February 13, 2017

Know thy neighbor: Lessons from nature on fish community composition.

We spend enormous amounts of time trying to create interesting, colorful, and harmonious fish communities; it's not only fun to do, but it's essential to creating a successful aquarium. Everyone knows that a properly-selected group of fishes will create an environment that achieves all of these objectives and more. We do all sorts of research to figure out the best combinations.

For some, it can get really overwhelming- sorting through all of that literature and ferreting out suggestions from other hobbyists!

There is actually a better "source" to turn to...Ask yourself this:

Couldn't there be some information we could glean by looking at naturally-occurring fish communities in our target area? I think so! Let's take a brief look at a community of fishes derived from a study which took a random sampling of various Amazonian igarape habitats, and consider how the findings could help create an interesting assemblage of fishes for our aquariums! Now of course, in my typical hobbyist's zeal and sloppy research fashion, I took great notes but forgot to write down the name of the study... urgggh! :(

First off- some interesting facts!

In the sample area, the average depth of the leaf litter was an astonishing 80cm (about 32 inches) deep! That's some serious deep leaf litter! Especially considering an average water depth of 49cm (about 19 inches)! That's a very interesting "substrate-to-water-column ratio", wouldn't you say? And the interesting thing is that, while there is some seasonal variance in the water depth of the habitat (about 15cm/6inches) during wet and dry seasons, the leaf litter depth at most varied by about 6cm (2 inches) during the seasons. The pH of the water varied between 4.1-5.29 in these locales.

As one might imagine, areas of greater water depth yielded a greater number and variety of specimens.

Here is a grouping from one of the sample locations that is very representative of the types of fishes you'd find in such an environment:

Crenuchus spilurus

Nannostomus marginatus

Pyrrhulina brevis

Iguanodectes variatus

Hyphessobrycon sp.

Hemmigramus sp.

Aequidens pallidus

Apistogramma steindachneri

Rivulus compressus

Obviously, not all of these species will be easily available at any given time, so you can, of course. "fudge it" a bit and throw in some similar species, such as other Rivulus or Apistos as need be, without changing the "flavor" of the community, right?

That's an interesting, primarily "characin-dominated" community, wouldn't you say? If you notice, the assemblage includes shouting fishes, more "solitary" species, and fishes like the cichlids, which establish their own social hierarchies-as well as the Rivulus, which often aggregate in groups on the fringes of the slower-current pools of the igarapes in the study.

I could easily envision an interesting community of little fishes derived from this list, occupying all different strata of a botanical-influenced, blackwater aquarium. The neat thing here is that you have fishes with a variety of shapes, sizes, colors, and habits all in a relatively small area. (these were captured in 3 meter by 2 meter/27 x 6 ft seines, to give you some idea of the sizes of the areas from which the samples were taken). Now, that's obviously a lot larger than even the largest home aquarium, but the relative proximity and variety of fishes in the given area is interesting! I think we could obviously "compress" this a bit and utilize a more-or-less similar combination of fishes in a realistically-sized home aquarium with some good amount of success!

There is obviously so much more to creating a harmonious community of fishes than just mimicking a group found in one study and convincing yourself that you've created an amazing aquarium! You obviously need to take into account the size of your aquarium, and even more- the physical "structure" of the aquascape. As alluded to in an earlier guest blog by Mike Tuccinardi, the physical attributes of our aquascapes are not just aesthetic in nature; rather, they provide the basis for natural behaviors, interactions, and the overall comfort of the fishes.

The open-water-shoaling Hyphessobrycon species need some space in which to swim, while the more "sedate" Crenuchus and Iguanodectes like to have some structures, such as driftwood or root tangles, to hide among. The cichlids are happiest with some access to the substrate, with other physical features, such as holly logs or large stones, in which to create spawning sites and establish territories.

The Rivulus like open areas of water surface, so that they may opportunistically feed on insects that fall into the water, and be able to (gulp) jump from pool to pool as the fish feel is necessary (obviously, a cover of some sort is necessary to discourage this "natural" behavior!).

By studying and considering various aspects of the natural environments and the aggregations of fishes which live in them, and interpreting and utilizing some or all of the information derived from them, it's very possible to create vibrant, compatible, and very functional aquarium systems!

Just another component of the "functional" aspect of the botanical/blackwater aquarium which can be applied to a variety of aquarium keeping situations. We see this approach taken in African Rift Lake cichlid community aquariums, and such logical stocking approaches go beyond simple aesthetics, so we have hobby examples of the success of replicating natural community compositions from various locales worldwide in the aquarium.