When fishes disappear...

Okay, it's Monday, and I freely admit this is a really bizarre, and probably even morbid- topic.

However, it's something I've experienced for the- oh, 5 millionth time in my lifelong hobby "career", and it just sort of made me wonder:

Ever noticed how fishes sometimes sort of "vanish..." I mean, they hang on for a while- even appear to thrive...and then, like a breeze in the night, they disappear, never to be seen or heard from again?

Like, where do they go? What happened? HOW did they disappear?

Now sure, fishes don't simply vanish into thin air...However, they DO sometimes seem to just "stop coming out" after a while. Often, there might be some signs that something is amiss...you know, skulking about in the dim corners of the aquarium, not interacting with the other fishes, passing on food. 

Or, maybe not. 

Sometimes, a fish will simply be there one day, and gone the next. After months or weeks. And no trace.

It's weird, right?

Now, I'm sure that, should a fish die, it's acted on by bacteria, fungi, and any scavengers (like snail and crabs) which may be in the tank, and of course, or more disturbing to many- the other resident fishes.

But man, it's the act of "here today- goes tomorrow" that's kind of weird to me!

Like, what causes this?

Is there any way of knowing what is going on? Without overt signs of disease or injury, or being bullied by the other fishes in the tank...what do we have to go on? 

Usually, not much, right? 

And it can happen with a fish that seems to be perfectly healthy and happy, right up until the time it checks out. Smaller, shoaling fishes like Tetras and Rasbora, or even dwarf catfishes- are notorious for this sort of thing. One day you have a shoal of 20 specimens.  A week later, 18...Three weeks later, 14...Then 12.

What gives?

Is it nature's form of "programmed population control?" A way of assuring that only the proper amount of fishes, based on resources and space, survive in a given area? Or only the ones suitable for reproduction make it? I have read of chemical interactions between various schooling fishes, like characins, which alert others in the school to react if a member is injured or in distress- a sort of "chemical emergency alert system."

That makes a lot of sense. However, it doesn't do anything to explain the vanishings.

Why do they vanish?

Well, the reasons, or at least- or theories- behind this are many.

IMHO, the most common reasons are the usual ones:

Many of these are fishes that are recklessly caught poorly handled and fed along the chain of custody from river (or hatchery) to store (like, Otocinculus- the "Poster Child" for mysterious disappearances, or tint Tetras of various species...), and in such weekend condition upon arrival at the LFS or vendor that they’re barely viable by the time the hapless (?) hobbyist gets ‘em.

And of course, no one seems to quarantine anything these days, right?

So, they never have the chance to “fatten up” or recover from the rigors of their journey before being placed into a "community tank" with all sorts of competitors, dangers, and challenges…And they could be carrying some illness without overt symptoms, right? If you don't keep them in QT, you won't really have a chance to observe them over time to intervene easily.

Many of those which vanish mysteriously are not species that are strong swimmers or aggressive feeders to begin with (again, Otocinculus or Pygmy Corys come to mind). Or, on an individual basis, they could be weaklings of a more vigorous species. It’s literally “sink or swim” for many of these poor animals. Sure, some make seemingly good recoveries and settle in…for a bit.

Problem is, most of these fishes are so weak- perhaps (as in the case of wild or newly imported Corys, characins, and some Apistos) dealing with intestinal parasites, or even the after-effects of the collection and shipping processes- that there is little more they can do than “rally” for a while before taking their cue and exiting. 

Sad. Yet still a bit mysterious.

Now, many fishes ARE handled well. And they eat at the LFS…and perhaps even in your tank. And you might even quarantine them! They are finally released into your tank, yet take their "curtain call" anyways some weeks after introduction. Sure, some fishes simply die of natural causes. I mean, do you REALLY know how old that ONE Cardinal Tetra was?

Some fishes do have short lifespans- even the aforementioned Cardinals; thought to be almost an "annual" species in nature because of their environment. Could millions of generations of "genetic programming" simply be too strong to overcome even in artificially stable environments for some?

Well, this is certainly true for the annual killifishes, like Nothobranchius. Even the best care humanly possible isn't going to yield a 4-year-old Notho. 


Some diseases don't have visible external symptoms. And stress- the silent killer- affects fishes, too. And internal parasites are unseen, and can attack fishes over time- including those that seem to be well-adjusted and eating.

But they still take “the Stairway to Heaven”, as one of my fish-geek friends calls it- and bail quickly…or sooner, rather than later, at least.


Who knows?

Yet, each year, countless thousands of these types of fishes are sold…And the ones mentioned here are just some of the more common ones..There are thousands and thousands of fishes of different species that could easily fall into this “class”, so it’s not that unusual.

Okay, this is getting a bit depressing.

But it's something to think about. And to accept, to a certain extent. At least if we're not going to drive ourselves crazy cooking up exotic theories for their disappearance!

I mean, we certainly don't want to look at fishes as "expendable" in any way. However, we may simply need to come to the realization that, despite our best efforts, about all we can do is select good quality fishes, quarantine and acclimate them carefully, and provide the best food an environment possible -you know- the usual stuff-and accept the grim fact that some fishes are "pre-ordained" to disappear.

In the leafy, botanical- filled, deeply-tinted confines of a blackwater aquarium, the sense of mystery is only heightened, right?

Hardly satisfying. But a strange reality that anyone who's been in the hobby long enough comes to learn.

I wish I had an explanation.

I wish I had a sure-fire "workaround" for this.

Suffice it to say, there are a lot of things in nature- variables and such- which we simply cannot counter. About all we can do is to keep doing the best job that we can to provide a good environment for our captive fishes. Observe, learn, and wonder...

And occasionally, speculate about what happened when a fish disappears...

Stay positive. Stay curious. Stay devoted. Stay observant. Stay careful...

And Stay Wet.


Scott Fellman

Tannin Aquatics 


Scott Fellman
Scott Fellman


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