The myth of the cleaner fish: why your Corydoras and Ancistrus are always hungry
F. MattierThis is a scenario I know by heart. You go to a pet store to stock your first aquarium. The seller recommends a few colorful fish for the middle level, then inevitably adds: "and don't forget an aquarium-cleaning fish to clean the glass and a bottom cleaner for the waste." You leave confident, convinced that you have bought a biological cleaning crew.
As someone passionate about living things, I have to speak out against this purely marketing-driven concept. This famous glass-cleaning fish or sand scavenger does not exist. It is a highly effective commercial scam that relieves the buyer of guilt while mistreating the animal.
Do not feel guilty if you followed this advice! We have all fallen for it when starting out. But today, it is time to restore the biological truth for the well-being of our bottom-dwelling fish.
The Biggest Scam in the Aquarium Hobby
Let us begin with an immutable golden rule: no fish in the world feeds exclusively on excrement, waste, or grime.
A fish is a vertebrate animal with high metabolic needs. Selling it under the label of "cleaner" misleads beginners into believing that the animal will manage on its own with the leftovers in the tank. The result: these fish are often forgotten when food is distributed. Buying them to do the cleaning for you condemns them to die slowly and silently of starvation.
The Tragedy of the Pleco and the Hunger of the Ancistrus
The most tragic example of this trend is the fate of the Plecostomus. It is sold tiny and adorable at just three centimeters long, to scrub the glass of small 60-liter aquariums. Yet, for a pleco, aquarium size is a serious issue: this fish quickly becomes a 30- to 40-centimeter giant! Not only does it outgrow its tank, but it is also a very heavy polluter.
Its smaller cousin, the Ancistrus, often suffers the same fate. Contrary to popular belief, the Ancistrus does not feed by magically sucking clean glass. It is a vegetarian with a tendency toward wood-eating. This means it has a vital need for fiber to maintain healthy digestion: it absolutely needs a real piece of natural wood to rasp constantly, as well as a regular supply of fresh vegetables (zucchini, cucumber) or vegetable wafers. Without this, it wastes away.
Corydoras Are Not Scavengers
The second major victim of the trade is the Corydoras. Often sold as the ultimate bottom-cleaning fish, it is reduced to the role of a crumb collector.
Look closely at a Corydoras: this small armored fish has fine, extremely sensitive barbels around its mouth. They are not a broom, but a hunting radar! Corydoras are carnivorous burrowers with omnivorous tendencies. In nature, they plunge their heads into fine sand to uncover small worms, insect larvae, and micro-crustaceans.
If you see your Corydoras frantically sifting through your gravel from morning to night, it is not because they are zealously cleaning. It is because they are desperately looking for real food for corydoras and they are hungry!
A Fish Is Not a Detritivore
To understand this properly, we need to make a fundamental distinction in biology: a fish is a consumer (and therefore a polluter), not a recycler in any way.
A simple Platy or Guppy that spends its afternoon picking at microalgae on a leaf or pane of glass is doing exactly the same job as a so-called "cleaner." In reality, all fish rummage and peck a little, but none is designed to digest the pollution in your ecosystem.
The Only TRUE Aquarium Cleaners
If fish do not do the cleaning, who does? The real purification work is carried out by the silent biology of your tank: plants, invisible bacteria, and above all, the only true detritivorous organisms: snails and small crustaceans.
They are the unsung heroes! bladder snails, ramshorn snails, Malaysian Trumpet Snail, and water lice are designed by nature to consume dead leaves, inaccessible food scraps, and decomposing organic matter. They alone deserve the title of cleaners.
To restore the smiles (and health!) of your bottom-dwelling fish, you need to change your approach. Treat them as fish in their own right by offering them what they would hunt in nature. For Corydoras or loaches, nothing beats live worm-like prey that burrows into the sand or falls to the bottom, stimulating their natural hunting instinct.
👉 Give your burrowers a true hunting feast with our live aquatic worms (Blackworm, Tubifex).
Conclusion: Give Them Back Their Dignity
It is time to move beyond this destructive commercial myth. Do not ask a complex vertebrate to do the work of a snail, a water louse, or a bacterial colony. A bottom-dwelling fish is a fascinating inhabitant that deserves a targeted diet respectful of its biology. Entrust the cleaning to the real detritivores, vary the menus of your Corydoras and Ancistrus, and you will discover wonderful natural behaviors that hunger was preventing you from seeing!
Mattier
FAQ: Feeding Bottom-Dwelling Fish
What food should I give a Corydoras?
Corydoras need a diet rich in animal protein that sinks quickly to the bottom of the water. Quality sinking wafers (not vegetable-based) are a good foundation, but ideally you should give them live food. They love worm-like prey such as tubifex and blackworm, as well as enchytraeids and Grindal worms. These prey items fall directly to the bottom, where Corydoras hunt! This is an excellent natural food, extremely rich in protein. Beware of rumors: it is often said online that Grindal worms or enchytraeids are "too fatty." This is completely false! It is only their white color that gave rise to this unfounded belief.
The great advantage is that these worms are very easy to raise at home. With a ZollaBox Poisson S (for Grindal worms) or a ZollaBox Poisson L (for enchytraeids), you can set up a culture that allows you to have the best natural food available almost free of charge and at all times.
👉 Start your own live food culture with our ZollaBox Poisson.
What are the best cleaner snails?
For a healthy ecosystem, combining several species is ideal: bladder snails consume biofilm on surfaces and glass, ramshorn snails eat dead leaves and soft algae on plants, while Malaysian Trumpet Snail burrow deep into the sand to eat buried waste, helping prevent soil fermentation. This is the most effective natural cleaning team in the world!
Does an Ancistrus eat filamentous algae?
No, this is another frequent disappointment for beginners. Although it readily scrapes the encrusting green algae film from glass and decorations when young, the Ancistrus absolutely does not touch large filamentous algae or brush algae (black algae). Faced with an algae infestation, the Ancistrus will be of no help: only identifying the cause of the imbalance (light, nitrates, fast-growing plants) will solve the problem.