When it comes to selecting fishes for my aquariums, I'm probably as weird as anyone else. I'll geek out about it for a while. However, I typically have a good idea what I'm going to add to my tanks long before they're set up. I'll typically design and build an aquarium around a specific habitat, ecological niche, or fish species.
The research process can take months- years even.
Yet, by the time I'm done, I typically know exactly what I want to add to my tanks, and stay "on plan." There's very little "editing on the fly" with me. I think it's a holdover from growing up in the hobby. As a kid with one or two tanks, I HAD to be disciplined about the fishes I selected. This sort of discipline has served me pretty well.
Of course, sometimes, the fishes that I want are very difficult to find! Remember my rantings about Crenuchus spilurus, the Sailfin Tetra...a fish that I spent decades waiting for? That's an extreme example, of course. Yet typically, this self-discipline actually creates short-term annoyances while I wait for my target fishes to become available! It's often has resulted in my fully 'scaped and prepared tanks sitting fishless for weeks before the first ones go in...
You can relate to that. I know that you can!
I am a huge fan of characins, especially in my natural-style, botanical-influenced "blackwater" aquariums. They're perfect for these tanks, as we've discussed many times. 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?
Same with Rasbora or other small fishes.
It's overthinking at its finest...and it's enough to make my head spin.
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 and configuration 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...well, distracting! Seems like it's always nicer to have more specimens of less species.
If we study how fishes are distributed in natural habitats, 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 and variety. 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 plays a huge role in the distribution of fishes in this habitat. In the Apistogramma study it was similar, in that the fishes 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 many of us want to..well, maybe I would, but...).
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 in 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...Social behavior and spawning play a huge role in their population density.
There are numerous factors that contribute to population diversity and density of fishes in nature. In captivity...very few, right? I mean, really 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. (Yeah, I hate that word, too)
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.
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 line 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, right?
So, you're doing a lot of mental calculations in this game!
I may fantasize about the 500-fish school of Cardinal Tetras as the sole occupant of a larger tank- but that's a pretty tough pill to swallow! Expensive, too! And the reality is, many of the fishes I like simply aren't found in such huge aggregations, anyways. They're often the realm of "fantasy aquariums" dominated by high-concept, yet decidedly unnatural aquascaping.
Arrghhhh...I simply need more tanks. The solution is more tanks. That's it.
To catch a lot of fish, you need a pretty big net...and a big tank to go with it!
Stay curious. Stay diligent. Stay resourceful. Stay patient. Stay curious...
And Stay Wet.