One giant leap...why fishes jump (out of aquariums, etc.) and the dilemma of the "open-top" aquarist.

Ever wonder why some fishes jump so well?

I mean, I've had Rivulus that could soar out of the smallest opening in an aquarium, like a Trident ICBM leaving a submarine launch-tube!

And being a lover of open-top tanks, it doesn't seem like I'll ever have any of my beloved Marbled Hatchetfishes (Carnegiella strigata) or "Splash Tetras' in my tanks.

(Splash Tetra, Copella arnoldi Pic by Zikamoi, used under CC BY S.A.-3.0)

Then again, I've had an Apistogramma do a "death leap" out of my open-top tank, too-so you can never be too careful, right? Fishes jump out of fright, aggression, etc...too many reasons to theorize. Obviously, if you're water smells like #$^&, there's a better-than-average chance that they're jumping cause the living conditions suck. And they're just hoping that "the next stream over" has better water.


Now, I know there are a lot of theories about how the Hatchets jump when they are freaked out or what not, but it's also commonly suggested that they use this jumping ability to catch flying insects. Now, insects, do, indeed comprise a lot of their diet, as confirmed by gut-content analysis, so it makes sense- but has anyone ever examined their vision? I mean, to be able to jump out of the water and pluck a flying insect mid flight is a serious feat for a little fish, and their eyesight must be extraordinary! I


In the case of  the "Mangrove Rivulus", Kryptolebias marmoratus, studies have shown that they can actually live for weeks- in fat, up to two months- out of water! (It did not play like this out for the various other species of "Rivs" I've kept over the years that went "carpet surfing") In the case of the hermaphorditic K. marmoratus, it jumps out of the water with a powerful tail flip, and cozies up in rotting mangrove logs, coconut shells, or whatever damp botanical environment it finds itself in after a leap!

During it's time out of the water, the fish's gills actually alter themselves so that the fish can breathe through its skin! Crazy! And this unique ability, coupled with it's legendary jumping capabilities, allows the Rivulus to get out of aquatic environments that have low oxygen concentrations or high levels of hydrogen sulfide, researchers discovered. An amazing survival technique, huh? Its  jumping abilities also enables the fish to flee predators and hunt for terrestrial prey, like flies and even small crickets.

Now, this is a bit of a variation on a theme as to the leaping abilities of some wild Betta species, which, as we've discussed previously, also jump out of bodies of water when they are becoming too unsuitable for continued existence. (i.e; the water is nasty!).

Sensing a theme here?

Now, I'm not suggesting to create a damp, foul-smelling "rain forest floor" of leaves, botanicals  and mosses in your fish room to accommodate the K. marmoratus as they jump...but that would be an interesting study, huh? Sorry, I was just going with it for a moment there...

And of course, the Climbing Perches and "Walking Catfish" are well-known for their terrestrial locomotive capabilities...but they're not really "jumpers"- and certainly fishes that you're typically gonna see on anyone's "wish list", being predatory, even invasive fishes with little redeeming traits from an aquarist's point of view! Nonetheless, it's interesting to ponder why these fishes leave the relative comforts of their aquatic environment for the big, cold terrestrial world, isn't it?

Back to the "problem children" we actually want to keep.

So how does the erstwhile fish geek who loves jumping fishes deal with them? I mean, finding dried out fishes on the floor sucks- especially hard to get ones like many Rivulus or Hatchets. It's not really rocket science.

Well, the obvious first  answer is to not keep the damn things in open-top aquariums!


But what fun would that be?

The suggestion given to me by a lot of "Hatchet lovers" (that sounds creepy, huh?) is to employ floating plants. Our emerging aquascaping superstar and "botanical BFF" Andrea Freel of Scotland keeps them in her open top tank, and does not experience "jumpers" when provided floating plants for natural cover.

Obviously, plants are definitely not 100% foolproof as a jump preventative, and you'll just have to "roll the dice", as they say. However, they are certainly the most attractive option, in my opinion. Our friend Tai Strietman, who's amazing botanical/blackwater tanks have graced these pages many times, also employs this technique with it's certainly worth the gamble, IMHO.

Of course, if you would rather use some "technical" method, you can always construct a barrier with fine mesh over a plastic frame cut to the dimesions of your aquarium. Not the best looking thing, but far more attractive than, say, egg crate and other physical barriers often employed for this purpose. And, you'll still get good light penetration and gas exchange! Reefers do this all the time...

You could use all sorts of nylon mesh materials, ranging from window screening to "rabbit fencing",  or the wedding-dress fabric called "tulle", which works well depending upon the size of the fishes you're trying to keep in. And, there are now some commercial options (like kits) available to do this...

And of course, in the end, you could do what I do...

Forgo the aforementioned jumping fishes and just be bitter and jealous of your friends who have 'em.

I DO like being bitter and jealous...but I think it would be more fun to have some Marbled  Hatchets.

Yeah, maybe I'll pay a visit to the fabric store.

Well...maybe not. I'll just stay bitter.

And you...?

Stay inventive. Stay inquisitive. Stay ready to catch your jumping Rivulus! 

And Stay Wet.

Scott Fellman

Tannin Aquatics 


Scott Fellman
Scott Fellman


2 Responses

Scott Fellman
Scott Fellman

January 07, 2017

LOL, Brian…It’s like a chain letter…My enabling fish friends tell me to go for it, and before I do, I tell a few friends, lol…

Brian Byers
Brian Byers

January 06, 2017

Oh Scott!! You have made me smile :-) :-)!!! I have floating plants and Lord have mercy, I have hatchetfish on my mind.You should’ve not printed this post. This is all the push I needed in purchasing hatchetfish for my open top tank. Mind you, if my fish jump ship, I coming to get your behind!!!

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