Do Corydoras Filter Feed?

  • #1
I am wondering what the members of this forum think.
Do Corydoras filter feed? Is it vital for Corydoras to live only on sand? Can Corydoras be kept on a fine gravel substrate successfully?
Just a couple of questions that I'm curious about.

  • #2
Ive kept them on gravel successfully and they seemed to be fine with. I will say when i switched to sand they seemed to enjoy sifiting more and it definitely seemed more natural for them. I wouldn't say it's vital but it's recommended imo.

  • #3
I've seen reports that people have seen them in the wild on smooth gravel.
  • #4
They can be kept on most any substrate. Many people do not keep them on sand. Supposedly their barbels are eroded by rough substrate, but there is no proof. Corys living on sand can lose their barbels. Corys living on sharp, rough substrate can have big healthy barbels.

Sand is probably more like their natural habitat and so may be more likely to illicit natural behaviors.

They are not filter feeders. They sense food with their barbels and then eat it. Sometimes that means sticking their head into the sand to find a morsel.
  • #5
They should be fine on most substrate from what I've read about them, I have one on regular pet store gravel and it does fine, I've heard they also do fine in sand. They feed mostly on leftover food that falls to the substrate and mine actually likes to eat the algae wafers I put in my tank for my pleco.
  • #6
The barbel erosion is a myth although if the substrate is uncomfortable you'll know it because they will keep away from it.

The infections and erosion or rot of barbells and skin is from poor substrate conditions. Fish should always be able to heal wounds injuries and regrow skin and fins given the right conditions and they are healthy. and stuff like barbell erosion doesn't happen, they get an abrasion, it doesn't get infected and heals and they move on.

People have a tendency to think bottom feeders eat "waste".. they don't eat poop and shouldn't live in it either.
For whatever the reasoning, people think catfish live in and eat poop and it's OK to keep a dirty tank bottom. It's just not.


86 ssinit
  • #7
Wow I’ve heard so many times about them not being good with gravel. Been insulted for keeping them on gravel. I’ve never had a problem with them on gravel. Though stuff like eco-compleat should be avoided! Well it should be avoided compleatly :eek: :eek:.
  • #8
  • #9
I have cory cats in 3 tanks - all gravel, pretty nicely rounded gravel though

20 long ( green cats) , 20 tall (5 false julii) and 38 gallon tank ( green cats)

no issues the last 4+ years
I even gave away 12 emerald cory cats about 18 months ago because mine were breeding like crazy!
  • Thread Starter
  • #10
No. Baleen whales are filterfeeders. Whale sharks. Manta rays. Flamingos. But also their food like krill, mysis, artemia. Even herring are filter feeders.
I basically got banned from another forum site because I insisted that they weren't filter feeders. I also pointed out that they could live on gravel which I was told that I was cruel and the Corydoras couldn't filter feed on gravel so they would starve to death.
I am pleased that the members of this forum site are a little more rational about this subject than those on the site I was banned from :) ;)


  • #11
I simply don't see the connection of filterfeeding and substrate as filterfeeding means filtering food from the open water and not from chewing the substrate.

Chewing substrate is called sandsifting and in freshwater that's most common in cichlids (Geophagini in South America, includes Mikrogeophagus and Apistogramma. Lethrinops of Lake Malawi and sand cichlids like Xenotilapia of Lake Tanganyika.), but also Catfish, including Corydoras.
Of course all these fish can feed without sand. I find it's most appropriate to keep them on a sand substrate, though, as this rules out many common problems by default.

The human factor is the bigger problem. Laziness in maintenance, bad planning of a setup, insufficient research, carelessness or outright negligence of (self-)education and most disturbing: Ignorance of priorities.
Many don't even know why the things they do work or not. And thus many make assumptions that are hilariously off the actual reasons.

And yes, I don't see a point discussing the "sand or no sand"-question. I'm making this a question of basic principle:
If a species has a certain lifestyle and habitat in nature is it acceptable to ignore that when laying out the concept of a tank for/including this species?
(It's a rhetorical question, but my answer is: No, it's not acceptable.)

Enjoy the thought. Savour it for a bit.

I'm off to work.
  • #12
I think the confusion is just the wording, people see them sifting sand through their gills & think they’re filter feeders which is different.
Corys are sand sifters which is why a sand substrate is preferable for them,
This video - not mine- shows how they take in mouthfuls of sand & sift it through their gills

Many people do keep them successfully on small gravel such as pea gravel as they can still move that about to forage for food, keeping them on a large size gravel causes issues as food drops down out of their reach & decomposes, which can contribute to poor water quality barbel loss.
Barbel loss tends to occur more often when kept on a combination of sharp gravel along with dirty substrate, small nicks & cuts can allow bacteria in from foraging in dirty/decomposing material.
In short give them sand wherever possible, have a good maintenance regime & you’ll have happy healthy corys.
  • #13
The main thing with substrate for any catfish is that you do not want to have sharp edges that can damage the mouths of the fish as they root around for food on the bottom. I use coated gravel rather than uncoated. The primary reason is that the coating minimizes dust when you first add gravel to the aquarium. The second reason is that the coating smooths over sharp edges which might be harmful to fish.
  • #14
I see the like minded folk already chimed in on filter/sift lol
  • #15
I've had them in my tanks for years and i have gravel in my tank as I'm sure many others do also never had any problem with them as far as that. Perhaps they do prefer sand over gravel and that would be more natural to them, but i don't think you having gravel will be so detrimental to them that they would have problems in the tank all the time. As others said if it's not sharp pieces of gravel just smoothed gravel i think would be fine.

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