Sorting through the catappa leaves...searching for the facts beneath the jargon.

So, pretty much everywhere I go, people who are unfamiliar with our geeky little botanical world and it’s tricks and crazy ideas are generally asking me why Catappa leaves seem to have some sort of “lock” on the collective consciousness of people who swear by them. Is it some weird, cult-led devotion? Some crazy anecdotal ideas that ended up getting twisted and warped into some yarn that they contain magical powers?


Well, if you read some blogs and articles in the some corners of the aquarium world, you’d be inclined to think this! There is a lot of wordy gobbledygook out there that sounds very impressive...but what does it all mean for us as fish geeks?

And of course, if you read my blog, I spend an equal amount of time erasing biofilms and decomposition, so... yeah. I may not be the guy to sort it all out...but what the hell...I'll give it a little shot here.

Back to Catappa...

There’s a lot of claims attributed to these leaves, and it’s often hard to sort through all of the hyperbole and find the potentially true facts that might be of interest and value to us as aquarists. The last thing I want to do is get caught up in touting all sorts of unsubstantiated claims about these leaves and the substances they contain, so I did my best to ferret out just what the ”real deal" is here!

And it isn't all that clear.

I mean, we have featured a lot of information about the benefits of humic substances, which catappa and other botanicals are known to impart into the water, and those are significant. However, when the hobby praises catappa, specifically, I wonder exactly what these leaves are purported to do...and how/why they supposedly do it.

As you know, I'm no chemist, but I do know how to look stuff up (which often leads me down the "rabbit hole" to some sort of trouble, lol), coffee in hand, I jumped in a little bit deeper into the whole lore of Catappa benefits, and give a little summary of some of the most commonly touted "beneficial compounds" (in hobby articles) which are contained in them, and what they might do for fishes, based on the scientific research I could find. Now, again, I'm no scientist as you know, and some of the terminology we’ll use still sounds a bit “fancy”- perhaps even vague, but I tried my best to “translate” some of the really “hardcore” scientific jargon into some stuff that is decipherable to us mortals!  

And I can't help but wonder...

I mean, some of the compounds in catappa are known to have benefits in humans. However, I am curious how some of these things really "translate" over to fishes, you know?

The practice of using catappa leaves in aquariums is quite old. And there is a certain logic to their use, which is hard to question. For many years, Betta breeders and other enthusiasts in Southeast Asia added catappa leaves to the tanks and containers that held their fishes, and noticed a lot of positives…Those who actually fought their fishes seemed to feel that, when kept in water into which catappa had been steeped, their fishes recovered more quickly from their injuries. Those who simply kept fishes (not for “blood sport”) noticed increased overall vigor, appetite, and health among their fishes. 


Anecdotal? Perhaps.I mean, probably...

However, one thing I've learned about the early aquarists is that they employed very keen power of observation. They were a practical lot, if nothing more, who didn't have the internet and cool gadgets and stuff to rely on for information. It was more about trying stuff and going with things that seemed to work for them. They were obviously seeing something- or a combination of things, which led them to believe that using catappa leaves  was beneficial to their fishes.

Now, this makes a lot of sense, right? I mean, the natural habitats of many of the fishes of Southeast Asia are blackwater, botanical-influenced waters, rich with tannin from decomposing vegetation and naturally occurring peat. We’ve talked a lot about the benefits of “humic substances” for fish health, and, not surprisingly, there has actually been a fair amount of scholarly research into this area, mainly in the area of food fish production…and much of it points to the fact that many of the humic substances and compounds which benefit fishes are found in…surprise! Catappa!

So, if the men and women in the white coats feel that there is something there, we should take notice, huh?

Well, we should check it out!

The bark and particularly, the leaves of the Indian Almond tree- contain a host of interesting chemicals that may provide direct health benefits for tropical fishes. The leaves themselves contain several flavonoids, like kaempferol and quercetin, a number of tannins, like punicalin and punicalagin, as well as a suite of saponins and phytosterols. Extracts of T. catappa have shown some effectiveness against some bacteria, specifically, Plasmodium, and some parasites as well. 


As we all know by now, when catappa leaves are immersed in water, the tannins and humic substances are released, which can lower the pH of the water if their is minimal general hardness. The tannins are what tint the water to a beautiful brownish color which we devotedly call “blackwater.”

But, you kind of knew that already, huh?

It has even been postulated by some that the tannins in Catappa leaves are able to reduce the toxicity of heavy metals in aquarium water, essentially binding them up or chelating them- if true, a most interesting benefit for the urban fish keeper, I might add! I think that’s a pretty big supposition, but I suppose it’s possible that it can be true, right? I mean, it's not by "magic" if this happens...there is probably some chemical process which occurs to make this happen..

At this point, you’re probably thinking, ”Okay, Scott. All of that stuff sounds very scholarly, but what exactly are those things that are in catappa, and what can they do for my fishes?”

There are really a few that I found which have alleged benefits for humans- and for fishes...So I'm just focusing on them in the context of this piece, okay?

Well, lets start with the flavonoids. Flavonoids have been shown by science to have direct and synergistic antibacterial activity (with antibiotics) and the ability to suppress bacterial virulence factors in a number of research studies. They may also act as chemical "messengers", physiological regulators, and "cell cycle inhibitors", which bodes well for their use as a prophylactic of sorts. Kaempferol, a noted flavonoid,  is thought to have anti-inflammatory and antioxidant properties. Could this be why Betta fanciers used them for so many years after fighting their fishes?

Perhaps, right? Tradition!

Saponins can be used to enhance penetration of macromolecules, like proteins, into cell membranes. Some are used in vaccines to help stimulate immune responses, so you can imagine some potential benefits here as well, right? Yeah!

Yeah, I can see that.

Phytosterols are interesting for their alleged capacity to reduce cholesterol in humans, but the benefits are probably non-existent, or minimal for fishes, especially as it pertains to Catappa leaves in the aquarium! I mention them in this piece merely because fishy marketers touting the benefits of Catappa leaves love to throw them out there for reasons I cannot grasp- or maybe just because they are in catappa and it sounds cool? Dunno.

IMHO, it's pure marketing B.S....I mean, it sounds cool and all, but... Yeah.

Punicalagins act as antioxidants and are the major component responsible for the antioxidant health benefits of fruits, such as pomegranates (The really messy fruit that I always hated as a kid...). They are water soluble and have high bioavailability, so it is quite possible that they are of some benefit to fishes! I mean, antioxidants , right?

There must be a study out there on the benefits of antioxidants for fish health, right? That's worth a gander on Google, huh?

I did find a cool study conducted by fisheries researchers in Thailand on Tilapia, which concluded that Catappa extract was useful at eradicating the nasty exoparasite, Trichodina, and the growth of a couple of strains of Aeromonas hydrophila was also inhibited by dosing Catappa leaf extract! In addition, this solution was shown to reduce the fungal infection in Tilapia eggs. 

That's pretty significant, and correlates nicely with some of the much-touted anti-fungal properties of catappa leaves. Perhaps this is the most interesting and logical of the many claims made about catappa leaves and their capabilities at enhancing fish health!

For reference, here is the study:

(Chitmanat, C., Tongdonmuan, K., Khanom, P., Pachontis, P. and Nunsong, W. (2005). Antiparasitic, Antibacterial, and Antifungal activities Derived from a Terminalia catappa solution against some Tilapia (Oreochromis niloticus) Pathogens. Acta Hortic. 678, 179-182

DOI: 10.17660/ActaHortic.2005.678.25)

Now, that's as far as I could handle going before my head was ready to explode!

And I think I covered some of the major compounds found in catappa as they pertain to fish health benefits, as touted by aquarium hobby marketers and authors. Are there others? Of course there probably are...and probably an equal number of anecdotal claims of stuff they do.

But I"m done for now, lol. I'm reasonably satisfied with what I've uncovered.

Suffice it to say, my very superficial examination of this stuff has, as usual- raised as many questions as it answers (did I answer any, actually?). That being said, I think it might be safe to say that, despite some of the marketing BS that's been circulating around the use of catappa leaves in aquariums, there may very well be some "legit" science and real tangible benefits for fishes from their use.

I mean, we are inundated daily with reports of how nice and healthy customers' fishes are looking when catalpa and other botanicals are used in their aquariums, and how such-and-such a fish that never spawned before laid eggs a week after the botanicals were introduced, etc...


I don't think so. However, before I personally start advising everyone to toss leaves into their spawning tanks as an antifungal, I'd love to see even more and more practical research on the hobby level. You know, comparing egg viability in killies or tetras or Apsitos, for example, in systems with and without the blackwater conditions.

As I've said so many times before...the blackwater aquarium world has so many more secrets and discoveries to be revealed- so much to learn...and so much to be done as we literally pull the practice of botanical-style blackwater aquariums out from the shadows of the hobby. With the potential for legitimate breakthroughs just hanging out's up to us to get to the bottom of it all!

Who's in?

Stay bold. Stay Experimental. Stay fascinated. Stay skeptical. Stay open-minded...

And always...

Stay Wet.


Scott Fellman

Tannin Aquatics 


Scott Fellman
Scott Fellman


1 Response

David Flynn
David Flynn

December 20, 2017

A very interesting and thought provoking article.

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