Duckweed is a small, green, floating aquatic plant commonly found in ponds and aquariums. While some aquarists view duckweed as a nuisance due to its rapid spreading, others benefit by introducing fish species that feed on it. This article will explore the different types of aquarium fish that eat duckweed, the pros and cons of having duckweed in your tank, and how to manage its growth.
What is Duckweed?
Duckweed refers to the smallest flowering aquatic plant in the world. It floats on the surface of ponds and aquariums in dense colonies that look like a thick green blanket. The round or oval-shaped leaves are only a few millimeters wide, with tiny rootlets dangling underneath. Duckweed spreads rapidly through budding and can quickly take over the surface of still water environments. There are over 40 different duckweed species, the most common being Lemna minor, also known as common duckweed.
Benefits of Duckweed in an Aquarium
While too much duckweed can be problematic, maintaining a balanced amount comes with several advantages:
- Provides shelter and diffuse lighting for shy fish
- Absorbs excess nitrates and phosphates, improving water quality
- Additional surface area for beneficial bacteria colonies
- Source of food for plant-eating fish and invertebrates
- Provides breeding and spawning sites for certain fish
- Creates a more natural environment mimicking ponds
In moderation, duckweed can be an asset in planted aquariums. It is especially useful for breeding, hospitals, and tanks housing fry or delicate species. The shelter, foraging opportunities, and water quality benefits make it an excellent addition when appropriately maintained.
Potential Downsides of Duckweed
The main drawback of duckweed is its incredibly fast growth rate. A small amount can spread to completely cover the water’s surface within weeks under ideal conditions. Thick duckweed mats block out light, impede gas exchange, and reduce oxygen levels. As layers die and decay, potentially dangerous gases like methane can accumulate. Excessive duckweed is difficult to remove fully and often grows back rapidly.
Other potential issues include:
- It provides too much shade if unchecked
- Traps debris and hampers filtration
- It makes tank maintenance and feeding difficult
- Clogs filters and intake tubes
- Harbors pests like mosquito larvae
- Alters water chemistry as it decays
- It looks unsightly when overgrown
Fortunately, introducing duckweed-eating fish is an organic way to striking the right balance.
Fish That Eat Duckweed
Many fish species will nibble on duckweed, especially when they are hungry. However, certain fish have a particular fondness for duckweed and can help regulate its growth. Here are some of the top fish that eat duckweed:
Goldfish are a duckweed-eating machine, making them an excellent choice for controlling duckweed in ponds and aquariums. They continuously graze on plants and will devour floating duckweed. Fancy goldfish with wen growths or other anatomical issues may have some trouble, but common feeder goldfish are affordable. Remember their powerful appetites, as they may mow down more delicate plants.
Related to goldfish, koi fish also relish duckweed as part of their diet. These colorful carp forage along the water’s surface looking for tasty morsels. Koi thrive when offered a varied diet including duckweed. Their energetic feeding helps limit duckweed spread. However, koi grow quite large, so they need substantial space.
Many catfish are omnivorous bottom dwellers that will eat sinking duckweed. Corydoras, otocinclus, plecos, and other suckermouth catfish will happily rasp off duckweed when foraging. Upside down catfish are especially helpful, as they patrol the surface at night. Consider the adult size, as large species like pangasius may eat duckweed but become unmanageably big.
Like angelfish, African cichlids and South American cichlids snack on duckweed floating above. Their natural foraging behaviors have them continuously picking at leaves and sifting through plant material for food. This helps suppress duckweed growth and satisfies their need to graze. Cichlids do best with plenty of open swimming space.
Gouramis are anabantoid labyrinth fish that breathe oxygen from the surface, so they spend much time near floating duckweed. Dwarf gouramis, honey gouramis, and pearl gouramis will all nibble away at duckweed. Their inquisitive nature and plant-based diets make them ideal for duckweed control. Just watch for aggression with male gouramis.
Betta fish thrive among dense thickets of plants, so floating duckweed appeals to their instincts. They pick at duckweed when hunting for snacks on the surface and nest among the leaves. The shade it provides helps shy away from tankmates. Male bettas may become territorial during breeding times. Ensure plenty of open areas between plant groupings.
These livebearers are mainly herbivorous, feeding on algae and plant matter. Mollies (sailfin, Dalmatian, black) spend much time picking duckweed off the surface. Their energetic feeding makes them excellent duckweed management fish. Just watch for aggressive behavior between males.
Schooling tetras like neons, rummy noses, and bleeding hearts will graze on duckweed, especially when kept in larger groups. They may not eat as much as primary plant eaters, but their numbers increase. Tetras bring movement and activity to the upper levels where duckweed grows. Avoid fin-nipping species like Serpae tetras.
Many barbs are opportunistic omnivores that will snack on duckweed. Tiger, cherry, and rosy barbs actively forage across all tank levels. Their adventurous appetites and schooling nature ensure they cover plenty of ground eating duckweed. Just be cautious with notoriously nippy species.
While not surface feeders, plecos will rasp duckweed off hard surfaces like driftwood and aquarium walls. Common plecos grow quite large, so consider a smaller species like clown or bristlenose. They clean up sinking duckweed that reaches the bottom. Their suckermouths work nonstop.
Bottom-dwelling loaches like clown and yo-yo loaches will consume any duckweed that sinks to their level. They use their down-turned mouths to pick food from the substrate. Loaches are energetic and engage in intriguing behaviors. However, many get too large for standard aquariums when mature.
An African cichlid species, tilapia fish relish duckweed and are sometimes used for duckweed control in ponds. They have a varied diet but particularly enjoy grazing on aquatic vegetation. However, tilapia are invasive and illegal in some areas, so research regulations before introducing them.
Small freshwater minnows are capable of putting a dent in duckweed populations. Fathead minnows, white cloud minnows, and rosy red minnows will all graze on floating duckweed. They need to be kept in schools to maximize their duckweed consumption. Minnows prefer cooler water temperatures.
Other Creatures That Eat Duckweed
While fish are the primary consumers of duckweed in aquariums and ponds, other creatures will eat it as well:
- Shrimp like amanos, ghost, and bamboo pick at duckweed.
- Snails like mystery, rabbit, and nerite scrape duckweed off surfaces.
- Aquatic frogs like African dwarf and African clawed frogs will eat duckweed.
- Larvae of mosquitoes, mayflies, and dragonflies consume duckweed.
- Ducks, geese, and swans eat duckweed in ponds.
So in addition to fish, invertebrates, amphibians, insects, and waterfowl will all feed on duckweed to some degree. An ecosystem with diverse organisms helps keep duckweed balanced through combined feeding efforts.
Managing Duckweed Growth
While introducing duckweed-eating species can control growth, you typically need multiple additional strategies to find the right equilibrium. Useful tactics include:
Removing Excess Duckweed
Removing excess duckweed by hand or using a net is usually necessary, even with plant-eating fish. Take out large portions weekly or whenever it covers over 50% of the water’s surface. Use an aquarium vacuum on the substrate to suck up any that sank. Consistent removal helps reset the balance.
Too much light fuels explosive duckweed growth. Use floating plants like water lettuce to create shade, position tall plants strategically, or reduce your light intensity and duration. 8-10 hours daily with moderate lighting suited to your tank size is a good baseline to aim for.
Duckweed thrives on excess nutrients like nitrogen and phosphates. Reduce feeding amounts, avoid overstocking, siphon the substrate, and perform water changes to lower nutrients. Adding floating plants and fast-growing stem plants helps use up nutrients before the duckweed can utilize them.
Introducing Duckweed-Eating Species
As covered earlier, certain fish, invertebrates, and other species will eat duckweed. Start with a clean slate by removing all duckweed, then add a combination of duckweed consumers to help control regrowth. Monitor growth and adjust as needed.
What fish eat duckweed?
Goldfish, koi, catfish, cichlids, bettas, gouramis, mollies, tetras, barbs, plecos, loaches, tilapia, and minnows are examples of fish that will eat duckweed.
How do I get rid of too much duckweed?
Manually removing duckweed, reducing light intensity, controlling nutrients, and adding duckweed-eating species will help control an overgrowth. Combining several methods is the most effective.
Will duckweed harm my fish?
In small amounts, duckweed benefits aquariums. But if left unchecked, excessive duckweed can reduce oxygen, block out light, and deteriorate water quality, harming fish health.
What should I do if my filter gets clogged with duckweed?
Clean out the intake strainer and any blocked parts of the filter. Performing more frequent maintenance and surface skimming helps prevent excessive buildup. Adding a pre-filter sponge provides additional protection.
Is duckweed good for fry and small fish?
The shelter and cover duckweed can benefit fry and small species. But monitor growth levels to prevent oxygen deficiencies. Leaving open areas allows proper gas exchange.
Duckweed can be either a blessing or a curse in home aquariums. Maintaining the right balance allows you to take advantage of its benefits without the drawbacks of unchecked growth. Fortunately, introducing fish that eat duckweed is an organic way to regulate its spread. Proper management allows your tank to grow healthy duckweed and happy fish.