What is "mesofauna"? These are small organisms generally measuring from "0.3 mm to 18 mm" for the largest specimens and which frighten us the first time we see one or more in our tanks ^^!
However, it is these small invertebrates that are the first signs of a good balance in a tank when they start to be present. They are also a sign of the presence of " microfauna " (microscopic bacteria) which is also very important for the balance of a tank. The bacteria of the microfauna being the "main" food (and therefore not the only) of the invertebrates of the mesofauna, hence the fact "mesofauna = presence of microfauna".
These small animals also feed on the food of your axolotls (fish) which often seep into the soil. The most hard-working at this level being the "Stylaria lacustris and Aeolosoma variegatum" which are small long and fine white worms measuring up to 18 mm for the Stylaria and 5 mm for the Aeolosoma.
Their population in a tank will depend a lot on how you feed and the speed / amount of organic waste removal from your aquarium! You will therefore have understood that these small invertebrates regulate their population mainly in relation to the food they have at their disposal.
The highest overpopulation is often that of Stylaria lacustris (white grubs up to 18 mm long living in colonies)! To remedy this, lower the amount of food given and / or opt for a "feeding zone" this will prevent the infiltration of food into the soil and therefore less food for the Stylaria. You can dig a big hollow in the sand (this is how I do it regularly, to prevent the pellets from "flying" everywhere.
Here is now a census of the main small "good and harmless" organisms that you can observe at home in your bins:
Aeolosoma variegatum : 5 mm white worm that can be seen swimming in open water or wriggling on the windows of the aqua! It lives in the substrate and moves quite quickly. It also fears the light, which it flees when lighting the lamps!
Oligochaetes / Annelids : Oligochaetes are part of the subclass of annelids and are segmented aquatic invertebrates with a worm-like appearance. The leech or the earthworm for example are annelids !! A ringed body, made up of successive segments in which are repeated common internal structures (muscles, nerve ganglia, nephridia, etc.) located in a coelomic cavity which acts as a hydroskeleton. If the population of these worms increases very quickly, this can be due to a "polluting" soil (too much waste), too little filtration, overfeeding, a lack of oxygen in the tank or overpopulation !! So if you see one of his little critters, watch out for their numbers to not increase too much! if this is the case, to remove them, it suffices to remove them which is relatively simple compared to their size (between 5 and 8cm). They feed mainly on bacteria or dead organic matter (detritivore).
macrostomum lignano : "transparent" flatworm of 1.7 mm in adult size belonging to the family of "Plathelminthes" and not "CILIATES" as many think !!! It is hermaphrodite, lives in the substrate and aquatic plants but when you notice it it is often on the windows of aqua! Like the planar, it has the ability to regenerate its cells. "Some species of macrostomum can reach a size of 5 mm"
Paramecium (infusorium): transparent worms belonging to the family of "ciliated protozoa" of size between 100 and 300 µm therefore between 0.1 mm and 0.3 mm using their cilia to move and feed! It will be the most frequently encountered "ciliate" in our tanks. Paramecia are also bred "en masse" to make "live prey" for fish fry. In our aqua, you will be able to observe them most often on the windows! You will understand, the "ciliates" owe their name to the "eyelashes" allowing them to move!
Ostracods : Crustaceans of the "Arthropodas" family whose body is enveloped in a "shell". Those found in our bins generally measure between 0.5mm and 3mm. resembling a small bean that swims all over the place, and can become invasive when it has no predator! But it is never dangerous. It feeds on detritus Most are benthic (lives near the bottom), swimmers, crawlers or burrowers on the bottom or on plants. Some are pelagic (live at the depth closest to the surface). They feed on organic debris of all kinds. They live at an ideal temperature of 18 ° to 23 °. Sensitive to abundant food, if you overfeed it will cause ostracod numbers to explode. So just like Stylaria, if you want to reduce the ostracod population, you will need to reduce the amount of food given.
Copepods : Small crustaceans of the "Cyclops" family of size from 0.5 mm to 5 mm (closer to 0.5 mm for those in our tanks). Unlike the "Ostracods", they do not have a shell and have only one central eye (except the copepods of the genus Corycaeus which have two large cuticles, a pair of magnifying glasses to form a telescope)! Copepods can be pelagic (living near the surface) as well as benthic (living near the bottom). They feed on cells with low protein content (detrital foods) and on the other hand, by succeeding in exploiting the richness in proteins of cells which are difficult to digest such as dinoflagellates (phytoplankton organisms), they know how to use cyanobacteria, etc.
Photo 1 = female carrying her eggs
An algae, a fungus, a mold?
It moves very slowly, autonomously and not just carried by the current ... and proliferates rapidly
It is a protozoan that moves to find its food, half mushroom, half unicellular plasmodium; We sometimes speak of collective amoebae.
A sort of lower "mushroom", which is sometimes aquatic, and mobile at some point in its development.
It is absolutely harmless to the aquarium…. but to get rid of it you can use an anti-fungal containing copper, but be careful that this will also kill the invertebrates of the tank and damage the liver of the axolotls. So you might as well keep it, it looks pretty after all?
In its growth phase, it resembles a voracious giant amoeba that unfolds like a fan, enveloping everything in its path, and able to digest whatever it encounters: bacteria, spores and decaying organic matter.
Ferrissia (common name, freshwater limpet)
arrive with the plants. They are discreet because of their small size and do not present any nuisance in our bins, they look like the Chinese Hats of the seaside but in much smaller.
The shell is almost translucent white and slightly conical.
The body is rather in shades of gray.
Although belonging to the pulmonate family, respiration is essentially cutaneous. So they don't necessarily need to come to the surface to breathe.
Indicator of the absence of predation. Presence infrequent, often in young tanks.
Given the small size of this species, despite browsing windows or leaves of plants, no utility.
No nuisance in the aquarium.
Let's say that these animals are part of the microfauna that arouses little interest in general in our freshwater tanks.