Head to head
Corydoras vs Plecostomus
Corydoras and plecos are the two catfish most often bought to tidy up an aquarium, and the comparison matters because they do very different jobs and have very different space needs.
| Corydoras | Plecostomus | |
|---|---|---|
| Adult size | ~2 to 7 cm | ~30 to 50 cm (common species) |
| Social life | Shoals of 6 or more | Largely solitary |
| Activity | Active forager, day and night | Mostly nocturnal |
| Main food | Sunken food, small invertebrates | Algae, biofilm, wood fibre, vegetables |
| Breathing aid | Gulps air through the gut | Gulps air at the surface |
| Fin spines | Mildly venomous locking spines | Stout, non-venomous spines |
| Waste produced | Modest for its size | Large in a grown adult |
| Best tank | Most community aquariums | A large tank, or a bristlenose instead |
Corydoras vs Plecostomus: common questions
Which is the better clean-up fish, corydoras or a pleco?
Neither is a true clean-up crew, but corydoras come closer to being useful without becoming a problem. They forage across the bottom and eat sunken leftovers, helping stop food from rotting, while staying small enough to suit most tanks for their whole lives. A pleco does graze algae as a juvenile, but a grown pleco needs a large share of vegetable food and driftwood, is not living on algae alone, and its size and waste output can overwhelm a small or medium aquarium. If the goal is genuinely reducing mess without a size problem later, a group of corydoras, or a small bristlenose pleco, is the more sustainable choice than a common pleco.
Why do plecos get so much bigger than corydoras?
It comes down to their evolved roles. Corydoras are small prey animals that survive by being numerous, fast-breeding, and quick to hide in a shoal, so there is little advantage to growing large. Common plecos are heavily armoured, largely predator-proof as adults, and specialised to graze slow-growing food like algae, biofilm, and wood over a long lifespan, and a larger body lets them defend a feeding territory and go longer between meals. The aquarium trade sells both as small juveniles, but only the corydoras stays close to that size, which is why plecos so often outgrow their tank while corydoras rarely do.
Can corydoras and plecos live together?
Generally yes, since both are peaceful bottom-dwellers that occupy the same zone of the tank without competing aggressively, and a pleco is not a threat to corydoras. The practical limit is space, in that a tank large enough for an adult pleco, several hundred litres for a common species, comfortably fits a group of corydoras as well, but a small or medium tank set up around corydoras will not have room for a pleco once it grows. Keeping a small species, such as a bristlenose pleco, alongside a shoal of corydoras in a modest tank is a common and workable combination.