Fishing around for fishes...

The neatest thing about tropical fishes is that there are so damn many varieties to play with, right? And within the different varieties are all sorts of species nuances, like temperament, dietary preferences, size, and interesting behavioral aspects. These nuances can often help us "discover" fishes that are actually well-suited for the types of aquariums that we play with.

Some DO find their way into our tanks fairly regularly...

Others tend to be more elusive. 

I wonder why I've been so obsessed with eh more elusive fishes over the years.

I guess it's because I was such a prolific reader of fish books growing up- or maybe, because I'm fascinated by the habitats from which some fishes come from, which has resulted in me researching and looking for some rather obscure fishes found in them. And the crazy thing is that many of them are simply not kept in the hobby at all.

Have you 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 those little bastards!") as to be almost "mythical"...

You know, like some of the really rare blackwater-dwelling livebearers, of which there are a few. Of course, they're just plain dull, and have so little commercial value that they are likely angrily tossed back by the native fishers because they foul the nets as "by-catch" while they're looking for some more interesting (read that, "saleable") fishes!

Makes sense. Economic realities often supersede our geeky obsessions...

Nonetheless, there are a surprisingly large number of livebearers found in environments we might be fascinated by. At least, enough species to "keep you on your toes", waiting, Watching, and wondering if they will ever show up in the hobby.

And there are the really unusual fishes:

One example?

Well, it's more of a group, really...Knife Fishes.. These are epic fishes, with all sorts of fascinating ones. Now, the "rap" on most of the Knives is that they get really large, are nocturnal, cryptic, predatory, etc...

And I admit that.  

Some simply get too large and hide like mad during pretty much any time of day you're likely to be in front of your aquarium. I don't know about you, but paying good money for a fish whom you might see the tail of, maybe three times a year- all the while, pandering to its specialized dietary requirements- can get old after a while, right?

However, they're my weakness...if there were ever a bunch of fishes I'd break my "no large fish" rule for (yeah, I f-cking HATE keeping large fishes), it'd be these guys. However, there are smaller ones...Yeah, you heard me. Ones that reach reasonable sizes; some of which don't even spend every second of their existence hiding...

Sure, I know my fave, the Black Ghost  (Apteronotus albifrons) will often become rather tame, and come out all hours. But hey do get kind of large...I give them a pass for their cool factor. 

Yet, there ARE others out there that fit my bizarre "requirements..."

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 considerably smaller than the big guys- the Clown Knife Fish, Banded Knife Fish, etc...

Many come from small rainforest streams, rivulets, even flooded forest areas and other habitats that we're kind of into around, 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...acclimating them, getting them to overcome their natural shyness- and feeding them at the right time of day (or night, typically)! 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!

Nonetheless, the possibilities are tantalizing, huh? 

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 geeks 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! 

They are often associated with marginal lagoons, and flooded grassy areas, which, as we all know by now, form when the aforementioned larger rivers overflow during the rainy season. 

Are these good fishes to keep?

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...

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

So, why do I have even the remotest interest in this group?

I like what they eat.

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 6 inches/16cm 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 Rays, myself)!

Yet, there are some smaller ones- some, like Chilodus punctuatus, the "Spotted Headstander", reach no more than about  3.14 inches /80mm in length! I've kept this species before In a botanical-style aquarium and really found them fascinating- and useful!

What I find fascinating about these little fishes, which tend to occur in both larger bodies of water- like rivers and streams, as well as the flooded forests and little blackwater tributaries we generally obsess over, is that they are typically very specialized feeders- detritivores, to be specific. And they also pick at biofilms on wood, rocks leaves, etc. 


I guess you might liken them to carp- fishes that will essentially eat just about anything...And some of them, like the little Headstanders I just mentioned- are social, and tend to shoal together as they feed!

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, right?

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

And Stay Wet.


Scott Fellman

Tannin Aquatics 



Scott Fellman
Scott Fellman


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