What goes up must go down-thoughts on seasonal water fluctuation, food availability, and aesthetics

I know I talk/write incessantly about the seasonal inundation in Amazonia and elsewhere in the tropical areas of the world, and how they affect the water chemistry, food sources, and fish populations...but this stuff keeps going through my head! I wonder how we as aquarists can apply this information to our practices.

Amazonian seasonality, for example, is marked by river-level fluctuation, also known as "seasonal pulses." The average annual river-level fluctuations in the Amazon Basin can range from approximately 12'-45' /4–15m!!!  Scientists know this, because River-water-level data has been collected in some parts of the Brazilian Amazon for more than a century! The larger Amazonian rivers fall into to what is known as a “flood pulse”, and are actually  due to relatively predictable.

And of course, when the water levels rise, the fish populations are affected in many ways. Rivers overflow into surrounding forests and plains, turning the formerly terrestrial landscape into an aquatic habitat once again.

What can we learn from these seasonal inundations?

Well, for one thing, we can observe the diets of our fishes. In general, fish, detritus and insects form the most important food resources supporting the fish communities in both wet and dry seasons, but the proportions of invertebrates fruits, and fish are reduced during the low water season. Individual fish species exhibit diet changes between high water and low water seasons in these areas...an interesting adaptation and possible application for hobbyists?

Well, think about the results from one study of gut-content analysis form some herbivorous Amazonian fishes in both the wet and dry seasons: The consumption of fruits in Mylossoma and Colossoma species was significantly less during the low water periods, and  their diet was changed, with these materials substituted by plant parts and invertebrates, which were more abundant. Fruit-eating is significantly reduced during the low water period when the fruit sources in the forests are not readily accessible to the fish. During these periods of time, fruit eating fishes ("frugivores") consume more seeds than fruits, and supplement their diets with foods like as leaves, detritus, and plankton. Interestingly, even the known "gazers", like Leporinus,  were found to consume a greater proportion of materials like seeds during the low water season.

Mud and algal growth on plants, rocks, submerged trees, etc. is quite abundant in these waters at various times of the year. Mud and detritus are transported via the overflowing rivers into flooded areas, and contribute to the forest leaf litter and other botanical materials, coming nutrient sources which contribute to the growth of this epiphytic algae. 

During the lower water periods, this organic layer helps compensate for the shortage of other food sources. When the water is at a high period and the forests are inundated, many terrestrial insects fall into the water and are consumed by fishes. In general, insects- both terrestrial and aquatic, support a large community of fishes.

So, it goes without saying that the importance of insects and fruits- which are essentially derived from the flooded forests, are reduced during the dry season when fishes are confined to open water and feed on different materials. 

So I wonder...is part of the key to successfully conditioning and breeding some of the fishes found in these habitats altering their diets to mimic the seasonal importance/scarcity of various food items? In other words, feeding more insects at one time of the year, and perhaps allowing fishes to graze on detritus and biocover at other times? Is the concept of creating a "food producing" aquarium, complete with detritus, natural mud, and an abundance of decomposing botanical materials, a key to creating a more true realistic feeding dynamic, as well as an "aesthetically functional" aquarium?

This idea will make me even less popular with some in the so-called "nature aquarium" crowd, which, in my opinion, has sort of appropriated the descriptor while really embracing only one aspect of nature (i.e.; plants)...Hey, I love those tanks as much as anyone...but let's face it, a truly "natural" aquarium needs to embrace stuff like detritus, mud, decomposing botanical materials, varying water tint and clarity, etc. The aesthetics might not be everyone's cup of tea, but the possibilities for creating more self-sustaining, ecologically sound microcosms are numerous, and the potential benefits for fishes are many. 

It goes back to some of the stuff we've talked about before, like "pre-stocking" or at least attempting to foster the growth of aquatic insects and crustaceans, encouraging the complete decomposition of leaves and botanical materials, allowing biocover ("aufwuchs") to accumulate on rocks, substrate, and wood within the aquarium, utilization of a refugium, etc. All of these things are worth investigating when we look at them from a "functionality" perspective, and make the "mental shift"  to visualize what a real aquatic habitat looks like, and how its elegance and natural beauty can be every bit as attractive as the super pristine, highly-controlled, artificially laid out "plant-centric" 'scapes that dominate the minds of most aquarists when they hear the words "natural" and "aquarium" together! 

Learning more about the dynamics of natural habitats and the ecology of the surrounding terrestrial environments is just one fascinating and compelling area of study that we as aquarists can really get into. Yes, it requires some study. It requires trying some new and seemingly wacky ideas (encouraging the accumulation of detritus and epiphytic algal growth, for one thing), and embracing some different aesthetics. However, the potential for learning new things about our fishes, and perhaps being able to spawn them more reliably and productively, lessening our reliance on the collection of some wild specimens, could be significant.

Stay interested. Stay adventurous. Stay enthusiastic. Stay curious.

And Stay Wet.

 

Scott Fellman

Tannin Aquatics 

 

 


Scott Fellman
Scott Fellman

Author



Leave a comment