoy the same water parameters as the Otocinclus.

Some compatible tank mates are Pygmy Cory, Boraras, Panda Garra, Dwarf Gouramis, Albino Bristlenose Pleco, Royal Farlowella, Neon tetras, Harlequin Rasboras, Ruby Tetras, Dwarf Ember Barbs, Guppies, Endlers, Medaka Ricefish, and Rasbora.

Be very careful with Betta, Paradise fish, Siamese Algae Eater, Angelfish. They are like every species; some are more aggressive than others.

Some tank mates to avoid are Cichlids, Goldfish, Jack Dempsey, and Oscars. They should never be placed in a tank with Otocinclus.

Shrimp

Otocinclus is the only fish in a community tank that is absolutely safe to keep with shrimp. They do not have any interest in eating shrimp, they will never attack or harass even baby shrimp.

The only problem is that they will compete with shrimp for algae thus it can affect the survival rate of baby shrimp. So, if you are planning to seriously breed shrimp, you cannot allow any fish in the tank! Even if it is an amazing Otocinclus.

In addition, if there are not enough algae in the tank, it can be difficult to keep Otocinclus and Amano shrimp. As an algae eating-team, they are absolutely awesome but Amano shrimp are voracious algae eaters and in the long run, can starve Otocinclus out.

Snails

Otocinclus are compatible with any freshwater snail. Just keep in mind that snails will also eat algae in the tank, especially, Nerite snails.

Nerite snails have absolutely the same diet as Otocinclus and will also starve without algae.

Crayfish and Crabs

Absolutely not! Keep them away from all types of crayfish and crabs. They can and will try to catch Otocinclus whenever it is possible.

Buying Otocinclus

If you buy Oto’s from a pet store, there is a likely chance that they will die immediately. The transit to the pet store is hard on fish. Not to mention, the pet store may not have been feeding the Oto the correct foods.

Sad fact: Do you know that almost all Otocinclus are wild-caught? In order to catch them, people often use sedatives (poisons or cyanide), which stuns the fish and makes it easier to catch.

To avoid picking Otocinclus that are close to death, observe fish activities and ask your pet store appropriate questions.

1. Asking how long the Otos have been in the pet store can be a good indicator of if the Oto will live or not. If they just got the Oto in, they will likely be stressed and possibly starved from the transit. If they have been there for a few weeks and seem to have acclimated well, chances are that they are in good health and will be more likely to survive their transition process into their new home tank.
2. Another great question to ask your pet store is what they have been feeding their Oto. If they say flakes, then they have been feeding the Oto the wrong food and they will likely get sick or die. If the store can’t answer, then that is also a bad sign.
3. Ideally, you need to see their behavior during feeding. They should latch algae wafers/ tabs with their little sucker mouths.
4. Check their general activity. Do not buy Otocinclus if they do not move much and sit quietly on the bottom. This is a very bad sign in a fish that is usually pretty active.
5. To judge the health of an Oto, look at their bellies. If their bellies are plump, then that is a good sign. However, if their bellies look unnaturally bloated then that may be a sign of a bacterial infection.
6. Check out their mouths. They should not be injured.
7. Color can also be a good sign of a healthy Oto. You should look for Oto’s that are olive-brown, black and white.

The best place to get an Oto is from a reputable breeder near you so that you know how your Otos have been treated although that is not always possible. You can also buy Oto online, even on Amazon.

In Conclusion

The Otocinclus have intermediate care needs. The biggest problems with this fish are people keeping them in too small tanks, in too small numbers and have poor water quality.

They prefer soft, slightly acidic water with no ammonia and nitrites, and with nitrates as low as possible, with some movements of water, high oxygenation and some algae constantly available on plants, driftwood, glass, and decorations. These are keys to success.

The first few weeks of caring for Otocinclus are critical. After the first few weeks, the Oto will begin to adjust to the tank. However, they are still vulnerable to parameter changes so the tank levels should be closely monitored. Oto may be difficult to raise by new aquarium hobbyists, but experienced aquarists should be fine.

References:

1. Determination of medium lethal concentration (LC ) produced by pentahydrate copper sulfate in ten species of freshwater fish bioindicators used in Perú Ciencia y Desarrollo. Ciencia y Desarrollo. Universidad Alas Peruanas.http://dx.doi.org/10.21503/cyd.v22i4.1837
2. Otocinclus tapirape: A New Hypoptopomatine Catfish from Central Brazil (Siluriformes: Loricariidae). Copeia 2002(4):1063-1069. 2002 DOI: 10.1643/0045-8511(2002)002[1063:OTANHC]2.0.CO;2
3. Otocinclus batmani, a new species of hypoptopomatine catfish (Siluriformes: Loricariidae) from Colombia and Peru. Neotropical Ichthyology. 2006. DOI: 10.1590/S1679-62252006000400001
4. Otocinclus cocama, a new uniquely colored loricariid catfish from Peru (Teleostei: Siluriformes), with comments on the impact of taxonomic revisions to the discovery of new taxa. Neotropical Ichthyology. 2004 DOI: 10.1590/S1679-62252004000300001
5. Reproductive ecology of Otocinclus vittatus (Regan, 1904) in the Pantanal floodplain, upper Paraguay River basin. Brazilian Journal of Biology. 2018. https://doi.org/10.1590/1519-6984.191560