Coveted, but not kept...Yet.

Ever have a fascination with a fish that you absolutely know you'll probably never even keep? Or even see in the hobby, for that matter?

Yup, that's me! 

Some are so "hypothetical" (a term I hijacked long a go to mean, "Dude, you'll NEVER find these!") as to be almost mythical...You know, like some of the really rare blackwater-dwelling livebearers, of which there are a few...

And there are the really unusual fishes:

One example? Well, it's more of a group, really...Knife Fishes..Now, the "rap" on most of the Knives is that they get really large, are nocturnal, cryptic, predatory, etc...

And I admit that. 

However, their my weakness...if there were ever a bunch of fishes I'd break my "no large fish" rule for, it's be these guys. However, there are smaller ones...

Like the Hypomidae, aka "Grass Knifefishes"- 30 some-odd species in the Amazon region, only a few of which have found their way into the aquarium trade/hobby...The neatest thing about these fishes is that they are generally smaller than the big guys- the Clown Knife Fish, Banded Knife Fish, etc...

Many come from small rainforest streams and other habitats that we're, yeah! They tend to spend most of their daylight hours hiding in leaf litter (we can offer 'em that, huh?) and come out at night to go after the lights go out...And they like to eat insect larvae and small crustaceans, so providing the right kinds of foods isn't that hard.

The tricky part is obtaining the fishes to begin with...and feeding them at the right time! I'd imagine that creating an aquarium for these fishes would be challenge's the ability to enjoy them (ie; see them) when we want that could be problematic!

My "dream species?" A fish called Microsternarchus bilineatus. It reacts a length no larger than 4.75 inches/12cm...Can you imagine?

(Image by John P. Sullivan)

Yeh, I admit, I've NEVER seen this species in the hobby...likely never will. However, it's that chance of stumbling upon one that was collected as "by-catch" or whatever, which keeps busy like me excited and on the hunt for years.

I am also strangely fascinated by the Prochilodontidae- Like, the families Curimatidae, Prochilodus, etc. Larger, kind of "neurotic" fishes, some members of which can reach impressive sizes (like up to 30 inches/80cm or more!). They're found throughout the Amazon Basin.

And I'll be the first to tell you that they aren't the most colorful fishes you could keep, either! And, as mentioned above...many a freakin' huge!

What I find fascinating about these fishes, which tend to occur in larger bodies of water- like rivers and streams, as opposed to the flooded forests and little blackwater tributaries we generally obsess over, is that they are typically very specialized feeders- detritivores, to be specific.

They are often associated with marginal lagoons, which form associated with the aforementioned larger rivers. 

I guess you might liken them to carp- fishes that will essentially eat just about anything...

I mean, people keep Prochilodus species, and Semiprochilodus (the "Flag Tails"), and they do reach "respectable" sizes (like 15 inches/40cm) or more, making them possible long-term residents of truly large aquariums. I generally dislike large fishes...Or should I say, keeping large fishes in aquariums. I just have this thing about smaller fishes in larger tanks...

So why do I even have the remotest interest in them?

I like what they eat. 

(Prochilodus insignis -Image by Jutta234, used under CC-BY S.A. 3.0)

I love how they are serious detritivores. I find this type of feeder to be really, really interesting as a resident of a botanical-style aquarium, because they are adapted to processing the decomposing/mineralizing botanical materials as they are broken down by microbial and fungal action. 

This is a perfect type of fish to include in one of our systems, right? If only there were a smaller version!

Well, there ARE smaller fishes which consume detritus. What about the Hemiodus? These are social fishes, typically attaining much smaller size (like 12 inches or less), which feeding largely- though not exclusively- upon detritus, mud, filamentous algae, and some aquatic plants as well. And they're typically found in smaller forest streams, as opposed to larger rivers and tributaries...perfect residents for larger versions our style of aquarium, right?

They have been observed in nature following fishes like Sting Rays, snapping up various foods as the Rays displace the substrate with their activities. Oh, THAT could make for an interesting aquarium display for anyone who is into Rays. (And, as you might surmise- I have like zero interest in these big Rays, myself)!

Oh, and the Spotted Headstander... Chilodus punctatus, which I have maintained in the past few years..Cool fishes! 

It's fun to occasionally muse and consider the possibilities of smaller, or more "accessible" versions of some of these unusual fishes...

There are so many out there...

What's the one that keeps YOU looking, hunting, searching? Or, what are the available "analogs" that you keep?

Something fun to muse about on a lay Sunday, right?

Stay hopeful. Stay on the trail. Stay relentless. Stay dedicated...

And Stay Wet.


Scott Fellman

Tannin Aquatics 



Scott Fellman
Scott Fellman


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