Do Fish Eat Seaweed?

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For many types of fish, YES seaweed provides a meal as well as a place to live in. While there are carnivore fish that eat only meat, omnivorous and herbivorous species will eat nori or kelp and other types of seaweed. 

A majority of a fish’s time is spent looking for something to eat, and since they live entirely in water, their diet is limited to what can be found in that environment. Some omnivorous species eat more seaweed as opposed to other smaller fish, shrimp, or aquatic critters. 

Many freshwater fish types are primary herbivores. By reading on, you’ll be able to know if you can feed your aquarium fish with seaweed. 

In essence, you’ll identify the best seaweed for your fish tank, differentiating between what is decoration and what is food.

Which Underwater Plant Material is Seaweed?

There are many plants living alongside the fish in the water, existing near the sunlit surfaces of oceans, lakes, and rivers. These plants, collectively known as seaweed, can be free-floating, drifting within the water, or having roots attached to a water body’s bottom.

Where seaweed is, you’ll find a variety of fish that eat seaweed and those that eat the organisms that live within it. Seaweed is used as a hiding place for smaller fish against larger predators prowling nearby.

Other types of seaweed, such as seagrass, are flowering plants and produce a lot of oxygen, which fish benefit from.

With 52 different species, sea grassroots at the bottom and pervade protection for small aquatic fish and critters. Types of seagrass include star grass, paddle grass, turtle grass, Johnson’s seagrass, and manatee grass.

Thongweed is also as common as kelp, a seaweed form with strap-like leaves and mushroom-shaped buttons. These plants are olive green in color and live underwater for approximately three years.  

What Kind of Fish Eat Seaweed?

Depending on their natural habitats, like the depth at which they swim,  fish obtain nutrition from seaweed or underwater vegetation. Whether saltwater or freshwater species, there is a wide variety of aquatic plants and algae that fish will feed on. 

Fish that eat seaweed need to feed regularly to assimilate nutrients properly and have a more extended digestive system. Plant-based foods need a slower and more complicated digestion process in comparison to meat or other fish eaters.

The amount of seaweed fish will eat depends on their digestive systems’ ability to obtain as much nutrient content as possible.

Tropical fish, for instance, have a well-evolved digestive system for aquatic bases plant vegetation. Seaweed offers anti-inflammatory benefits and improves the immune systems of salt or freshwater, marine, and tropical fish.

Which Freshwater Fish Eat Seaweed?

Having fish that eat live seaweed in your aquarium helps control its wild growth, keeping the tank clean and colorful. Seaweed is also readily available as freshwater fish food, and it gives fish a robust constitution.

Some fish species that eat seaweed and which I recommend for keeping in your aquariums include;

Black Molly Fish

This is also known as black Melanesia, one of the more decorative tropical fish species for your aquarium. Black molly fish can grow up to four inches long with a fusiform and elongated body.

These seaweed-eating fish present an opaque black coloration, and in some cases, males have an upper dorsal fin orange or reddish border.

Black molly fish keep the aquarium clean, especially when other fish are adapting to a growing ecosystem. I would recommend not feeding black molly fish for about a month in a new aquarium so that they eat the seaweed when it starts to grow. 

Plecostomus Fish

The characteristically ventrally flattened Plecostomus fish feature bony plates that cover their bodies. They can grow to between 11 and 20 inches long and have a suction cup-like mouth.  

Smaller Plecostomus fish are more suited to aquariums, as the larger they get, the more seaweed and other vegetation they’ll require.  

These fish require space, preferably in tanks with over 53 gallons of water. Plecostomus fish can live up to 15 years in your aquarium, but the substrate in the tank should be thick so as not to be dragged by these boisterous swimmers. 

Otocinclus Fish

Another suckered mouth fish and the smallest loricariid fish, Otocinclus, have a spindle-shaped body and flat belly. These fish have a lateral vision, an adipose fin and can grow to measure up to 2 inches long. 

Otocinclus fish must be acquired in groups as they are naturally schooling fish. However, veterinarians warn that apart from eating seaweed, these fish also target other species’ viscous layers, which can create inter-tank conflicts.  

Siamese Fox Fish

The Siamese fox fish has completely colorless fins and prefers slightly acidic but soft water. Siamese fox and their counterparts, the flying fox, are much preferred, and they eat seaweed, especially the red variety.

Give Siamese fox fish enough oxygen supply in the tank. If you have their flying fox flying cousins, it’s advisable to keep the tank closed as they can leave the aquarium. 

Farlowella Fish

This is a weird shaped fish known as the rod, pen, and catfish, amongst others. A gregarious fish, the Farlowella is peaceful and quiet, feeding on seaweed and other vegetables. 

These fish can reach up to seven inches long and, as such, need a spacious aquarium with no less than 26 gallons of water. Farlowella fish are not timid, preferring an ecosystem with logs and plants where they are a big attraction. 

Which Saltwater Non-Aquarium Fish Eat Seaweed?

Other than these aquarium fish, wild varieties can’t be kept but also eat seaweed. These include;

The Crescent Fish

This fish is also known as blue perch or blue bass due to its upper side coloration. Crescent fish prefer shallow waters and can be found near banks of seaweed. 

Opal Eye Fish

The Opal’s eye is an omnivore fish that feeds and lives near seaweed beds, often in shallow waters. This fish has an almost square tail fin, and except for two whitish-yellow spots beneath its dorsal fin, it’s dark green.

Pacific Blue Tang

These fish are also called tang palette, surgeonfish, real tang, or hippopotamus fish. The pacific blue tang is omnivorous, meaning seaweed and plankton; they also hunt small insects that fly near or fall on the water’s surface.  

Also Read: Can Octopus Breathe Air?

How to Feed Your Fish Seaweed

When you have seaweed eaters for fish, you can’t leave them to only graze on the available foliage within your aquarium. Fish that eat seaweed, particularly the strict herbivore types, need to consume more food than those which rely on meaty fare.

You have to supplement the seaweed uptake of your herbivore or omnivore fish for normal metabolism and growth.

You have the option of selecting prepared or live seaweed diets, which can be dried whole or pelleted into small sizes. Live seaweed is preferable and lush patches of kelp or nori will provide your fish with the nutrition they need. 

If your seaweed comes in sheets, you can tear off pieces and throw into the tank or attach it to a feeding clip in rolls. You can also tie kelp or nori pieces to the decorations in your aquarium, taking care not to obstruct water pumps or filters.

Is Dried Seaweed okay to Feed Fish?

Dried seaweed, such as nori or kelp, is good to feed your fish with. Most of these varieties are readily available as dried fish food, either in their original form or as flakes. 

The health benefits of raw seaweed are still preserved in the dry variety, including being high in vitamins, minerals, proteins, and carbohydrates.

You can tear off dried seaweed pieces and hold them in the aquarium water to hydrate while rubbing it with your fingers. Once it’s softened up enough, release it and let it float to attract your fish’s attention.

Use various seaweed types such as Kombu, which can be purchased dried from Asian grocery stores seeing as it’s a human delicacy. For dried nori, you’ll find two varieties of the red or the purple, also common as it’s used in sushi making.

Dried seaweed is ideal for feeding angelfish, surgeonfish, celeste fish, and others. 

Frequently Asked Questions 

Do Shrimp Eat Seaweed?

A wide variety of shrimp makes great excellent aquarium pets, both for fresh and saltwater tanks. Shrimp are the guardians of the aquarium, helping to keep it clean by eating filamentous algae.

Although they feed on other seaweed types, their favorite is Riccia fluitans, a moss-like plant known as Riccia.

Do Snails Eat Seaweed?

Yes, Snails do feed and live in seaweed, but they prefer microscopic plankton to algae. 

Do Fish Eat Plants?

Yes, the same fish that eat seaweed will eat other types of vegetables, including lettuce, broccoli, carrots, and peas. As long as the material is easily chewable, you can structure a plant diet that supplements your seaweed eating fish. 


As an aquarist or fish owner, you should feed fish live or dried seaweed to complement the diet of your omnivorous or herbivorous keeps. Introduce your fish to kelp, nori, or Kombu, alongside other plant vegetables, and they’ll soon be nibbling enthusiastically. 

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