Freshwater Fish · Catfish

Otocinclus

Otocinclus vittatus

Small algae-grazer for mature planted tanksIntermediate

Lifespan: 3-5 years
Size: 1.2-2 in
Social needs: Social shoaler - keep 6+ together
Time: Moderate (daily feed, stable mature tank)
Cost: Low-Medium
Diet: Herbivore (algae/biofilm grazer)

Overview

What is this animal?

The Otocinclus, or oto, is a small suckermouth catfish from South America and one of the better genuine algae-grazers for the planted community tank.
It works over leaves and glass, removing soft algae and biofilm too delicate for larger plecos.
Several look-alike species are sold simply as otos, commonly O. vittatus, O. macrospilus and O. vestitus, and they need the same care.

Its intermediate rating is well earned: most otos die not because they are hard to keep but because they are sold half-starved, often wild-caught, and rushed into immature tanks before there is enough biofilm to sustain them.

Temperament

Otocinclus are peaceful, gentle shoaling fish that feel secure and graze openly only in groups of six or more.
Singly or in small numbers they hide and stress, so a true shoal is essential for natural behaviour.

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They are harmless to tankmates and well suited to planted communities of 24 gallons or more alongside small tetras, rasboras, shrimp, and corydoras.
Keep them away from boisterous or large fish, which intimidate these small grazers.

A good fit for

Mature, algae-rich planted tanks
Peaceful planted community tanks of 24 gallons or more
Keepers wanting safe algae control on plants
Aquarists who select round-bellied stock

Common mistakes to avoid

Adding to a new tank with no algae/biofilm
Buying thin, starved, hollow-bellied stock
Keeping fewer than 6 (they shoal)
Salt/copper medications they tolerate poorly

Enclosure

Minimum 24 gallons, for a group of 6

Cannot be kept alone. The minimum is 6, and the space above is for that group.

Keep a shoal of six or more in a well-established, fully cycled tank of at least 24 US gallons and 24 in long, with a stable, mature growth of algae; a 29-gallon tank qualifies, and a 20-gallon long tank falls short on volume.
Maintain 72-81°F, pH 6.0-7.5, and clean, well-oxygenated water with low nitrate.

Never add otos to a brand-new tank; they need an aged setup with soft green algae already growing.

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Provide plants, driftwood, and gentle flow.
They are highly sensitive to ammonia and nitrite, so the cycle must be solid before they arrive.

Check your enclosure

Supplies

Setup

Tank and stand
Filter
Heater and thermometer
Substrate, plants and decor
Liquid test kit
Dechlorinator and starter supplies

Ongoing

Sinking pellets, wafers or tablets (corydoras)
Algae or spirulina wafers (bristlenose and otocinclus)
Frozen bloodworm, daphnia and brine shrimp (corydoras)
Untreated aquarium driftwood (for bristlenose plecos to rasp)
Courgette, cucumber and spinach for blanching (bristlenose and otocinclus)

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Veg clip or a stainless veg skewer (bristlenose and otocinclus)
Feeding tongs or a pipette for target-feeding
Fine sand substrate for corydoras foraging

Safe substrate: Fine, smooth sand · Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras) · Bare bottom (quarantine and grow-out only)

Work out the cost

Care routine

Daily

Check temperature and equipment
Head-count and look everyone over
Sinking food at lights-out

Every few days

Top up evaporationevery 3 days

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Weekly

Check belly profiles
Test the water
Water change and gravel vacuum
Wipe the front glass only

Every few weeks

Trim and thin the plantsevery 2 weeks

Monthly

Check supplies and reagent dates
Check the driftwood
Replace or recharge chemical media, if you use any (skip it in a blackwater tank)
Rinse the filter media

Health review: Quarterly bottom-dweller review, every 3 months

Tools

Is your enclosure big enough?Check your measurements against the recommended size What will it cost?Setup, monthly and over its whole life, itemised Is this ammonia reading dangerous?Works out the toxic part from your pH and temperature

Care in depth

Diet

Herbivore (algae/biofilm grazer)

Otocinclus are dedicated herbivores that graze soft green algae and biofilm.
In tanks with insufficient algae they will starve, so always supplement with blanched vegetables such as courgette, cucumber, and spinach, plus quality algae wafers.

Many new otos arrive emaciated and need immediate, reliable feeding to recover; a sunken belly is a danger sign.
Keep a steady supply of grazing food and vegetables.
They cannot subsist on commercial flake intended for other fish.

Health

Signs of good health, and the common problems

The biggest killer of otos is starvation, both before purchase and in algae-poor tanks.
Combined with their sensitivity to poor water and shipping stress, this makes the first few weeks critical.
Choose round-bellied, active individuals and acclimatise them slowly.

They tolerate medications, salt, and copper poorly, so treat with care.
Check belly shape at least weekly, and daily for newly bought fish: flat or sunken means underfeeding.
In a mature, stable, algae-rich tank with clean water they settle well and live several years.

Is this urgent?

6 warning signs and how fast to act, 3 of them right away

In a fish tank the patient is usually the water. Test before you treat: dosing a healthy tank for a disease it does not have makes things worse.

Go now

Any detectable ammonia or nitrite in a stocked tankLarge water change now with dechlorinated, temperature-matched water. Stop feeding. Test again in 12 hours. Both are directly toxic. How toxic the ammonia reading is depends on pH and temperature, so the same number can be harmless or lethal.

Now

Fish gasping at the surface with fast gill movement, or crowding the filter outflowIncrease surface movement now (gently in a betta or gourami tank, without creating a strong current), then test the water. Either the oxygen has crashed or the gills are being chemically burned. Both are hours-scale problems. Bettas, gouramis and corydoras rise to gulp air as part of normal breathing; the warning is constant gulping, fast gill movement, or the whole group hanging at the top.

Now

Sudden deaths, more than one fish in a dayTest ammonia, nitrite, nitrate and temperature before doing anything else. Do not add medication yet. Multiple simultaneous deaths usually point at the water or the equipment rather than a pathogen, so rule those out first.

Now

Today

Flashing: repeatedly scraping against decor or substrateTest the water, then look closely for parasites. Irritation is either chemical or parasitic; the test tells you which before you medicate.

Today

White salt-grain spots over the body and finsBegin the appropriate treatment today and check the temperature. The parasite's life cycle is temperature-driven, and it multiplies with every cycle you wait.

Today

Soon

Clamped fins, hiding, or refusing food for more than two daysTest the water and review recent changes. Usually the earliest visible sign of a parameter drifting.

A few days

Never add a new fish to a tank that is not fully cycled, and never treat blind. A test kit is cheaper than the fish.

This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it, and the time to find one is before you need one.

Bedding and substrate

3 safe, 4 with a caveat, 2 to avoid

Substrate in an aquarium is a filter as much as a floor. Most of the biology lives in and on it.

Safe

Fine, smooth sandCorrect for corydoras, kuhli loaches, eartheaters such as rams and acaras, and anything else that sifts or burrows. Barbels wear away on sharp gravel.

safe

Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras)Rinse thoroughly before use. Grain size should be too large to swallow and too small to trap food. Kuhli loaches need sand to burrow into and rams and acaras sift mouthfuls of it; bronze and panda corydoras manage on smooth fine gravel, but sterbai corydoras need sand.

safe

Bare bottom (quarantine and grow-out only)Legitimate for quarantine and grow-out tanks. Easy to clean, but it holds far less biological filtration, and it is no long-term home for burrowing loaches or sand-sifters.

safe

With a caveat

Crushed coral or aragoniteDeliberately raises hardness and pH. Correct for rift-lake cichlids, wrong for soft-water species.

with a caveat

Aquasoil for planted tanksExcellent for plants, but most active soils soften the water and pull pH and KH down for months, and many leach ammonia for the first weeks. Right for soft-water species; wrong for hard-water animals (livebearers, rainbowfish, goldfish, and snails, whose shells erode in soft, acidic water) unless you test GH and KH and remineralise. Cycle around it; do not stock into it.

with a caveat

Very deep sand bedsAnaerobic pockets form below about 2 inches in still sand. Either keep it shallow or keep it stirred.

with a caveat

Painted or coated gravelUsually fine, but coatings chip. Test a handful in a jar for a week first.

with a caveat

Never

Sharp or angular gravel with bottom-dwellersWears down barbels and leads to infection in corydoras and loaches.

never

Anything containing metal, limestone of unknown origin, or shells in a soft-water tankSlowly alters chemistry in ways that are hard to diagnose later.

never

This is our general list for freshwater fish. We have not built one specific to Catfish yet.

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