Taking stock: The idea of aquatic diversity, density, and the fish geek's remarkable ability to make things more complicated than they should be...

Have you noticed that, as aquarists, we tend to approach the stocking of our aquariums as an exact science of sorts?

Like so many hobbyists, I personally enjoy virtually every aspect of aquarium-keeping- yes- even water exchanges! However, one of the parts of this game that always drives me a bit crazy is developing and executing on a stocking plan! Now, it's not the aspect of, "I want more fishes than my tank can handle!" No, I'm pretty disciplined about that going in. With me, it's more of a question of, "Which of the 14 candidate fishes do I want to add to the tank?"

Is this a unique "Scott-Fellman-is-a-bit-wierd" problem, or do we all have this, to some extent? I suspect we all do...Okay, I HOPE we all do!

I mean, I generally know the types of fishes I want.

As you all probably know, I am a huge fan of characins, especially in my botanical-influenced "blackwater" aquariums. They are often found in these environments in nature. They're small fishes which aesthetically "fit" almost any-sized system and provide perfect "scale" for my aquascapes. I like them...no issues here. Where I run into difficulty is during that age-old debate: Let's say my tank can accommodate 50 characins of the size I am contemplating. Is it more interesting to have a dozen of four varieties, 16 or so of three varieties, or 10 of five varieties of characins? Or, do I just make it a "monospecific: tank and go for one large school of a single species?

Do I go for Rasbora instead of characins?


It's overthinking at its finest...and it's enough to make my head spin. It's the same with most varieties of fishes that we maintain in the hobby, isn't it?

Traditionally, I've taken the middle ground in stocking density.

I mean, this gives me a perfectly tolerable, yet still aesthetically-pleasing "ratio" of variety to "aesthetic bliss." Depending on the size of your display, I've found over the years that having numerous varieties of fishes in a modest-sized (or even a large sized) tank is actually kind of distracting! Seems like it's always nicer to have more specimens of less species.

If we think about how fishes are distributed in nature, does it support this type of thinking? Well, not really..or sort of, depending upon how you look at it. In studies I've read on leaf litter systems in the Amazon region, a 200 square meter area was found to be home to about 20 different species of fishes! That's  surprising population density. Another researcher observed that Apistogramma are often found in nature at population densities of up to a thousand individuals in an area of less than 10 square meters!  That's a LOT of fish!

Now, in the case of the leaf litter studies, there is a reason for the species richness:

Utilization of different parts of the litter bed by different species. In the Apistogramma study it was similar, in that the fiefs were distributed throughout a leaf litter bed of almost  a meter deep! Obviously, our aquarium are a lot smaller, and few of us could duplicate 3-foot deep leaf litter beds (nor would few of us want to..). And if you extrapolate down the size of the habitat to aquarium dimensions, you'd be working with a lot of species in a relatively small space i the "diversity" model, or a hell of a lot of Apistos in the "compact population" model! 

And then there are those Lake Tanganyika shell dwelling cichlids...which live in huge aggregations in the shell beds...they sort of have their own model, right? I mean, they do really well when kept densely...So...

There are numerous factors that contribute to population diversity and density of fishes in nature. In captivity...very few, right? I mean, it's our call, limited by available tank space, finances...and in some instances, our relative audacity!

The reality for us is some sort of compromise. We need to juggle aesthetics, the ability of our aquarium to physically provide space for the given fish population, as well as the biological and mechanical filtration capabilities we can offer. Not to mention, the potential for aggression, predation, etc. is higher in such a densely-populated model.

So back to square one, right?

Yeah, for me, it is. I'm about modest numbers of several small species...It's the fish geek in me who wants maximum "bang for the buck", as they say. I am okay walking that delicate dance between what I want and what I can provide..And doing it in a responsible, ethical manner. And then there is always that one resident fish- or group of fishes, which develop an attitude towards newcomers, making the addition of anything kind of nerve-wracking...

I fantasize about the 500-fish school of Tetras someday as the sole occupant of a larger tank- but the reality is the fish geek in me finds that a pretty tough pill to swallow!

Arrghhhh...More tanks. The solution is more tanks. That's it.

So I'm now narrowing down my final choices for my home blackwater tank...seeing how many of which fish makes the cut. Yeah, that's my "task."

This is going to be interesting. And a bit agonizing...

Todays dissertation on density, diversity, and just me being a general pain in the ass.

Hope you have a great weekend.

Stay curious. Stay disciplined. Stay engaged. Stay creative. Stay patient...

And Stay Wet.


Scott Fellman

Tannin Aquatics

Scott Fellman
Scott Fellman


Leave a comment