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I am involved in an Aquarium Association, and am looking for subjects for presentations at our meetings. Some members are keen to learn about ‘black-water pleco tanks’.

I am in NZ and black-water tanks are currently all the rage around here. Fancy plecos have been in fashion for ages, and that’s unlikely to change anytime soon. I understand the desire to combine the two.

But I wonder, isn’t the sucker-mouth an adaptation to fast flowing water? Fast flowing water is usually clear and just about the opposite of black-water.

Is black-water pleco an oxymoron or am I missing something?

Hi all,

fmueller wrote: ↑12 Apr 2024, 12:46 But I wonder, isn’t the sucker-mouth an adaptation to fast flowing water? Fast flowing water is usually clear and just about the opposite of black-water.

Maybe not blackwater as such, but I think fast flowing water can be tannin stained, you could have a situation where a "black-water" stream flowed over rock ledges at the edge of the Andes piedmont, Guyana shield etc. The extra oxygen will help with microbial oxidation, but the streams will always have some humic compounds.Even under oxygen rich conditions microbial oxidation will be limited by the lack of other nutrients (fixed nitrogen, phosphate etc.)

Any stream that flows through forest (which in the Amazon region would have been nearly all of them) will pick up humic substances (tannins etc) from dead leaves and fallen wood. I've not kept them, but if they are available to you in NZ? I'm going to suggest or similar.

Anecdotally I raised some in a planted tank with tannins and they did really well. The only noticeable thing was they they were uniformly coloured "chocolate brown and cream", but I don't know if that was genetic, diet based or water related.

If it is a "white water" stream you won't be able to see the tannins, but they will still be there.

If you think about Panaque and Panaqolus spp. etc, they have developed adaptations for xylophagy, and you can't have wood without trees and you can't have tree without leaves.

cheers Darrel

When I was first setting up my tank for altums which is stained. I was interested in a pleco I could eventually add. I had H. contradens and apparently they come from the same region and some of the rivers where the Altums live. I put in a pair of my adults. I lost one after about a 18 minths and the other one lasted for several more years.

Unfortunately, the tank got hit with wasting disease and I lost most of the fish in it. I ultimately got more altums but now they are on their own.

I had the water in that tank and still do at pH 6.0 and TDS in the 60 -70 ppm range. The Altums I now have were bred in Las Vegas by one of he few people in the country who has been able to breed them. Another person bought them and I took them in trade for partial payment for some of my F1 L173. He has since bred my plecos but I will never manage to breed the Altums. I am not that good, not even close.

Plecos evolved as they did because the water where they live is fast flowing. I assume there was a time they dod not live in fast flowing water, But as the flow began to increase evolution took hold. I do not believe they need fast flowing. What I do believe they need is well oxygenated water. I have kept a few plecos over the years and most have spawned in my tanks. But, I also have plecos live and breed in tanks which have only air powered filters and nothing to produce strong flow. I have mattenfilters in some tanks.

I have kept mostly plecos from the Big Bend of the Xingu which has pretty warm water which means it needs lots of churning for there to be adequate DO for the plecos etc. My plecos have done fine in warm water that was well oxygenated and which had good circulation, but nothing that I would call high flow.

I figure the fish have to work harder to function in high flow. So it must be nice not to have to work so hard just to get by.

I've personally never ran into issues keeping plecos in blackwater, and honestly prefer it because it gives me an excuse to not spend a bunch of money on plants and lighting; plus, the plecos- especially fry- seem to love munching on old botanicals. I've actually had the best success breeding certain plecos- L183 being a prime example of this- in blackwater setups, some with dwarf cichlids like Dicrossus and Taeniacara (though in hindsight the plecos occasionally aggravated them by blundering into cichlid-occupied spaces and likely eating eggs and non-motile fry).

I agree with what's been said; most rivers that plecos hail from are still tinted with tannins, and flow doesn't seem to be a critical factor in keeping plecos happy enough to breed and live long-term. Even supposedly rheophilic species like Baryancistrus don't seem to mind hanging out in less-turbid areas of my tanks IME.
+1 on the dissolved oxygen being a critical factor in keeping some plecos; difficult to achieve without fairly heavy flow/surface agitation, meaning certain species will be unsuited for a blackwater setup.

Some of my favourite tanks were ~20-75G tanks with decently heavily tinted water, some large botanicals, and an oversized circulation pump blasting water at a ~50x hourly turnover rate. Was super fun to watch Pseudolithoxus and Pseudancistrus spp. clinging about and foraging on rocks being subject to heavy currents. Certainly not really a blackwater setup in a conventional sense, but not altogether dissimilar, I guess.

On a side note, aren't there dozens of loricariids native to the Rio Negro and its surrounding tributaries, much of which is acidic blackwater?

"But I wonder, isn’t the sucker-mouth an adaptation to fast flowing water? Fast flowing water is usually clear and just about the opposite of black-water."

The "sucker-mouth" may have come about as an adaptation to fast flowing water as it did in Astroblepidae. However, over millions of years loricariids colonized nearly every aquatic environment in South America. The form of the mouth, and possibly even more importantly the teeth and jaw, led to massive diversification. Their less successful cousins the astroblepids meanwhile remained restricted to cool, fast flowing streams.

Constant evolution of the mouth, jaw, and teeth (and the ability to breath atmospheric O2) opened the world to loricariids making them the largest family of catfishes in the world.

So yes, there are 100s of spp of blackwater loricariids. They are just using that "suck-mouth" (and teeth and jaws) for things other than holding onto rocks in fast flowing streams. They are using it to sift sand, catch snails, feed on plants, feed on sponges, eat insects, eat wood, etc.

It is not true that most loricariids come from tannin stained water. The vast majority of South American river systems are either white (northern and western tributaries) or clear waters (southern tributaries). Some of the largest genera in the family are only found in white or clear waters. Blackwater (mainly the Negro and upper Orinoco) spp are simply over represented in the hobby because they tend to be more attractive in coloration.

-Shane

Nature has little choice in terms of evolution as far as I am concerned. It is an ideal way to insure species are best adapted to their environment. It also wants to insure that species survive over time. And for a very very long time nature had its way. What changed things was us. Humans have gained the ability to effect nature in ways no prior species has. We have the power to derail ourselves. But that is another topic for another thread.

What opened my eyes was one of the members here whom I used to know and even have been to his home. He bred heck out of the smaller plecos and his tanks mostly ran on several air powered Poret cubefilters. Here his user name was CodOnMyRod. https://www.planetcatfish.com/common/my ... CodOnMyRod

I learned from this. I have used a lot of mattenfilters and cubefilters in my pleco tanks. Great filters but they do not generate strong flow, but they are good for circulation and aeration.

Thanks to everyone for the input! It helps a lot!