Algae Eaters for the Planted Aquarium

(Unedited version)
Originally appeared in the July 2005 issue of
Tropical Fish Hobbyist Magazine

In the planted aquarium, once you start growing plants the next hurdle is often how to stop growing algae. There are a lot of different ways to combat the algae problem. Some aquarists give up and grow an algae tank, some scrupulously clean and sterilize every plant and decoration that goes into their tanks in an attempt to keep every spore of algae out. Many hobbyists use herbivorous fish and invertebrates to help control the algae plague. This month I'd like to take a look at some of the algae eating fish commonly used in the planted aquarium.

American Flagfish

One of the most interesting of the fish used for algae eating is a native of North America. Found mostly in Florida, these are actually colorful killifish. Males in particular are quite bright with a metallic red, (greenish)-white and blue pattern that gives them the nickname of American Flag Fish. Females are less colorful. These attractive little fish have been in the hobby for well over 70 years.

Flags are undemanding in their requirements, though they prefer moderate to hard water, they will survive into moderately acidic water also. They can tolerate very warm water and are also quite at home in a cooler tank. They can even be kept outside year round in warmer, southern states.

Even though flags are killifish their behavior is very similar to many of the cichlids. They lay their eggs in nests on the bottom of the tank, cared for by the male. I've read of instances of them spawning elsewhere in the aquarium and of making nests in the gravel. Mine always spawn under a big pile of Java moss, which covers a large portion of the tank bottom. I've read of bullying by the males but mine live in a multi-generational 10 gallon tank, and I haven't noticed any problems with beat-up looking fish.

Like many of the algae eating animals they seem to prefer green algae to diatoms or red algae. Though I can say in tanks I've had with flags, there have been no algae problems of any type. I've read of them eating some aquarium plants but have never seen them eating healthy plants in my tanks and the plants in their tanks don't seem to be tattered or missing any leaves.

I've read some accounts of aggressive flag fish particularly the males. I haven't had problems with aggression, but I usually keep mine in species only tanks. I've also read accounts of flag fish being bullied by other fish in the tank. This is one of those times when it really pays to do your homework. Keep these fish with other fish of similar size and temperament in a larger heavily planted tank and you probably won't have trouble with them. Also be aware that breeding males are most likely going to be aggressive, particularly near their nest.

Ameca splendens

Another fish commonly used to help control algae is the livebearer Ameca splendens. The commonly available livebearers, guppies, mollies, platies and swordtails, are all Poeciliads. A. splendens are Goodeids. The most obvious difference between these two types of livebearers is in the shape of the male's anal fin. In the Poeciliads it's elongated to form the gonopodium. While in the Goodeids the male's anal fin is rounded like the females but has a notch along the back edge.


A. splendens have also been called the Butterfly Goodeid. The males have a bright yellow and black stripe along the edge of the tail. Females have dark spots along the body. Both fish have bright shining gold scales.

Like the flag fish A. splendens can be aggressive to other tank inhabitants. Be sure to choose tank mates carefully, and provide them with enough space and adequate plants too hide in. Being livebearers these fish are not difficult to breed but may be a bit more so than some of the more common Poeciliads. Gestation is longer, up to 2 months. There are fewer fry, though older females seem to have larger families. Female fish actually nourish the fry as they are developing through an umbilical cord like structure called a trophotaenia. Sometimes this can be seen still hanging from the new fry. The fry are large and there generally aren't problems with predation from parents in a well planted tank.

A. splendens will eat green hair algae and has also been reported to eat blue-green algae (Cyanobacteria). I couldn't quite believe it when I read it, so I tried putting some from another tank in with my splendens they seemed to start picking off it at first but then ignored it. After several days when the blue green algae started growing in the tank I removed it.

In addition to being good algae eaters these fish are critically endangered in the wild. Since the fish in the aquarium hobby are not being collected from wild fish, but being bred in captivity, keeping and breeding some in your tanks will also help keep these fish on the planet.

Oto Cats

Another fish popular for algae control in the planted aquarium is the tiny catfish Otocinclus, several different species of these South American fish may be offered, but they are similar. These fish are very small and modestly attractive, though not flashy in any way they have a dark stripe and a nice shape. Otos, as they are often called, like to live in schools and will sometimes breed in the aquarium. They look very nice in a large group sitting on the plants and decorations at the bottom of a tank. Otos lay eggs on aquarium surfaces like large leaves or the side of the tank. They are peaceful and shouldn't be kept with fish that are too large or aggressive.

Otos are said to prefer soft acid water, which isn't surprising considering their origins. They seem to be relatively adaptable though since I and several other aquarists I know keep them relatively hard and alkaline water.

In the planted aquarium Otos will eat some types of algae, generally the green encrusting types. They don't seem to eat hair, red, or blue-green algae. They will clean out the algae in most tanks pretty rapidly, keep it clean, and don't bother the plants. They will have to be given alternative foods, they need to eat regularly. A skinny Oto is a sad fish. Other foods that may be offered are zucchini, squash, cucumber, romaine lettuce, and spinach leaves. I usually use algae tablets or wafers, and sinking fish foods. They usually will enjoy a treat of tubifex or other small worms.

Otos can sometimes be difficult when first purchased. These fish are usually stressed from shipping when they arrive in your local fish stores, and many people report losses initially. I've had the same experience. They are reasonably hardy after acclimating to a well planted tank and as long as they're kept well fed.

Siamese Algae Eaters

The last fish I'd like to discuss this month is the Siamese Algae Eater. This fish, Crossocheilus siamensis, is a very useful algae eating fish from South East Asia. SAEs prefer to live in schools, and have not been bred in captivity. These fish are relatively peaceful, and have a nice size to them.

The best thing about SAEs is that they eat hair and red algae. I put 3 in to a 55 gallon tank that was having a great deal of trouble with hair algae over a year ago. They cleaned it out and kept it clean. They don't seem to bother plants either. As a bonus they have been reported to eat planaria. I haven't tested mine with that task personally yet.

The most difficult thing with the siamensis is making sure you actually get a C. siamensis. There are a group of fish that look similar, including the C. siamensis and fish from the genus Epalzeorhynchus. The C. siamensis was once considered part of that genus also. All of these fish are sometimes sold under several different common names including Siamese Algae Eater (abbreviated to SAE) and Flying Fox. The Epalzeorhynchus are often reported to be more aggressive to other fish in the tank when they mature, while true SAEs have better temperaments.

Questions or Comments?

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Welcome to the Jungle | Into The Forest | The Creepy Crawlies | A Clearing in the Thicket | Algae Eaters for the Planted Aquarium
North American Natives | Why things go wrong Pt 1 | Why things go wrong Pt 2 (Algae) | Algae Eating Shrimp | Lo-Tech Tanks
Welcome to the Fish Room | The Stemmed Plants | Mosses | A Livebearer Biotope | Planted Tank Social | The Genus Hygrophila | Cyanobacteria
Easy Plants | What I Did Last Summer | Decorations in the Planted Tank | Botany-An Introduction to Plant Biology | Botany-Anatomy of a plant
Botany-How Plants Work | Easy Rosettes | Going High-Tech | Floating Plants | Dealing with Success | Bringing the Outside In | Vallisneria
Hair Algae | Flowering Aquarium Plants Part 1 | Flowering Aquarium Plants Part 2 | Liverworts in the Aquarium | Elements of Design
Planted Aquarium Maintenance | More Mosses | Invaders | Ferns in the Aquarium | Setting up a Planted Aquarium
Seaweeds of the Pacific Northwest | Proserpinaca | Hardware for the Planted Aquarium | Rotala | Neocaridina Shrimp | Lo-tech Tank Tips

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