Why do some deny the fact that corydoras DO sift through sand with gills?

[MaloK]

I always considered mulm accumulation as a threat where grows the bad things and toxic emanations you don't want in a closed environment.

Bottom feeders living face in crap never gave good results.

Some are able to grow enough plants to overwhelm the problem, But It's not always the case. I vacuum all that is possible and use fine mechanical filtration that help a lot slowing down accumulation.

 

[GaryE]

I find the title of this thread argumentative... I'm not going to dispute that Cory's sift through sand, I get the most interesting patterns in my white sand tank, from the Cory's, funny that I don't witness the same in my black sand tank... but my understanding, is they are not exclusively found in sand, in the wild, but also in mud, and leaf litter, and occasionally in rocky or gravel areas, unless this was witnessed as only a specific species, in those areas, it shows ( at least the wild ) that they also live in other types of substrate... perhaps there is more food in those areas, than in bare sandy areas??? I do have a small shoal of Serbi's in my South American Tetra tank, that has small rounded river gravel in it, and they have grown to maturity... this tank begs to differ, that they "need" to sift sand to thrive...

I don't think anyone is saying they need fine sand to survive. That would go against decades of hobby experience. People are arguing they are better off in a fine substrate, a different debate altogether. That it's a need is a straw man argument.
And argumentative is good. Disagreement moves things along, as long as we listen to each other or if we think each other are talking mulm, ignore each other...
Mud's fine. They can sift that. The debate really is - are they sifters? The answer is yes. @CassCats has given us a good video example.

I know people who have kept Geophagus and Satanoperca over over gravel/pebble substrates. They are among the most famous sifters kept in the hobby, but aquarists with pebble tanks never get to see the coolest show they could. The fish eat differently when they have to. They survive. They can look good and live long as long as the debris caught by the pebbles doesn't kill them.

Oddly no one denies that eartheaters sift earth, but some do deny Corydoras do. Maybe it's because the other sifters are larger, and tend to attract specialized aquarists. They tend to die fast in beginner tanks, because of their size. I kept a lone Cory over pea gravel with no water changes for close to 10 years when I was a teenager into early adulthood. I wish I'd done better by her with what I know now, but she did survive.

 

[raylove]

You may have seen a thread I started last year. I hadn't kept corries for years as I had no sand in my tank, and whilst I had kept them successfully years ago with gravel, current thinking was that sand was necessary to keep them happy.
This year I finally set up a tank but because I like plants I made it one third sand and two thirds gravel. I introduced 10 corries and they almost totally avoided the sand. I did see them root in it a couple of times and each time it seemed to distress them somewhat. They would often root in the gravel on one side of the sand then swim across it before digging in the gravel on the other side.
It's true that the sand was more exposed because there were plants in the gravel parts, however, after about 10 weeks I gave up and removed the sand. They immediately started rooting around in the newly gravelled exposed bits, so that wasn't what was discouraging them from the previously sandy area.
I certainly don't deny that corries will sift sand but mine didn't seem to want to do so, indeed they seemed to dislike the sand
I should add that I do actually like the look of sand so I wasn't looking for an excuse to remove it (though having done so I'm glad I did as maintenance is easier!). Also, there is nothing wrong with the sand - it is soft play sand and I have used the exact same bag in a small loach tank. That has been set up for maybe 10 months now without issues though in all that time I have never once seen any of the loaches digging or sifting in the sand. The whole tank is sand so they don't have the opportunity to avoid it. It would be interesting to see how they would react if they were given the choice as previously they were housed in a gravelled tank where they dug ceaselessly.
My only conclusion is that whilst sandy tanks are obviously fine for corries as so many people have had success with them, I am not convinced that they are essential for their happiness and as mine clearly seemed to indicate a preference for gravel, that is what I've now given them.

 

[MaloK]

Very sweet of you, giving them the choice and complying with what they prefer

 

[GaryE]

I've done the same 'experiment' with areas of pool gravel, and areas of sand. I get a little lazy sometimes when I convert tanks from one type of fish to another, and tend to throw in a layer of sand if I move Corys to a tank. I have a different conclusion.

Food collected in the gravel, and the Corys (Brochis concolor, Hoplisoma melini now and Osteogaster aenea in the past) dug for it. Food that landed on the sand stayed on the sand, and was scooped up quickly. It didn't get into the substrate to oblige them to work for it.

The gravel I use would be considered sand by many though. It's too coarse for sifting through the gills, but it's still relatively fine, smooth and easy for the fish to move. The sand I use has a pretty tiny grain size - one local brand is close to powdery..

The goal is for the fish to:
a) access fine particled food easily;
b) access invertebrates and bacteria in the substrate, easily and without harm from sharp edges (Amazon rock is weathered and worn to an extreme degree);
c) avoid hitting pockets of decomposing matter.

Fish are aware of the latter. Research has shown one of the tasks of a dwarf Cichlid mother guiding her brood is to avoid areas of low oxygen in the substrate, and take them to cleaner spots. Since they share habitat with the Cory family, I suspect they'd share a sensitivity to the same environmental dangers. We'd know more if Corys had broodcare. Wouldn't that be a show?

My fish would sometimes bury their snouts in the sand, but wouldn't go that far with gravel. And the substrate would always be more than an inch deep.

The gravel was better for my plants, and I tended to leave it where I put them. So the area with gravel was more secure . I hadn't even considered this as an experiment until a few minutes ago - it was just a lazy set up. I saw the Corys on the sand more once the lights were out. The sand types are all lighter coloured than the gravel, so the fish show. My melini are very shy and are in a big tank - a six footer. I do my health checks in the evening as they all gather out front in the tank, where the sandy parts are.

I have atropersonatus in the same large tank, and they never acknowledge the melini, and never want to go where it's more gravelly. They live in the sandier sections. Unfortunately, I lost some of them in the quarantine period, and only have a small group of three. I've got to breed them when they grow more.

 

[Magnum Man]

a couple of my sterbai, and the gravel, that they have been in for over a year

 

[fishorama]

Not really on topic but interesting. There was a hobbyist study of cory barbel "wear". He had 2 tanks 1 bare bottom with high nitrate & 1 with glass shards but low nitrate. It was only in the bare tank that corys' barbels were damaged.

I wish I would have saved it, it's lost now in no longer supported archives.

I have some aenea on pool filter sand & it's too coarse for sifting, but food doesn't fall between the particles much. I vacuum the top 1/4inch layer near plant roots & deeper where there are few roots. I tried "play sand" once & didn't keep it for long. It was very dirty out of the bag, it took a lot of rinsing & had a mixture of grain sizes. & even though it wasn't a deep substrate I saw anerobic areas that MTS snails didn't stir up enough. I tried to be careful vacuuming out the pockets. I never saw any of the small loaches on it sift it either.

I also have Eco Complete (not the sand) that I've used for many years. It's a fairly small rounded volcanic "soil", I'd call it small gravel. I kept small loaches on it. The only time they dug was when I fed live blackworms. I freaked out when I saw just a tail sticking up! But he popped right up happily chewing, no barbel damage on Eco either.