Feeding Otocinclus

otocinclus vertical


As mentioned in the introduction page... a fat oto is a happy oto. An otocinclus should never be gaunt or have a skinny stomach. If it does look skinny, then something is wrong. Otocinclus are herbivores and they need to be constantly grazing on green matter in order to survive. Most tanks do not have enough algae to sustain a group of otocinclus so it is up to the fish keeper to provide supplemental food on a consistent basis.

Soft Green Algae

The main food of Otocinclus is algae. They will eat the soft green algae that grows on the surfaces of the tank and its contents. This surfaces include the inside of the tank walls, gravel, decorations, and plants. This soft algae isn't to be confused with green spot algae that you can barely get off with a razor blade. It's obvious that the rasping power of the otocinclus mouth isn't strong enough to remove that type of algae.

They also eat brown diatom algae, which is common in newly setup aquariums. Some have reported that they will really go to town on this algae and rid a tank of it in days. My soft water doesn't seem to produce much of the brown algae so unfortunately I haven't witnessed this firsthand.

So how can we grow this beneficial algae that otocinclus like? Well, we need to have an environment that is conducive to plant life too. Light and nutrients are important first steps. (More on this in the Happy Oto Tank article... coming soon.)

It seems that algae is the preferred food of otocinclus catfish. If they ignore all the other types of food you offer in the tank, there is a chance they may be getting enough from the algae itself. It's a good idea to first give them a while to notice what you've left in the tank as food, don't remove it right away. But as always, let their tummies be the guide!

Prepared Foods

There are products out there which people have tried with some success. One of the most common types are Algae Wafers which are sold in most stores. Hobbyists have often reported that their otos go for these on a regular basis. This may be a good food to use while acclimating the otocinclus to your tanks. The most important thing to pay attention to when feeding sinking foods is that there can't be any major competition for these algae tablets. Perhaps some gentle corydoras catfish won't be a major problem, but plecos or adult siamese algae eaters may prove to be too aggressive for these timid little fish to feel safe at the bottom.

There are also dried sheets of marine algae available for purchase. It's just like the material used for sushi rolling! Attach it to a clip or weigh it down with something first as it has a strong tendency to float. It bothered me that this food was meant for saltwater fish (all pictured on the label), and the question of salty-veggie matter struck me as a potential problem. Would the otocinclus have problems with the amount of salt in the seaweed sheets? I've contacted the company that distributes one of these products, and questioned them on the use of this for freshwater fish. Here is their reply: "...our algae is 100% natural dried seaweed and that it does contain salt, however it's safe for freshwater fish." Well, there you have it!

Green Veggies!

We can supplement an oto's diet with vegetables from the supermarket. Every fish is different, and some will flock to one vegetable type and shun another. It's important with all vegetables to wash them completely and make sure they are free of pesticides. Some of the more common vegetables to feed:

Preparation of the vegetables is a matter of taste and your experience of what works the best for your fish. What I have experienced is that the otocinclus will ignore a fresh vegetable in the tank, but once it has been in there for 12+ hours or more then it registers as food. My current theory is that after time the vegetable matter deteriorates to a point where it gets a little mushy and is more palatable to the rasping mouth of an otocinclus. One way to speed this along is the blanch/parboil the vegetable. Usually 30 seconds in a microwave while sitting in a small dish of water will be good enough to soften the vegetable. Cooking it will also help it sink sooner and much more easily.

Instructions for the delivery of vegetables is pretty much universal. We need to weigh down the vegetables so it can stay in one spot long enough for the otocinclus to reach it. Floating vegetables will mostly go unnoticed unless you have very little surface current to move the food around with, and even then my otocinclus rarely go up to the top of the aquarium tank walls. You can use "Veggie-Clips" sold in most fish stores to attach vegetables to the side of the tank with a suction cup. You can also use a rubberband and attach it to a small rock which is then placed on the bottom. Another method is to use leftover plant weights (the silvery strips that come with stem plants) and stick it in the vegetable to make it sink. I prefer the weights and sticking them into the vegetables, this provides more surface area for the otocinclus to suck on and cling to, but it's just a personal preference.

So how long should we leave these vegetables in the tank? Well, a good rule of thumb is to not let it sit in the tank for more than 3 days. You definitely don't want it to be in there when parts of it disintegrate and detach from the main portion; they may get lost, uneaten, and foul the water.


I once saw an otocinclus eat a rainbowfish egg. That's right, an egg! It was partially hanging out of its mouth, by a thread. Then in one quick motion it slurped up the egg and ate it. Yum! This may mean that otocinclus can digest protein, and even seek it out in certain circumstances.

This might also explain why there are sparse reports of otocinclus attaching onto larger flat-bodied fishes (such as Discus). It's still debated whether this is an intentional aggressive behavior or just the fact that they may be starving. The "slime coat" of most fish contain micro-organisms which are indeed palatable to other fish and this might be drawing the oto to it. Otocinclus will also seem to waste a lot of time cleaning off a side of the tank that doesn't have green algae on it... well it could still be eating something there, such as the micro-organisms which inhabit the bacterial film on all surfaces of the tank.

Some spawning reports spoke of feeding brine shrimp and blood worms to otocinclus prior to them laying eggs. I will most likely try this out on some of my own and see if they go for the worms or shrimp. Perhaps this is a trigger for the fish to begin spawning... ingesting protein-rich food.

(May 5th, 2004 update regarding Protein) Through correspondence with Dr. Scott Schaefer I've learned that the stomachs of wild-caught otocinclus exclusively contained algae and plant detritus. There was no evidence of other foods found in the system. This would lead me to believe that a protein diet is not necessary (and possibly unnatural) for the otocinclus to spawn.

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