Substrate

What is the best substrate and why?

Substrate for Corydoradinae catfishes has be the topic of many many discussions over the years, and the more and more hobbyists that go to South America to catche their own fish very quickly discover that the bottoms of the rivers and streams are not all covered in a layer of rough gravel. Yes there are many rocky places where some of our favourite fishes are found at certain times of the year, but in the main their habitat consists of a soft substrate, which allows them to sift through and filterout food particles. The substrate may be sand, mud, silt, or combinations of all three, and quite often there will also be a lot of natural debris in the form of leaf litter and fallen branches and trees. 

Anyone that has sat and watched their Corys feed over sand, will see them take up mouthfulls and appear to roll it arround in the mouths and eject the unwanted non edible material ought through the base of the gills.

Corydoras ornatus feeding.

Different groups within the family Corydoradinae feed at different areas of the substrate. As shown in the link above, the long snouted  species, both straight and saddle shaped will if needed, go deep into the substrate to find there desired food, the shorter sounded snouted species such as CW051 will only penetrate a few milimeters and the smaller dwarf species like C. ortegai  generally just mouth the surface.

Corydoras sp. CW051 Feeding

Corydoras ortegai Feeding

 So when you realise what these litte fishes are doing and the material that they are taking into their mouths, rolling it arround and then ejecting it, you will understand why a lot of emphasis is put on what the texture of the substrate should be. My term for the ideal substrate is "A fine, smooth grained sand" as long as the particles/grains are rounded like pebbles then there should never be any problems with damages mouths.