Common Names: Otocinclus Catfish, Otto, Oto
Scientific Name: Otocinclus sp
Minimum Tank Size: 30 Gallons
Care Level: Easy
Max Size: 2 Inches
Temperature: 74-80 F
Tank Level: Middle
Otocinclus Catfish: Species Overview
For many aquarium enthusiasts, the otocinclus catfish is a highly desirable addition to their established tanks with live plantings. These small, schooling fish are popular, relatively easy to keep, and inexpensive in most fish supply stores.
They might not be ideal for novice fish keepers because they require a bit of finesse to keep well-fed and hate changes in their environment.
They have a reputation for being challenging to keep healthy, but with some know-how and consistency, you can add these helpful, plant-cleaning, and algae-munching fish to your tank.
They’re common in a handful of certain species that make up the bulk of otocinclus catfish sold. But there are more exotic ones that have outrageous colors and are sometimes harder to find. When looking for otocinclus catfish, remember they may go by a shortened version of their name, Oto.
There are around twenty common otocinclus catfish species in total, and a few are popular for keeping in home aquariums. Their specific colorings can vary considerably by species. Some are harder to find and more expensive than others.
The otocinclus catfish is a relatively small fish with a narrow body and short fins. They have a protruding, large mouth with powerful suction that aids them in consuming their favorite meals of vegetables and algae. When they puff their lips out, they can attach them to surfaces, anchoring themselves in place.
Almost every species of the otocinclus catfish sports a brown stripe that runs latitudinally along their body, though the color, shape, and thickness can vary quite a bit. They often have a double tail with a clear separation between the top and bottom section, and typically the fins of an otocinclus catfish are nearly translucent.
In addition, all species of otocinclus catfish share an identifying trait that adds to their distinctive appearance.
When you look closely, there are pronounced rows of scales that look like armor plates laid across the top of the fish’s body. This tough armor offers protection from rubbing against rough surfaces while swimming in search of food. It can even help prevent attacks by other fish.
Even though there are a few varieties of otocinclus catfish, their care is pretty similar regardless of their specific genealogy. But, since there are so many species of these diminutive, colorful fish, it’s a good idea to make sure you know the color patterns that identify them.
Most Kept Otocinclus by Species
Here’s a quick breakdown of some of the most popular Otos. They share similar profiles, but their coloring and striping can help identify different species at a glance.
The common oto is probably the most widespread in nature. It has a splotchy or speckled pattern on its back and sides, with a brilliant white underside. They have a distinct, brown stripe from the head to the caudal fin, which may be part brown.
The other fins are nearly translucent. Since they’re the most common, they are usually the least expensive in the store.
The dwarf oto is easily mistaken for a common otocinclus, as it has a very similar brown stripe along its midline. However, the brown stripe ends before it reaches the fin itself, and the caudal fin is translucent.
The dwarf otocinclus also usually has a roundish spot of color on its tail, and the rest of the fins are translucent.
Perhaps unsurprisingly, the zebra otocinclus has vertical stripes of black and white. The alternating bands of color start just behind the fish’s head and continue along the body until they reach the caudal fin. There are also usually horizontal stripes along the head.
Individual fish have variations in the uniformity of the stripes. Some stripes may be a bit blurry, while others are very sharp. Accordingly, some keepers refer to this species as a tiger otocinclus.
The silver oto has a similar appearance to the common oto. But, the brown color variations are lighter and tend to be more silvery in appearance.
Gold (or Golden) Otocinclus
The gold otocinclus is very similar to the common oto, but its coloring is much more yellowish or golden and shimmery.
Various Other Species of Otocinclus
Other species of otocinclus catfish include
- Giant otocinclus – twice as large as common otos with gray or mottled brown coloring.
- Alligator otocinclus – a rare species of oto with a mottled appearance and gray, black, and brown colors.
- Hoppe’s Otocinclus – A golden fish with a heavy dark stripe along its middle and a prominent spot near its tail
- Peppered Otocinclus – A fish with a speckled appearance and a regular pattern of brown, black, gold, and orange.
There is a bit of debate about exactly how many species of otocinclus catfish there are. Popular opinion places the total number of species between nineteen and twenty-two.
If you’re looking for otocinclus catfish in the store, don’t be surprised if you find them under one of their other common, popular names. Some shops may have signs like otocinclus, dwarf sucker, dwarf armored catfish, plain oto, oto cat, and otto. But if you’re looking for specific breeds, look for more specificity.
Otocinclus Impostors: Chinese Algae Eaters
When browsing a store for otocinclus catfish, be alert to a fish that has a similar appearance but can become a major headache to aquarium keepers.
The Chinese algae eater also has a midline stripe, and when young, they are of the same size and shape as otos. But unlike any species of otocinclus catfish, the stripe on a Chinese algae eater is intense, rich, and black. It also has yellow shading at the edges of the stripe, and they lack the distinct armor-like pattern on their dorsal side.
Make sure you’re alert to the differences because you don’t want to inadvertently introduce Chinese algae eaters to your home aquarium.
As they grow, they become much more aggressive, and they can even begin to suck algae off of other fish. They also quickly outpace the development of the oto and grow much larger when they reach maturity.
If you don’t notice your mistake in time, you can end up with a giant, 10-inch-long Chinese algae eater and a tank full of dead tankmates.
The otocinclus catfish is native to the waters of South America, where it resides in slow-moving streams and relatively calm, shallow rivers. The otocinclus catfish is rarely found in the Orinoco or Amazon lowlands, but they are quite common in the East of the Andes mountains, from Argentina to Venezuela.
They are often found with their powerful mouths attached to sturdy rocks, driftwood, and plants, while they eat their favorite meal of algae. They also eat aufwuchs, which are the combination of bacteria, microbes, and settled detritus that coats natural underwater surfaces.
Their natural waters tend to feature abundant vegetation without becoming overwhelmingly dense. These fish thrive in areas that have plenty of plant life, in balance with ample open water, abundant sunshine, and a sandy, soft riverbed.
The most common plants found in these waters include broad-leaf grasses, tree roots, and plants that float on the top of the water a bit, offering plenty of concealment and shadow for fish below.
They do not live in brackish or salt waters.
The typical otocinclus catfish is less than two inches long. They fit into the nano-fish category, and many of the most popular species max out at about one inch in length.
Males tend to be smaller than their female counterparts, especially when viewed from overhead. If you look down at a school of otocinclus catfish, you can pretty easily determine all their sexes.
The typical lifespan of an otocinclus catfish is from three to five years. However, these fish have a bit of a reputation for being hard to keep alive.
Their perceived finicky health and short lifespans aren’t usually the fish’s fault, though. Most often, the tank they are kept in either doesn’t provide enough food or the water conditions have become too rich in nitrates and ammonia.
Otocinclus catfish do not tolerate deteriorating tank conditions. Stay alert to darkening or duller colorations or a lack of vibrancy in their scales, as this can be a sign of distress due to poor water quality.
The easiest way to separate otocinclus catfish by gender is by comparing their size. Females look plumper and larger, especially when looked at from above.
Fish of both genders develop a more vibrant coloring when breeding. This temporary bolder coloring is thought to be a way to attract their mates.
The otocinclus catfish is a reliably peaceful addition to any aquarium. They are rarely aggressive and tend to be reclusive. Otos will quickly swim across a tank in search of a hiding spot whenever they feel threatened. Anything that implies danger, like a sudden dark shadow, will send them flashing through the water.
Unlike territorial fish, these algae eaters thrive in schools, even in smaller aquariums. They tend to be most active at night when they can be seen sucking on gravel, glass, plants, and decorations in search of algae. They may appear stuck onto objects as they latch to surfaces and feed.
You may even see a group of otos in a cluster as they graze on algae pockets. They are peaceful and shy by nature, so you can rely on them to avoid conflict. They thrive in small schools of other otos and are most confident when they are in a group.
There are no major differences in temperament between male and female otos. But, at breeding time, males may be seen chasing females, though there is no aggression.
The principal reason fish keepers consider otos an intermediately difficult fish is its sensitivity to poor water quality. Deteriorating tank conditions have a quick and drastic negative effect on their health.
Only introduce otos to a stable, established tank environment with plenty of food available.
Minimum Tank Size
Otos do best in tanks that mimic their natural habitat. There should be enough space for them to swim in open, sunny water at the top. There also needs to be an abundance of vegetation at the bottom of the tank and other hidden nooks for them to relax in.
So, even though they’re fairly small fish, you’ll need a minimum tank size of ten gallons for a group of six. Since these fish thrive in schools, many oto enthusiasts recommend starting with a group of at least ten.
Ten otos in a ten-gallon tank won’t take up much room, but they will interact with the environment throughout, and they may eat up all of the available food quite quickly. So, you want to increase tank size accordingly.
If you have more than ten otos, you should step up to a twenty-gallon tank, at minimum.
In general, otos like slow-moving, fresh water. Your tank should offer an oxygen-rich environment with a mild current.
For the best results, keep your otos in water that is from 72 to 79 degrees Fahrenheit (about 22 to 26 degrees Celsius).
Otos do well in relatively neutral water. Keep your tank’s pH in a range from 6.8 to 7.5 for the best results.
Otos do not like brackish or salt water. They do well when the water hardness is in the range between 7 and 15 degrees of general hardness (dGH). If you have very hard tap water, you may need to find another source for filling your tank.
The more your tank setup mimics the natural habitat of the oto, the more these schooling, passive fish will thrive. It’s essential that you develop the tank’s ecosystem prior to introducing any fish, especially otos.
Otos don’t tolerate poor tank conditions well. They have an undeserved reputation for being tough to keep alive, but if you stick with these parameters, you’re setting yourself up for success.
All otocinclus catfish like relatively soft and sandy substrate. Their quest for algae to eat may see them pushing their sucking mouth into the sand as they try to extract every bit of their food.
Harder substrates don’t work as well for them, and you should also avoid anything with rough, sharp edges, like gravel.
In a tank with otocinclus catfish, you want to offer plenty of room for these shy fish to hide. Caves, rocks, and driftwood do the job well but make sure there is enough room for plenty of live vegetation. Don’t overcrowd the tank because your otocinclus catfish will also need ample room for free swimming and exploring.
Plant life is an essential part of an otocinclus catfish tank. Staurogyne Repens is an ideal planting for otos, as it provides some room for concealment and grows into an expansive carpet across the bottom of the tank. Plus, it extracts harmful nitrates from the water and also adds oxygen, two things that otos require.
It’s also easy to propagate, hardy, and grows slowly, making it easy to maintain. Other plants you may want to consider include:
- Crypts (especially Cryptocoryne wendtii) are pretty much ideal for a tank with otos. You can find it in various colors that match your decor, and it’s relatively easy to care for.
- Amazon Sword (Echinodorus sp.) has dense, broad leaves that offer the ideal hiding place for otos. Once you have a strong, established set of Amazon sword plants, look for your otos to shelter under the leaves close to the bed of the tank.
- Java Fern (Microsorum Pteropus) is commonly available in aquarium stores. These popular plants are easy to maintain, and their long leaves offer not only a surface for algae to grow on but concealment for your school of otos as they dart about the tank.
- Anubias (especially Anubias barteri) also have broad leaves. There are a few varieties that will work well with otos, especially if you can find one that grows pretty large, as some have short leaves that won’t offer much concealment. Anubias also tend to be easy to care for.
Oto catfish don’t really need special supplemental lighting. A simple aquarium light on a timer that shuts it off at night and turns it on during the day is adequate. But to aid in the growth of algae, keeping your tank in a location that gets exposure to natural sunlight daily is ideal.
If you have a natural light source that hits your tank, ensure it doesn’t overheat the water. If you’re getting a ton of direct sunlight throughout the day, you may need to temper it with a shade or a curtain for part of the day.
Since otocinclus catfish are very sensitive to poor water quality, you need a reliable filter that removes nitrates and ammonia. Your filter media should be able to handle this on its own, without creating such a strong current that it disturbs your peaceful, calm otos.
You can also add additional natural filtration with live plantings that also help to remove nitrates and introduce oxygen. Bubblers and air stones aren’t strictly necessary, but they can be beneficial if they help create an oxygen-rich environment.
While otocinclus catfish don’t need water above 79 degrees Fahrenheit, they won’t tolerate water that’s below about 72 degrees very well. So, a heater is pretty much essential.
Otocinclus catfish are vegetarians. In the wild, they roam in packs, voraciously consuming algae and the slimy deposits of bacteria, organic matter, and detritus that coats things underwater. This biofilm, also called aufwuchs, will occur naturally in your tank.
But, it’s pretty much essential that your tank has as many broad-leaved plants as possible. The odds of successfully raising and keeping otocinclus catfish drop without them, as their surfaces collect the food that otocinclus catfish prefer.
You must provide an abundance of algae for them to eat. Doing so can be difficult, especially if you have a lot of hungry otos, so you can supplement their feeding with daily algae tablets. However, don’t be surprised if your fish are not inclined to eat the tablets. The tablets are unnatural, and the fish may not figure out what to do with them, even when they’re hungry.
When it seems like algae are in short supply, the best move may be to provide your otos with some supplemental food in the form of blanched vegetables, like lettuce, spinach, green beans, and zucchini.
To do so, boil the vegetables in water until they turn very tender. Then submerge them in cold water. Drain them, and put a handful in your tank. Since otos tend to graze, instead of feeding in a frenzy, there isn’t much risk of overfeeding.
Then, about 24 hours later, remove any of the vegetables that haven’t been eaten yet.
Providing a sustainable diet for your otos is among the highest hurdles to keeping them healthy. Keep alert for changes in their behavior or appearance that may indicate poor nutrition.
This practice also applies when you’re shopping for your otos. Commercial suppliers may not always provide ideal tank conditions in their stores. So if it seems like some of the otos are much bigger than the others, you should look to buy the bigger ones, as they have been fed better.
In general, otocinclus catfish reach their breeding age between six and nine months. You can stimulate breeding activity by warming the tank to a temperature slightly over 79 degrees. It’s also thought that a protein-rich diet and especially clean water can help encourage breeding.
During breeding, the males can be seen chasing the females around the tank. The females eventually lay eggs on surfaces like plants and driftwood, and the males swim by to fertilize them. Several days later, the eggs will hatch, and the fry will begin eating bacteria and algae, just like their parents.
But the process is so rarely successful in captivity that only pros attempt it.
Breeding otocinclus catfish in captivity is immensely difficult. Even commercial breeders are often unsuccessful. So, most otocinclus catfish come from natural waters, where they are captured for sale.
This practice of harvesting fish from their natural habitat often involves unsavory methods that may include using poisons to stun the fish. Be alert to signs of malnutrition when shopping for otocinclus, as small, skinny fish with dull colors indicate that they have had a rough journey to the store’s tank.
Otocinclus catfish are susceptible to common diseases that affect freshwater fish, especially Ich. Ich (also known as white spot disease) is a parasite that latches onto otos, causing itchy spots on their fins and body.
If a fish is afflicted with Ich, you may notice it trying to scratch its body on rough surfaces by swimming up against them. You may also notice a decrease in overall activity and energy.
The best way to treat Ich is by quarantining the affected fish as quickly as you can and then adding a commercial treatment that kills the parasite. Maintaining good water quality can aid in the prevention of Ich and other freshwater diseases.
Potential Tank Mates
Otos are peaceful and tend to dwell on the bottom of tanks. Their ideal tank mates are similarly calm and averse to conflict. Just make sure that you don’t choose fish that will also compete for algae, as their feeding may leave your otos hungry.
The best tankmates for otos include bettas, danios (especially the celestial pearl and galaxy rasbora varieties), Endler’s livebearers, and chili rasbora. Each of these fish is fairly small and will mostly keep to themselves.
Some bettas might be very energetic and occasionally chase an oto, but they are unlikely to become aggressive or injure them. Shrimp and some freshwater snails can also make good tank mates.
A list of suitable cohabitors for your otocinclus catfish tank looks like this:
- Dwarf gouramis
- Cherry barbs
- Zebra loaches
- Nerite snails
- Ghost shrimp
- Amano shrimp
- Malaysian trumpet snails.
Since they are most confident and energetic in bigger schools, sometimes adding more otocinclus catfish to your tank is the best move!
As a general rule, don’t add any predatory fish with a mouth big enough to catch an oto!
Otocinclus catfish have an undeserved reputation for being especially finicky. If you buy healthy, well-fed fish, and you maintain your tank conditions to their liking, they are easy to keep and offer a lot of entertainment as they search for food and consume their meals.
Since they tend to hang out near the bottom of the tank, they’re ideal for tanks with other small schooling fish that like to congregate near the top. This way, everyone has room to swim freely without getting in each other’s way.
The biggest warning to anyone considering adding otos to their aquarium is that you must have an established, veggie-rich tank ready to go. If you do, add some otocinclus catfish today!