Weather? Or Not?

The deeper we go into the world of specialized, natural-style aquariums, the more unique opportunities arise to witness new behaviors in our fishes, and to achieve some interesting outcomes. One of the coolest ideas that I believe deserves more attention is the idea of manipulating environmental conditions in our aquariums to replicate the seasonal changes that take place in these environments in Nature.

It's hardly an earth-shattering idea, but I think that the concept of seasonal environmental manipulation as simply part of managing some types of aquariums deserves some additional consideration, because it can more faithfully reproduce the subtle changes in the environment of our fishes on an ongoing basis.

It's been known for decades that environmental changes to the aquatic environment caused by weather (particularly "wet" or "dry" seasons/events) can stimulate fishes into spawning. 

As a fish geek keen on not only replicating the look of our fishes' wild habitats, but as much of the "function" as possible, I can't help myself but to ponder the possibilities for greater success by manipulating the aquarium environment to simulate what happens in the wild.

Probably the group of aquarists who has had the most experience and success at incorporating such environmental manipulations into their breeding procedures is Corydoras catfish enthusiasts! 

Many hobbyists who have bred Corydoras utilize the old trick of a 20%-30% water exchange with water that is up to 10° F cooler (6.5° C) than the aquarium water is normally maintained at. It seems almost like one of those, "Are you &^%$#@ crazy- a sudden lowering of temperature?"

However, it works, and you almost never hear of any fishes being lost as a result of such manipulations.

I often wondered what the rationale behind such a change was. My understanding is that it essentially is meant to mimic a rainstorm, in which an influx of cooler water is a feature. Makes sense. Weather conditions are such an important part of the life cycle of our fishes.

With a greater understanding of some of the environments we attempt to replicate in our tanks, and a desire on our part to replicate the way they exist at different times of the year, many of us are starting to experiment with seasonal water level increases, botanical "pulsing", etc.

Still others attempt to simulate a "dry spell" by allowing the water quality to "degrade" somewhat (what exactly that means is open to interpretation!), while simultaneously increasing the aquarium temperature a degree or two. This is followed by a water exchange with softer water (ie; pure RO/DI), and "resetting" the tank temp to the tank's normal range of parameters.

The "variation" I have heard is to do the above procedure, accompanied by an increase in current via a filter return or powerhead, which simulates the increased water volume/flow brought on by the influx of "rain."


Many breeders will fast their fishes for a few days, followed by a big "binge" of food after the temperature drop, apparently simulating the increased amount of food in the native waters when rains come.

Still other hobbyists will reduce the pH of their aquarium water to stimulate breeding. And I suppose the rationale behind this is once again to simulate an influx of water from rain or other external sources...

Weather, once again. It's influence is wide-reaching and inescapable. 

And another trick I hear from my Cory breeder friends from time to time is the idea of tossing in a few Alder cones into the tank/vessel where their breeders' eggs are incubating. This decades-old practice is justified by the assertion that the alder cones possess some type of anti-fungal properties...not entirely off base with some of the scientific research we've found about the (allegedly) anti-microbial/antifungal properties of catappa leaves...

And of course, I hear/read of recommendations to use the aforementioned catappa leaves, oak leaves, and Magnolia leaves for just this purpose...


And of course, if we look at the natural habitats where many of our fishes originate, we see these seasonal changes having huge impact on the aquatic ecosystems. In The Amazon, for example, the high water season runs December through April. And during the flooding season, the average temperature is 86 degrees F, around 12 degrees cooler than the dry season.

And during the wet season, the water level in the streams and rivers can be between 6-7 meters higher than they are during the dry season! 

And of course, there are more fruits, flowers, and insects during this time of year- important food items for many species of fishes.

And the dry season?

Well, that obviously means lower water levels, higher temperatures, and abundance of fishes, most engaging in spawning activity. 

Any annual killifish enthusiast will tell you a dozen ways to dry-incubate eggs; again, a beautiful simulation of what happens in nature...So much of the idea can be applicable to other areas of aquarium practice, right? 

Yeah... I think so.

It's pretty clear that factors such as the air, water and even soil temperatures, atmospheric humidity, the water level, the local winds as well as climatic variables have profound influence on the life cycle and reproductive behavior on the fishes that reside in these dynamic tropical environments! I'm really enjoying experimenting with going from "dry season to wet season" in some tanks at the moment, and it's nothing if not fun! 

We've literally scratched the surface, and the opportunity to apply what we know about the climates from where our fishes originate, and to incorporate, on a broader scale, the practices which our Corydoras-enthusiast friends employ on all sorts of fishes.

So much to learn, experiment with, and execute on. And in Nature, we have the very best example of all from which to draw information and inspiration! 

Stay curious. Stay intrigued. Stay observant. Stay creative. Stay experimental...

And Stay Wet.


Scott Fellman

Tannin Aquatics 



Scott Fellman
Scott Fellman


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