Reading the leaves....

The other day, one of our Instagram followers (do YOU follow us on Instagram? We have a pretty devoted following, ya know...) asked me about the benefits of Guava leaves. And I received a few pm's after that from others asking about Catappa leaves...which are pushed all over the internet, with various degrees of "miraculous" capability ascribed to them...ranging from compelling to cringe-worthy, depending upon the source... 

Oh, and regarding source...

NEWS FLASH: We're not the only place you can buy catappa leaves from. Yeah, there are vendors everywhere.

Periodically, some wiseguy will tell me to get off "my high horse" (actual words from one message I received some time ago), and that they can "get 8 more leaves or whatever from the guy on that other site in __________ for less..." and that I should "watch my back..."  Others "inform me" out of concern, which is great. But there is simply no reason to be concerned about this...And of course, my response is always the same: It's a big beautiful world, and you can support whoever you want. If it's really important to get the extra 8 leaves or whatever for a bit less, from the guy who just sells you some cheap leaves online in an envelope, support him.

Maybe that's all you're looking for. That's cool. 

I'd like to think that maybe you'd rather deal with Tannin, because we have developed a brand, a culture, fostered a hobby movement, supports clubs and sponsors their events, organizations like Project Piaba, hobbyists, world-class aquascapers, and have a vibrant international online community, a wide variety of botanical items, customer support at a high level, a daily blog with free, honest and sometimes not pretty information about botanical-style/blackwater aquariums shared all over the internet....yeah... Don't get me started, lol. But the bottom lien is that these leaves were available long before we appeared, and there are lots of places to get them. Some give you more leaves at a lower, yeah. Enough of that.

And I figured it was time to just refresh our collective memories on why we use leaves in the aquarium...and what their real and alleged benefits are! And just some thoughts on them in general.

The most important parts of the Catappa tree to us fish geeks, of course, are the bark and particularly, the leaves, which contain a host of interesting chemicals. The leaves contain several flavonoids, like kaempferol and quercetin, a number of tannins, like punicalin and punicalagin, and a suite of saponins and phytosterols. Extracts of T. catappa have shown some effectiveness against some bacteria, specifically, Plasmodium, and some parasites as well. 

When Indian almond leaves are subjected to degradation in water, humic substances are formed, which, in turn, lower the pH of the water. The tannins are what color the water the beautiful brownish color that we geek out about so much around here!

There is also anecdotal evidence and theories 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- a most interesting benefit for the urban fish keeper, I might add. As a curious side note, blackwater streams and rivers are acidic, resulting in an aluminum concentration greater than that of "white waters", which have a more neutral pH. 

"Okay, Scott. That sounds very scholarly, but what exactly are those things and what can they do for my fishes?"

First off, I admit freely that I'm no scientist. I'm a hobbyist with a slightly higher interest in aquarium science than the typical human, and yeah, I had my share of biology and chemistry in college. But I'm no expert. That being said, I'll share with you what I know in concise, hopefully intelligible language!

Well, lets start with the flavonoids. Flavonoids have been shown 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. Kaempferol, a noted flavonoid,  is thought to have anti-inflammatory and antioxidant properties. Hmm...could that be why Betta fanciers used them for so many years after fighting their fishes?

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 see some potential benefits here as well.

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 merely because fishy authors touting the benefits of Catappa leaves love to throw them out there. 

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 makes sense that they are of benefit to fishes!

A cool government fisheries study in Thailand with Tilapia concluded  that Catappa extract was useful at eradicating the nasty exoparasite, Trichodina, and that the growth of a couple of strains of Aeromonas hydrophila was also inhibited by dosing Catappa leaf extract at a concentration of 0.5 mg/ml and up. In addition, this solution was shown to reduce the fungal infection in Tilapia eggs. 


Well, that sounds pretty cool!

Only problem with the findings from the study is- and I'll be the first to admit this- most of us don't have the equipment/capability to easily determine the level and/or purity of how many  mg/l of Catappa leaf extract is dissolved in our water, so we may have to rely on the completely anecdotally-derived "recommended" number of leaves per gallon as determined by long-time users of the leaves. Meaning, we estimate based on our gut and the results we're getting...

So the "generally accepted" dose for these leaves is subjective, at best.  You ask twenty people, you'll get 19 different answers. We have our favorite, but it's not about "therapeutic dose"- it's more about aesthetics. We go with typically like 4-5 small leaves- we're talking like 3" (7.62cm) or less- for every 15 gallons/60 liters...there is no real "rule of thumb" here. You an go more or less as desired...

Nonetheless, the leaves do have some science-backed therapeutic capabilities, as touched on briefly above, and their usefulness in helping hobbyists to safely replicate the conditions of blackwater environments in their aquarium is widely known in the hobby. These streams and rivers are fascinating subjects for recreating in our aquaria and they've launched our lifelong obsession with this interesting niche. A blackwater stream or river flows through forested swamps, wetlands, and flooded forest floors. As the vegetation and botanical materials optioned in these features decays, the tannins bound up in these materials are released into the water, making it transparent, acidic, and darkly stained, looking like coffee or tea!


If you're trying to mimic conditions of  blackwater streams and rivers, Catappa leaves can certainly help, as we've repeatedly discussed on these pages- along with a variety of other leaves. The breakdown of these leaves in closed aquarium systems mirrors what happens in nature, and offers many possible benefits for fishes that come from waters that are soft and acidic.

Blackwater rivers and streams have different chemical composition from "whitewater" environments, which has lead to the formation of flora and fauna that differs significantly from what are found in other types of waters. One study showed that blackwater rivers have large numbers of organisms like rotifers, but fewer crustaceans and mites. You won't find a snails to any great extent in blackwater systems, because it is difficult for them to build their shells in these calcium-poor environments. 

Sodium, magnesium, potassium and calcium are found in much lower concentrations in blackwater systems than in other types of water, and with minimal amounts of dissolved ions, the water has much lower conductivity than you'd see in a "whitewater" system. Blackwater rivers like the Rio Negro are incredibly high in fish biodiversity, and it's estimated that they are home to over 700 known species, with around 100 being endemic to this river environment!

The potential health benefits for fishes residing in carefully-controlled "blackwater" conditions are numerous, ranging from greater disease resistance to increased spawning activity, and, as documented in several studies, higher-yielding hatches with less incidence of fungal outbreaks in egg clutches.

So, all pretty cool stuff!

I hope this little meandering reminder about some of the real benefits of Catappa leaves and the blackwater environments they can help simulate will encourage you to do a little personal experimentation with them. With quality Catappa leaves and other botanical items readily available for experimentation, and the documented benefits they offer, not to mention, the cool aesthetics-there's never been a better time to enjoy "the tint!"

Stay engaged. Stay excited. Stay creative.

And Stay Wet.


Scott Fellman

Tannin Aquatics

Scott Fellman
Scott Fellman


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