The right fish for the right aquarium...A case study of sorts...

We've talked a lot about creating aquariums to replicate specific's kind of what we do here, right? Super rewarding. Yet, it's even more fascinating and rewarding to design an aquarium around a specific fish sometimes.

Especially when it's one that you have coveted for so long, right?

We've all had that ONE fish which just sort of occupies a place in your heart and mind- a fish that-for whatever reason- bites you and never lets go, right? I think that every serious aquarist has at least one such a fish..

Here's mine...

Of course, it's also about the habitat.

As a lover of leaf-litter in our botanical-style aquariums, I am fascinated not only by this unique ecological niche, but by the organisms which inhabit it. I've went on and on and spoken at length about many of the microorganisms, fungi, insects, and crustaceans which add to the diversity of this environment. And of course, we've looked at some of the fishes which live there, too!

One of my all-time favorite fishes- and my absolute favorite characin is none other than the amazing Sailfin Tetra, Crenuchus spilurus!  This is a truly awesome fish- not only is it attractive and morphologically cool-looking, it has a great demeanor and behaviors which separate it from almost every other characin out there! 

It's almost "cichlid-like" in behavior.

It's definitely NOT the most colorful characin on the planet. But there is more than this fish than meets the eye.

It all starts with its intriguing name...

The Latin root of the genus Crenuchus means "Guardian of The Spring"- a really cool, even romantic-sounding name which evokes imagery-and questions! Does it mean the "protector" of a body of water, or some honorary homage to everyone's favorite season? Not sure, but you must agree that the name is pretty cool! In greek, it's krenoychos -"The God of running waters."

Yeah. That's the shit.

The Crenuchidae (South American Darters) is a really interesting family of fishes, and includes 93 species in 12 genera throughout the Amazon region. Most crenuchids are- well, how do we put it delicately- "chromatically unexciting" ( ie; grey-black-brown) fishes, which tend to lie in wait near the substrate (typically leaf litter or aggregations of branches), feeding on insects and micro invertebrates. And the genus Crenuchus consists of just one species, our pal Crenuchus spilurus, a fish which shares habits and a body shape that are more commonly associated with Cyprinids and cichlids!

That's just weird.

The Sailfin is an exception to the "drab" thing, and it's remarkably attractive for a very "simple" benthic-living fish. Sure, on the surface, it's not the most exciting fish out there, especially when it's a juvenile...but it's a fish that you need to be patient with; a fish to search for, collect, hold onto, and enjoy as it matures and grows. As the fish matures, in true "ugly duckling"🐥  style, it literally "blossoms" into a far more attractive fish.

The males have an extended dorsal and anal fin, and are larger and more colorful than females. Yes, colorful is relative here, but when you see a group- you'll notice the sexual dimorphism right away, even among juveniles.

Individuals spend a lot of their time sheltered under dead leaves, branches, roots, and aquatic plants. They tend to "hover", and don't dart about like your typical Tetra would. In fact, their behavior reminds me of the Dartfishes of the Marien aquarium world...They sort of sit and flick their fins, often moving in slow, deliberate motions.

The Sialfin feeds during the daylight hours, and is a mid-water feeder, consuming particulate organic matter, such as aquatic invertebrates, insects, bits of flowers, and fruits- the cool food items from outside of the aquatic environment that form what ecologists call allochthonous input- materials abundant in the botanical habitats which we love to model our aquariums after.

Yeah, we've written about that topic a lot...Trust me, that new "leaf vendor" who's trying desperately to rip off our style and vibe hasn't...'cause, oh, yeah... they just sell stuff and don't bother to write (ouch, a DIG! Yup.)...

Oh, back now from my ugly digression...

Further distinguishing the Sailfin from other characins is the males' parental care (yeah, you read that correctly!) of it's small (for a characin, that is) clutches of eggs (usually only like 100) and larval stages of the fish- characteristic more commonly associated with cichlids than characins! 

Are you interested yet?

I first fell for this fish as a kid, when I saw a cool pic of it in a well-worn copy of William T. Innes' classic book, Exotic Aquarium Fishes.

I was hooked from the start, especially when reading about the romantic etymology of the name!  And it just seemed so mysterious and unattainable, even in the 1930's...well, especially back in the 1930's, but it seemed downright exotic! And then, tying it together with my love of those leaf-litter-strewn habitats, it was a combo which I couldn't resist!

I never got this fish out of my system, and it took me like 30-plus years of being a fish geek to find this fish in real life. And, you know that I jumped at the chance..So worth the wait! The Sailfin is one of the most engaging and unique fishes I've ever had the pleasure of keeping!

Oh, and they are known to "vocalize', producing an audible "clicking" sort of sound that you can hear outside the aquarium...A very interesting phenomenon!

Although they are a bit solitary in nature, I've found that they've done really well in groups, sometimes forming loose aggregations within the confines of the aquarium, hovering over the leaf/botanical bed, waiting for food. And they have a sort of social order that only they seem to understand, but it's very evident. A fascinating set of activities which makes them even more interesting-and endearing!

Sailfins might be a bit shy initially upon introduction to the aquarium, as these fishes are cautious, rather "sedentary" characins, and don't swim quite as actively as other characins. Getting them to feed regularly in the aquarium- while not difficult- may be a bit of a process, as they are cautious fish, and tend to not stray too far from the botanical cover.

If you have other, more active Tetras and other fishes in the aquarium, they'll be a bit more tentative at first. However, these are decent sized fishes that will eventually overcome their initial shyness, and move confidently- if not slowly-throughout the aquarium.

Once you keep this fish, you'll just sort of "get" it! They're one of the most perfect fishes for the botanical-style, blackwater aquarium, and will fit right in to a well-thought-out community aquarium of smaller fishes, like the less "hyper" Tetras, dwarf cichlids, and catfishes.  They're perhaps one of the only characins which we can say has a real individual "personality!"

Yes, my photos suck. And yes, I am geeked out about this fish. And, need to try them. And yes, if you do, I'll hit you up for better pics! 😍

If you're looking for that "it" fish that will really make your botanical-style aquarium "pop"- adding a real presence and interest to the habitat you've created- give some real consideration to this wonderful fish- if you can find it! 

Trust me, having the "Guardian of The Spring" in your aquarium is worth the wait! Your leaf litter aquarium needs this fish! 

Yes, we all have that one fish. It's what keeps us passionate about the hobby; keeps us going. Keeps us dreaming, striving, searching.

Find yours.

Stay diligent. Stay resourceful. Stay passionate. Stay relentless...


And Stay Wet.


Scott Fellman

Tannin Aquatics 

Scott Fellman
Scott Fellman


3 Responses

Christopher Scharpf
Christopher Scharpf

August 12, 2023

The “Guardian of The Spring” etymology is apocryphal. It’s actually a combination of crena (Latin), notch, and nucha (Medieval Latin), nape of the neck, referring to notch at nape (of breeding males only?. Check out your well-worn copy of Innes. He says basically the same thing, and his photo clearly shows the notch.

Scott Fellman
Scott Fellman

April 22, 2021


Best.Fish.Ever. It’s one that only geeks like you and I seem to get- but once you see these fish, you GET them!



April 21, 2021

Great article. I too love these tetras. I have a male and 4 females, and although it took a year of keeping these fish before the male developed his amazing fins, I found it definitely worth the wait.

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