Let's Talk Substrate for a Moment

[TwoTankAmin]

Years back I bookmarked a video on Aquanet TV which is usually in German. However, the vid I bookmarked was titled "Soft barbels on sharp gravel. Surprise, Corydoras live on various substrates." I posted the link to this vid on a few sites, maybe even here. But then that vid disappeared.

I got curious about it again today and headed to the Aquanet TV site. It was all in German which I do not speak. But i decided to go through all their vids and see if the still pic and the title gave me any clues. To my surprise almost at the end of the list I discovered one entitled "Corydoras auf scharfem Kies im natürlichen Biotop" and had a promising looking still. So I ran the German title though Google Translate and this came up, "Corydoras on sharp gravel in the natural biotope."

So here is the vid. It too is all in German, but I did recognize the names of the corys they shot.

 

[Rusty_Shackleford]

I ran across one the other day showing Corydoras on gravel in the Rio Paraguay. I'll try and find it again.

 

[WhistlingBadger]

I believe that a lot of our beloved fish are more adaptable than most people give them credit for. I do not have the gift of cories; mine almost always end up with eroded barbels, even though I keep them on play sand and regularly clean mulm off the bottom. In a previous tank I had a group of panda cories on black blasting sand (very sharp, microscopically) for several years and they were just as healthy, active, and long-barbelled as could be.

I suspect a lot gets blamed on sharp substrate that is actually from other causes.

 

[jaylach]

I would not ha issue with having corries with a gravel substrate but the substrate would be polished river pebbles that would not have sharp edges.

 

[AJ356]

Isn't part of the argument about the "sifting" as well? The same argument that is made for fish like Geophagus cichlids? Or even Firemouth's? I guess that doesn't change the point of the thread, be it sifting or barbell damage.

Perhaps.......... we see a fish exhibit a behaviour in a certain environment (like sand) and assume that the said fish "enjoys" doing the behaviour, and therefore, if the sand (or whatever it is) is not available for the fish, the said fish is said to have a "reduced quality of life" or similar?

I realise "sifting" is about food in-take more than pleasure for the fish?

I guess it all comes back to us trying to differentiate between what is our assumptions about what is "best" for a fish, and what is backed up by nature and/or science.

I was going to say backed up by our own "experience" as fish keepers, but I guess our "experience" can also be shaped by our own bias, or what we "want" to see or "want" to find.

 

[GaryE]

It's about physiology. The structure of the gills is adapted for sifting.

A lot of videos are shot where you can get into the water. And that's around bridges in many cases, as deeper in the vegetation, it's hard to get access. Bridge construction and road construction disturb environments, and very often add gravel. And boulders. You sometimes see rivers with no boulders til you reach a bridge, and everything changes.
As well, the Corydoras group move and migrate through all sorts of habitats.

My Cory group fish have never had barbel loss, in 59 years of keeping them. I use pool gravel mixed with sand. It isn't ideally sized for sifting, but it works.

With Geophagus, Apistogramma and the old Cory group, you can't get around the anatomy. It's their favoured manner of eating.

 

[fishorama]

My corys over the years have never had a problem feeding on small gravel or coarse pool filter sand.

As for "natural behavior", can we really compare pellet, other manmade foods or even live foods to what they'd have to work harder to find in nature? In my experience with corys & cichlids they may spew fine sand or foods from their gills; if too coarse; they just spit it out. For live worms corys, larger cichlids & loaches often went head first with just their tails sticking up. Never an injury but some happy wiggling & chewing, lol.

There was an amateur study of 2 groups of corys 20+ years ago. 1 was kept on glass shards but low nitrate level. The other was on fine sand but high nitrate. Surprise! The glass substrate corys had no barbel wear or erosion but the sand & high nitrate fish did., often quite severe. He didn't keep it going for more than a couple months AFAIR. The original link is archived & no longer supported nor is a different board's link to it.

 

[GaryE]

Aquarists 80 years ago decided Corys were a clean up crew. It was cute. It was what we wanted to hear. Fish to clean the tank seemed very convenient.
Reality is they are fish with a strong sensitivity to pollution and decay, and they need to be cleaned up for. They need clean tanks and clean substrates, and aren't fish for lazy aquarists.
I like to see them sifting sand. It's close to natural behaviour in a tank, although as @fishorama noted, they aren't hunting in most tanks. We have a shortage of invertebrate larvae and worms in our home aquariums, and that's what they dig for. We can give them insect based food (For the past 3 weeks I've given a frozen paste I make with soldier fly larvae, and use two types of insect based tiny pellets, as well as white worms. Yes, I feed Corydoras group fish directly, and not with that the other fish miss) but we lose behaviour, for what that's worth to us.

Substrate? We can look at diagrams of their mouth and throat/gill structures. We know they sift and filter. We know they're from the Amazon region which is low mineral (in general) with well worn rocks of all sizes. They live on the bottom (in general). So sharp substrates are out, just on a common sense or common kindness basis.

We have learned how sensitive they are, and that one response to filth is barbel erosion. So substrates that trap and hold food and waste aren't sensible for them. If they move over gravel in nature, so do millions of gallons of flowing freshwater, scouring the substrate. In a fishtank, food drops down and is trapped. Pebbles are terrible for this, so pebbles are a poor idea for Corys.

I'm sure barbels can get cut. They are delicate. We know ammonia can burn fish. We're always looking for either/or in Cory tank debates, but I'm sure we're dealing with combinations in most tanks. I have seen one thing of value to the discussion though - healthy looking Corys arriving in bare, poorly maintained store tanks and suffering barbel erosions when they didn't sell quickly. There were no sharp edges. The store owners didn't even have sharp edges in the brains, from what I could figure out...