It's funny in the hobby how that the more things change, the more they often seem to simply be evolutions from older practices. For example, the rearing of fish.
It all starts with food, right?
For pretty much as long as anyone caudal remember in the hobby, we've cultured living organisms to feed our fry after hatching. And, if you've been in the hobby more than a few years, you've likely heard of this valuable, easy-to-culture live food called "Infusoria."
Remember that word?
It's one of those aquarium world "catch-alls"; a sort of "throwback", if you will, from a "gentler, kinder era" in aquaristics. A time when under gravel filters, freeze-dried foods, and airmail of tropical fishes from Florida to your local airport were considered seriously badass, state-of-the-art, cutting edge things.
"Infusoria" may be described as a real "catch-all" term for small aquatic organisms, like euglenids, protozoa, unicellular algae, tiny invertebrates, and that are commonly found in freshwater environments, like ponds, creeks, and drainage ditches, used as a first food for tropical fish fry. Sometimes, it's referred to as "green water" in older hobby literature- an even more charming, albeit kind of vague descriptor!
In modern formal biological classification, the term "infusoria" is considered an antiquated, obsolete descriptor, as most of the organisms previously included in the collective term "Infusoria" are assigned to a different assemblage of taxonomic groups.
Nonetheless, it's a charming, albeit somewhat antiquated term that is still used in aquarium circles to describe the tiny organisms that arise when you soak some blanched lettuce, vegetable skin, or other plant matter in a jar of water. They're perfectly sized for young tropical fish fry as the first food when they are free swimming. In fact, at around 25-300 microns, these organisms are consumable by most fishes as soon as they've absorbed their yolk sac.
Yummy ( Well, if you're a little fish...)!
Sounds good, but how do you "make" the stuff?
Traditionally, it was done in the most low-tech way, which you know I love: You would take some blanched lettuce leaves, old flower clippings, hay, etc. etc. and basically let the stuff decompose in water, and after several days, a smelly solution of cloudy water will arise, driven by bacteria. Ultimately, after a few more days, the water will clear when creatures like Paramecium and Euglena arrive on the scene and consume the rampant bacteria population.
Voila! In theory, you have an "infusoria culture."
Well, yeah, but the problem is, the density of desirable animals to plain old water is pretty low when you culture this way, and you'll most likely be "feeding" your hungry fry with drops of stagnant water, little more. Kind of yucky...The more modern approach would be to obtain a pure starter culture of Paramecium from an online biological supply house (yeah, their are plenty of 'em- just do a Google search). Here's my fave. Paramecium average around 150 microns in size- perfect for free-swimming tropical fish fry!
You can use the aforementioned decomposing lettuce as a start, or you can elect to be a bit more clean and modern and use brewer's yeast (which comes in tablets) that you'd use at a rate of like 1/2 of a tablet to a 1 liter bottle. Sure, there are probably more exact numbers to employ, but this is a hobby, right? I'm sharing what worked for me, so your mileage may vary. You'd also use a few grains of wheat, which you can grab at the local health food store (or supermarket, for that matter) to help kick start things. Don't overdo either, as you'll end up with a much more stinky culture as a result. And in the hobby/life balance, "stinky"=bad. 🤔
Trust me on that!
You might notice a scum on the surface, and perhaps a bit of odor to the water...but you're an aquarist, so you're used to smelly wet stuff, right? And the water will take on a bit of a faint brownish or very light greenish color- totally normal.
After about 4-5 days, you should take a few drops of water from your culture (beneath the "surface scum") and examine them under bright light with a magnifier. You'll be able to see some little, tiny sliver-like "things" (I Know, a very scientific descriptor) wiggling around in the water. If you're hardcore like me, you'd look at them under your cool hobby microscope (a totally fun tool for the aquarist, BTW) for more accuracy!
This tells you it's time to rock and roll...you can feed your baby Tetras, Barbs, etc. right away, by dropping like 40-50ml of culture solution into your 5 gallon rearing tank. It's actually no big deal if you add more, because these organisms are harmless, and would naturally be found in water with fishes (albeit at a lower density). Since you're doing regular water exchanges in your rearing tank, you can minimize pollution along the way. Feed several times daily, and you'll be surprised how quickly the fry learn to recognize and attack them.
Sure, there is really not all that much involved in the process of raising "infusoria" than we've outlined here. Cultures of Paramecium are used extensively in labs to rear larval fishes, because they are an economical, nutritious option for newly-free-swimming fishes to feed on.
So, like many things in the hobby- the approach may have changed, but the idea remain the same- using whatever means we have at our disposal to create the best possible outcomes for our fish efforts!
Now, no discussion of rearing our little fishes would be complete without revisiting the idea of a botanical-influenced "nursery" tank for (blackwater) fishes for a number of reasons:
First, as we've discussed many times, the humic substances and other compounds associated with leaves and other botanicals, when released into the water, are known to have beneficial health impact on fishes. The potential for antimicrobial and antifungal effects is documented by science and is quite real. Wouldn't this be something worth investigating from our unique angle?
I think so!
Additionally, rearing young fishes in the type of environmental conditions under which they will spend the rest of their lives just makes a lot of sense. Having to acclimate young fishes into unfamiliar/different conditions, however beneficial they might be, still can be stressful to them.
So, why not be consistent with the environment from day one?
Finally-and this is the aspect we're going to focus on the most here- because it ties into the "infusoria" thing...the breakdown and decomposition of various botanical materials provides a very natural supplemental source of food for young fishes, both directly (as in the case of fishes such as xyliphorous catfishes, etc., and indirectly, as they graze on algal growth, biofilms, fungi, and small crustaceans which inhabit the botanical "bed" in the aquarium.
Now, this is pretty interesting stuff to me.
Everyone has their own style of fry rearing. Some hobbyists like bare bottom tanks, some prefer densely planted tanks, etc. I'm proposing the idea of rearing young fishes in a botanical-style blackwater aquarium with leaves, some seed pods, and maybe some plants as well. The physically and "functionally" mimic, at least to some extent, the habitats in which many young fishes grow up in.
My thinking is that decomposing leaves will not only provide material for the fishes to feed on and among, they will provide a natural "shelter" for them as well, potentially eliminating or reducing stresses. In nature, many fry which do not receive parental care tend to hide in the leaves or other biocover in their environment, and providing such natural conditions will certainly accommodate this behavior.
Decomposing leaves can stimulate a certain amount of microbial growth, with infusoria and even forms of bacteria becoming potential food sources for fry. I've read a few studies where phototrophic bacteria were added to the diet of larval fishes, producing measurably higher growth rates. Now, I'm not suggesting that your fry will gorge on beneficial bacteria "cultured" in situ in your blackwater nursery and grow exponentially faster.
However, I am suggesting that it might provide some beneficial supplemental nutrition at no cost to you!
And it's the same with that beloved aquarium "catch all" of infusoria we just talked about...These organisms are likely to arise whenever plant matter decomposes in water, and in an aquarium with significant leaves and such, there is likely a higher population density of these ubiquitous organisms available to the young fishes, right?
Now, I'm not fooling myself into believing that a large bed of decomposing leaves and botanicals in your aquarium will satisfy the total nutritional needs of a batch of characins, but it might provide the support for some supplemental feeding!
I'd take the concept even a bit further by "seeding" the tank with some Daphnia and perhaps some of the other commonly available live freshwater crustaceans, and letting them do their thing before the fry arrive. This way, you've got sort of the makings a little bit of a "food web" going on- the small crustaceans helping to feed off of some of the available nutrients and lower life forms, and the fish at the top of it all.
Now, granted, I'm romancing this and perhaps even over-simplifying it a bit. However, I think that there is a compelling case to be made for creating a rearing tank that supports a biologically diverse set of inhabitants for food sources.
The basis of it all would be leaves and some of the botanicals which seem to do a better job at recruiting biofilms- the "harder shelled" stuff, like "Savu Pods", "Jungle Pods", Coco Curls", "Capsula Pods", etc...I think these would be interesting items to include in a "nursery tank." And of course, they provide shelter and foraging areas and impart some tannins into the water...the "usual stuff."
Just another one of those ideas that would be fun to experiment with. Certainly not the "ultimate" fry rearing system...but I think one we have legit basis for playing with more and more.
I say to the breeder who may, for one reason or another, decided to use different foods- to give the "old school" method a try once in a while, not just because it works- but to help keep alive a direct link to the past of our fish keeping heritage, with a more modern approach applied.
And, for that matter, let's continue to push into some new ground with the "botanical-style nursery" approach, too!
Until next time, watch those little creatures swim, feed those fry...Go old school. And try a new twist, too!
Stay creative. Stay dedicated. Stay engaged. Stay devoted...
And Stay Wet.