What really makes those catappa leaves tick?

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-lied 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’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! None of this is the definitive word on the subject, but it was helpful for me to at least try to extract some practical information out of the many claims about these leaves.

I figured I’d delve just a little bit deeper into the whole lore of Catappa benefits, and give a little summary of some of the beneficial compounds which are contained in them, and what they might do for fishes, based on the scientific research I could find. Now, 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!  

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. 

 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!


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 Indian Almond 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 visually tint the water to that beautiful brownish color which we devotedly call “blackwater.”


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


 Just what DOES make these leaves tick?

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?


Catappa leaves also contain substances known as  Saponins, which 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. possibly?

Phytosterols are interesting for their alleged capacity to reduce cholesterol in humans, but the benefits are probably non-existent for fishes, especially as it pertains to Catappa leaves in the aquarium! I mention them in this piece merely because fishy authors touting the benefits of Catappa leaves love to throw them out there for reasons I cannot grasp! Maybe it just sounds good. Don't know...

Punicalagins act as antioxidants and are the major component responsible for the antioxidant health benefits of fruits, such as pomegranates (You know, the "wonderful," yet 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 found 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.  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)

So, sure, like so many other aquarium-related matters, there are some possible "side stories" to use of Catappa leaves in our tanks. And benefits that are known and perhaps not yet studied. We do know that there are some well-studied positives that can be achieved by using them in the aquarium. Much is still anecdotal for aquarium use- a "forced fit" based on the known benefits of these compounds for human health...And much remains to be discovered about their benefits for aquatic use.

I think that the use of Catappa leaves in the aquarium will continue to be a practice that we should study. And, regardless of how you choose to employ Catappa leaves and other botanicals in your quest for a "blackwater" aquarium, it's important to take a cautious, responsible, well-informed approach. We'll keep doing our best to disseminate as much information as we can about the materials we offer. Knowledge is a key to success and stability in all areas of the aquarium hobby, and you should arm yourself with as much information as possible, for the benefit of all of the fishes under your care. 

Stay curious. Stay open-minded. Stay skeptical. Stay engaged.

And Stay Wet.


Scott Fellman

Tannin Aquatics 



Scott Fellman
Scott Fellman


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