A Fish Called (giant) Oto
The Giant Oto, aka Otocinclus Gigante Catfish, is actually, not really an Oto. Which does explain why it gets about twice as big. They look like the popular and relatively common aquarium fish we call an Oto, but this fish is actually in a different genus (Hypoptopoma). They act very similar and have similar diets to most of the known Otos, but instead of maxing out at around two inches long, Otocinclus Gigante appropriately gets to be almost four. There are a couple fish called Oto (that aren't actually) and they get mixed up all the time. Luckily, they all seem to have the same needs, habits and habitats.
Like all the Otos, Otocinclus Gigante is a remarkable aquarium fish, especially for planted tanks. They have a ravenous appetite for algae, and are unlikely to bother your plants much, if at all. They are hardy and peaceful. When present in sufficient numbers will develop a school or shoal in the aquarium. Because they are a schooling fish naturally, they should always be added in groups. We suggest five or more, but you should consider 3 a bare minimum. When added in larger numbers, they will acclimate more quickly and be much more active. Giant Otos can be somewhat skittish on first arrival in a new display; adding more of them at a time will help them get past this quickly.
As far as aquariums go, hobbyists should think about 20-gallon tanks being a minimum for the smallest group we recommend keeping. They are big for Otos, but still relatively small fish. Obviously larger groups need larger tanks. They love planted environments, rich in driftwood and other graze-able surfaces. Substrate should be fine as they will undoubtedly ingest some as they graze, and we want them to be able to pass it. They come from water that is mineral poor, clean, slow flowing and warm. Try to mimic this in your home aquarium. Tank temperature should be in the mid 70s, with good oxygenation.
Feeding Otocinclus Gigante is a pretty easy affair. They are grazers in the wild, consuming primarily algae but also some plant matter. Keep this in mind when choosing foods for them. Their vegetarian diet can be emulated with algae wafers and blanched vegetables. If the display is rich in algae, they will need less feeding than they will in a clean aquarium. If you feed them blanched vegetables, be sure to remove any uneaten food at the end of the day to prevent it from decaying. In house we feed them Nutramar Freshwater Algae and Color Boost Shots. These are great because they offer a perfect profile for these fish (and other herbivores) and we can stick them to the bottom or the glass where the Giant Otos would usually be looking for food. They take this food greedily and are doing very well on it.
Despite their Pro-Wrestling sounding name, Otocinclus Gigante is a very peaceful fish and as such should be kept with other animals of a peaceful nature. Tetras, Barbs, Angels, Discus, even Guppies are good tankmates in the right display. If you have, or are planning a peaceful community display, (especially an Amazonian one) Giant Otos are an excellent choice for adding. As they are grazers by nature, and not that aggressive when it comes to food, make sure you choose tankmates of a similar mind, or that you make food choices to allow them to eat easily. We've seen some recommendations that say you can keep them with ornamental shrimp, and while this is likely true, these two animals have the exact same diet and will be in competition with each other for food.
Unlike the smaller Otos, Otocinclus Gigante is not yet being bred in captivity. This means that they are somewhat rarer than many other Amazonian algae eaters you may find in your Local Fish Store. We have no doubt that it won't be long before these fish are available on an aquacultured basis, for now, their wild harvest is very sustainable. It is also very important to the wellbeing of the local fishermen who cannot compete with the domestic aquaculture operations that have replaced the wild harvest of many, if not most, popular aquarium fish. If you're interested in trying your hand at breeding the Giant Oto, an opportunity awaits! As a model, the true Otocinclus reach sexual maturity within the first year. They are then brought into breeding condition by ensuring an overabundance of food, increasing the protein in their diet and raising the water temperature. Females lay eggs on plants and other natural substrates, the eggs hatch within a week or so. The fry feed on algae, and so success in rearing them would be enhanced by removing them to an alga rich, but competition poor environment.
If you're looking for a rare but peaceful shoaling fish that decimates algae (and has a really excellent name), then Otocinclus Gigante is a great choice for you. They are hardy and easy to keep, making them appropriate for hobbyists of all experience levels. They also offer the advanced hobbyist the opportunity to breed an ornamental fish that few, if any people are successfully breeding (at least at scale) at the time of this writing. Sound like something you're into? Head to your LFS and tell them that Aquatropic has some Giant Otos you want to get into your fish tank!