Why Corydoras Are the Community Tank's Best Friend
Corydoras catfish are small armoured catfish from South America in the family Callichthyidae, comprising over 170 described species. They inhabit shallow, clear to murky rivers, streams, and flooded areas throughout tropical South America, where they live in large schools foraging along the substrate. Their adaptability, peaceful temperament, small adult size (2-8 cm depending on species), and natural bottom-feeding behaviour make them one of the most useful and entertaining community tank inhabitants available. In Cambodia, common Corydoras species are available in virtually every aquarium shop.
The community tank role of Corydoras is often oversimplified as "tank cleaners" — while they do consume uneaten food and organic debris from the substrate, they are far more than living vacuum cleaners. They are active, social fish with distinct personalities that explore every corner of the tank with their sensitive barbels, chase each other playfully, and engage in synchronised schooling behaviour when kept in adequate numbers. A school of 8-10 Corydoras in a planted tank creates constant interesting movement at the bottom level that complements the mid-water and upper fish.
For Cambodia-based hobbyists, Corydoras represent excellent value and wide availability. Common species like C. paleatus (Peppered Cory), C. aeneus (Bronze Cory), C. trilineatus (Three-Line Cory), and C. panda (Panda Cory) are regularly available at Phnom Penh aquarium shops for 3,000-8,000 KHR per fish. Premium species like C. sterbai (Sterbai Cory), C. adolfoi, and Venezuelan black Corydoras are imported periodically from Thailand and Malaysia at higher prices but are worth seeking for their exceptional colour patterns and hardiness.
- ✦Buy all Corydoras of the same species at the same time if possible — different species of similar size will school together loosely, but same-species schools are far more active and entertaining
- ✦Corydoras from the same species batch at the same shop are likely siblings — they school most tightly with fish they have known from juveniles
- ✦C. sterbai tolerates temperatures up to 30°C — the only Corydoras species fully compatible with discus tanks in Cambodia's warm climate
Schooling Minimum — Six Fish Is the Absolute Floor
Corydoras are obligate schooling fish and suffer genuine psychological and physical stress when kept in insufficient numbers. A single Corydoras or a pair will spend most of their time hiding, barely move around the tank, lose colour, and show reduced feeding enthusiasm. At 4 fish, a partial schooling response appears but the fish are still clearly uncomfortable. At 6 fish, genuine schooling behaviour emerges — the fish move synchronously, explore openly, and display the full range of natural behaviours that make them interesting. Minimum 6 is not a guideline; it is the welfare minimum.
The optimal group size for most Corydoras species in a 100-200 litre community tank is 8-12 fish. In this range, the school is large enough to have internal social dynamics — dominant foragers, following fish, individuals that explore independently and return to the group. Observing this natural social behaviour is genuinely engaging and educational. In Cambodia, buying 8-10 Corydoras in a single purchase from a single tank at one supplier is the recommended approach — all fish from the same colony will have the same disease history and adapt to your water parameters together.
Different species of Corydoras should not be mixed in small numbers — a group of 3 C. aeneus and 3 C. paleatus totalling 6 fish does not provide the schooling benefit that 6 of the same species does. If you want to mix species, buy 6+ of each. Many Phnom Penh aquarium shops sell Corydoras in assorted groups — these are fine for community colour variety but for optimal welfare, same-species groups of adequate size are always superior. The price difference between assorted and same-species groups is usually minimal.
- ✦Never buy fewer than 6 Corydoras of the same species — 4 fish will huddle in a corner and 2 fish will slowly decline in health
- ✦If your budget allows only 4-5 fish, wait and save — buying the correct number once is better than buying wrong twice
- ✦C. aeneus and C. paleatus are the most affordable and commonly available in Cambodia — start with 8 of either species before exploring premium varieties
Sand Substrate — the Critical Corydoras Hardware Requirement
The most important hardware decision for Corydoras is substrate choice. Corydoras have sensitive barbels (whisker-like sensory organs) that they use to probe the substrate for food particles. On coarse gravel substrate, these delicate barbels suffer repeated minor abrasions that accumulate into bacterial infections — a condition called "barbel rot" that shortens barbels, causes chronic pain, reduces feeding ability, and shortens the fish's lifespan significantly. The solution is simple and inexpensive: fine silica sand or smooth fine gravel of particle size under 1mm.
Fine silica sand is the optimal substrate for Corydoras and is available at aquarium shops in Phnom Penh and at hardware stores (sold as filter sand or play sand) throughout Cambodia. A 3-4 cm deep layer of clean fine sand in a 100-litre tank costs under $5 USD and transforms Corydoras behaviour dramatically compared to gravel. Corydoras on appropriate sand substrate will be observed sifting continuously, plowing their snouts through the sand, and occasionally burying themselves partially — natural behaviours they cannot express on hard or coarse substrate.
Washing sand before use in an aquarium is essential. New sand contains fine dust particles that cloud the water for days if added unwashed. Rinse in a bucket under running water, stirring and decanting the cloudy water until the rinse water runs clear — typically 4-6 changes are needed. Spread washed sand thinly in the tank first, add a few centimetres of tank water, and check clarity before filling fully. In Cambodia's dry season, sand rinse water can be conserved and used for garden irrigation — a small environmental consideration that reduces water waste.
- ✦Grade 0.3-0.8mm silica sand from building supply shops costs 5,000-10,000 KHR per 5kg bag — far cheaper than aquarium-branded sand with identical properties
- ✦Avoid pure white sand for Corydoras display tanks — off-white or slightly tan sand better mimics their natural riverbed and reduces stress from excessive light reflection
- ✦Check barbel length monthly — shortening barbels are an early warning of substrate abrasion damage, water quality issues, or bacterial infection
Temperature, Water Parameters, and Species Compatibility
Most Corydoras species prefer water temperatures of 22-26°C — slightly cooler than the 26-28°C standard for many tropical community fish. This cooler preference is an important compatibility consideration. Corydoras are generally fine at 26-27°C, which is the standard range for tetras, guppies, and angelfish — the most common community tank species. At 28-30°C (discus temperature), most Corydoras species show stress. The exception is C. sterbai, which naturally inhabits warm tributaries and tolerates up to 30°C, making it the only Corydoras fully compatible with discus tanks.
Water chemistry tolerance in Corydoras is moderate — they adapt to a wide pH range (6.0-7.8) and moderate hardness (GH 4-15), making them compatible with most community tank water conditions without special adjustment. They produce relatively little waste for their size and do not significantly change tank chemistry. Water change frequency should follow the main community tank schedule rather than being altered for Corydoras specifically. A 25-30% weekly water change in a well-stocked community tank with Corydoras maintains excellent water quality with minimal effort.
Corydoras compatibility with other fish is excellent across virtually the entire range of peaceful community species. They coexist peacefully with tetras, rasboras, guppies, mollies, angelfish, gouramis, small loaches, and peaceful barbs. The only fish that present a danger to Corydoras are large aggressive cichlids (Oscars, Flowerhorns), large predatory fish, and large aggressive loaches that compete for the same bottom territory. Corydoras should never be kept with goldfish (too cold and waste-producing) or with bettas in very small tanks (bettas may nip Corydoras fins in confined spaces).
- ✦C. sterbai is worth the premium price ($3-5 USD vs $1-2 for common species) if you want Corydoras compatible with a 28°C discus or angelfish tank
- ✦Do not use Corydoras as the solution to excess uneaten food — they are supplementary scavengers, not a substitute for proper feeding discipline
- ✦Corydoras breathe atmospheric air by surfacing periodically — a normal behaviour that alarms new keepers but is completely healthy in Corydoras
Popular Species Guide — From Common to Rare
Corydoras aeneus (Bronze Cory) is the most commonly available species in Cambodia and one of the hardiest — an ideal starter species. They reach 6-7 cm, tolerate a wide range of water conditions, and breed readily in home aquariums. C. paleatus (Peppered Cory) is similarly available, slightly smaller at 5-6 cm, and distinguished by its marbled black-and-grey pattern. Both species are excellent choices for beginners and are available year-round at most Phnom Penh aquarium shops at very affordable prices.
Corydoras sterbai is one of the most sought-after species in the hobby — its distinctive spotted pattern and warm-water tolerance (up to 30°C) make it the premier choice for discus and high-temperature community tanks. C. panda (Panda Cory) is a striking small species (4-5 cm) with black eye patches against a pale body — popular for nano tanks and smaller community setups. C. adolfoi and C. duplicareus are rare imported species with extraordinary orange-red colour on the head that commands premium prices from collectors. All these species share identical basic care requirements.
Breeding Corydoras is accessible and rewarding for intermediate hobbyists. Most species follow the same spawning pattern: the female "T-positions" against the male, receives sperm, holds the fertilised eggs against her body, then deposits 2-4 eggs on a cleaned surface (usually glass or broad leaves). The spawn produces 100-200 eggs over an hour. Eggs hatch in 3-5 days at 24-26°C. Fry accept BBS and micro-pellets within days of becoming free-swimming. In Cambodia, locally bred Corydoras are highly valued and a productive pair of C. sterbai or C. adolfoi represents meaningful income from a modest breeding setup.
- ✦Trigger Corydoras spawning with a 2-3°C temperature drop (simulating rain season flood) combined with a large water change — many hobbyists in Cambodia use the seasonal temperature drop naturally
- ✦Move Corydoras eggs to a separate hatching container with a drop of methylene blue to prevent fungal infection — survival rate increases from 40% to 80%+
- ✦Rare imported species like C. adolfoi and C. weitzmani are occasionally available from Thai importers through Cambodia aquarium networks — join Facebook groups for availability alerts