The best foods for herbivorous fish – a complete guide

Feeding herbivorous fish in freshwater and marine aquariums is most often based on ready-made foods containing spirulina. This microalga has become the cornerstone of aquarium diets thanks to its unique nutritional profile and health-promoting properties. But spirulina is not the only option. Many other algae and vegetables can also play an important role in the diet of aquarium fish.

In this guide, you’ll learn about the best foods for herbivorous fish and how to diversify their diet to ensure healthy growth, proper nutrition, and natural support for their bodies.

Why is a plant-based diet important for aquarium fish?

Plant-based foods are the foundation of a herbivorous fish’s diet and a vital part of the diet of omnivorous species, which make up the majority of fish kept by aquarists. Herbivorous fish require foods that match their specific nutritional needs, as their bodies are designed to process plants.

Their long digestive tracts allow them to extract maximum value from plant matter, while their specialized mouthparts, often equipped with unique teeth, enable them to feed on higher plants and graze effectively on algae growing on rocks, branches, logs, and aquatic vegetation.

Spirulina and Chlorella – superfoods for herbivorous fish

As mentioned earlier, spirulina is the most common ingredient in aquarium fish foods, typically making up anywhere from a few to several dozen percent of the formula. Its properties are well known to aquarists, unlike some other algae such as Chlorella, Scenedesmus, Laminaria, Ascophyllum, Undaria, or Ulva, which are more common in feed for farmed fish than ornamental species. You can read more about spirulina in the article: Spirulina – super algae for aquarium fish.

Here, however, we’ll focus on chlorella – the second most commonly used alga in aquarium foods.

Why add chlorella to the diet of aquarium fish?

Chlorella vulgaris is a single-celled green alga (Chlorophyta) found in both fresh water and moist habitats. Interest in chlorella, much like spirulina, originally came from its potential use as a protein source for humans and farm animals. In its dry form, chlorella contains 45–57% protein rich in essential amino acids. It is also a valuable source of provitamin A, folic acid, and iron, making it an excellent additive in ready-made fish foods. But that’s just the beginning.

Chlorella is prized for its health benefits, largely due to the presence of beta-glucan, a natural immunostimulant, and its high chlorophyll content (around 2% of dry matter). Beta-glucan strengthens both specific and non-specific immunity, helping fish build a stronger natural defense system. Chlorophyll improves digestion, inhibits the growth of harmful bacteria in the gut, acts as an antioxidant, and supports detoxification. Observations also suggest that, when used in baths, chlorella can accelerate wound healing and help combat skin infections. In addition, chlorella supports cell regeneration and raises hemoglobin levels in the blood.

Like spirulina, it is also an excellent source of carotenoids – around 0.4% of its dry mass, with 80% of these being red pigments. This high concentration of carotenoids helps enhance fish coloration. You can read more about carotenoids and color-enhancing foods in these articles:

• Color-enhancing foods for fish – how do they work?
• How do carotenoids affect the coloration of fish?

And that’s not all – chlorella also improves fat metabolism and helps prevent fatty degeneration of internal organs.

Kelp Algae – a source of minerals for aquarium fish

“Kelp algae” is a trade name for several species of brown algae. Tropical uses Ascophyllum nodosum and Laminaria digitata in many of its foods. Their biggest advantage is their very high content of minerals such as iodine, iron, potassium, magnesium, calcium, selenium, and phosphorus present in easily digestible organic forms. Kelp also provides vitamins (A, B1, B2, B3, B9, C, and E) and natural pigments like chlorophyll and fucoxanthin (a carotenoid).

But what really sets kelp apart is its high fiber content, making up 33–50% of its dry weight – much more than higher plants. This fiber is divided into insoluble fractions (cellulose, mannan, xylan) and soluble fractions (alginic acid, fucoidan, laminarin). Fiber plays a vital role in:

• slowing intestinal transit time,
• promoting beneficial gut microflora,
• binding bacterial toxins and heavy metals,
• improving food absorption, which translates into better growth,
• detoxifying the body.

Studies also confirm that alginic acid, fucoidan, and laminarin have antibacterial and antiviral effects, while boosting immunity in fish. You can find kelp algae in Tropical Green Algae Wafers.

Vegetables and fruits in the diet of herbivorous fish

Herbs, vegetables and fruits can also enrich the diet of herbivorous fish. Herbivorous Loricariidae fish, for example, eagerly eat cucumber and zucchini. Just be sure to source vegetables from reliable suppliers to avoid pesticide contamination. Silverdollars are even known to enjoy watermelon, and many species relish fresh or dried nettles.

Food producers also incorporate vegetables, fruits, and herbs into their formulas. Tropical, for instance, adds ingredients such as:

• nettles,
• spinach,
• young alfalfa shoots,
• green peas,
• wheat germ,
• ketapang leaves,
• aloe extract,
• fruits,
• grasses,
• oak bark meal.

These provide plant protein, fiber, vitamins, and minerals, creating a balanced diet for herbivorous and omnivorous fish alike.

It’s worth noting that ready-made herbivorous fish foods are not 100% plant-based. Why? Because in the wild, herbivores also consume small invertebrates. That’s why high-quality foods include fish, crustaceans, molluscs, or even insects to ensure a truly balanced diet.

How to choose the best plant-based food for aquarium fish

While spirulina remains the most popular choice for herbivorous and omnivorous fish, it’s not the only valuable option. Chlorella is just as nutritious, and kelp algae supply essential minerals and fiber that support digestion and overall health. Tropical also enriches its foods with vegetables, herbs, and fruits, ensuring variety and a wide range of nutrients.

When choosing a food, consider not only its ingredients but also its form. The right format depends on the size of your fish and where they feed in the aquarium. Flakes are the most versatile option, they can be crumbled if needed and spread evenly through the water, making them ideal for multi-species tanks where shy or subordinate fish need equal access to food.

What to feed cichlids from Lake Malawi?

Cichlids thrive on plant-based granulated foods, making them a great choice for herbivorous species from Lake Malawi. Depending on the type of cichlids you keep, you can combine Tropical Soft Line Africa Herbivore with Tropical Super Spirulina Forte Granules and Tropical 3-Algae Granulat.

For species that require more animal protein, opt for Tropical Malawi or Tropical Krill Gran with krill.

Another interesting option is Tropical Gel Formula for Herbivorous Fish – a DIY jelly food containing five types of algae (36% of its composition). This unique formula creates a natural feeding ground for cichlids and catfish. You can read more about it here: Soft Gel food for fish.

What to feed algae eaters?

For so-called “algae eaters” – usually catfish from the Loricariidae family – tablets and wafers are the best choice. Keep in mind, though, that not all catfish are algae eaters. If you have an algae-eater in your tank read Common Bristlenose Catfish (Ancistrus sp.).

For more on choosing the right food form, see: How to choose food for fish.

Tropical ready-made plant foods for fish

You already know which ingredients to look for in vegetable foods and how important their form is. Here’s a selection of Tropical foods with algae and vegetables that help create a varied diet for herbivorous and omnivorous fish:

• Tropical Super Spirulina Forte – a classic spirulina-based food for herbivorous and omnivorous fish (36%) that supports health, digestion, and color intensity. Available in several forms to suit different species.
• Tropical 3-Algae – enriched with sea algae, chlorella, and aloe extract, ideal for diversifying diets of herbivorous and omnivorous fish.
• Tropical Gel Formula for Herbivorous Fish – DIY jelly food with five algae species (36% composition), creating natural feeding grounds.
• Tropical Soft Line Africa Herbivore – soft granules for African herbivorous fish, perfect for Lake Malawi cichlids from the mbuna group.
• Tropical Green Algae Wafers – sinking wafers for bottom feeders like catfish, with added algae and ketapang leaves.
• Tropical Hi-Algae Discs – sinking discs rich in algae (52.4%) for herbivorous bottom-feeders and shrimp.
• Tropical Pleco’s Tablets – large, breakable spirulina tablets for catfish.
• Tropical Spirulina Flakes / Granulat – basic spirulina foods for ornamental fish, supporting digestion.
• Tropical Micro-vit Vegetable – powdered food for fry with nettle and spinach.
• Tropical Micro-vit Spirulina – powdered fry food with spirulina.

Common mistakes in feeding herbivorous fish

• Wrong diet for the species – Avoid giving herbivores foods dominated by animal ingredients. This can cause digestive problems, intestinal inflammation, and even death.
• Overfeeding – Too much food leads to fatty degeneration of internal organs, weakened immunity, and reproductive issues.
• Sudden diet changes – Introduce new foods gradually by mixing them with your fish’s current diet.
• Poor variety – Offer different foods to provide a balanced and diverse diet.
• Unsafe fresh vegetables – Only feed vegetables from trusted sources. Those treated with pesticides can poison your fish.

Literature

• Dawczynski, Ch., Schubert, R., Jahreis, G., (2006). Amino acids, fatty acids, and dietary fibre in edible seaweed products. Food Chemistry 103, 891-899.
• Gholam, R. Nematipour, Nakagawa H., (1988). Effects of Dietary Lipid Level and Chlorella-extract on Ayu, Nippon Suisan Gakkaishi 54(8), 1395-1400.
• Kraan, S. (2012). Algal Polysaccharides, Novel Applications and Outlook, in Carbohydrates ‒ Comprehensive Studies on Glycobiology and Glycotechnology, Chuan-Fa Chang (Ed.), ISBN: 978-953-51-0864-1, InTech, DOI: 10.5772/51572.
• Nakagawa H., (1997). Effect of dietary algae on improvement of lipid metabolism in fish, Biomed & Pharmacother, 51, 345-348.
• Tartiel, M. Badwy, Ibrahim, E. M., Zeinhom, M., (2208). Partial replacement of fish meal with dried microalga (Chlorella spp and Scenedesmus spp) in Nile tilapia (Oreochromis Niloticus) diets, 8th International Symposium on Tilapia in Aquaculture.
• Zahira, Y., Ehsan, A., Afifi, Z., Masita, M., Mohd, S.T., (2014). An overviev: biomolecules from microalgae for animal feed and aquaculture, Journal of Biological Research, 21:6.

• Author
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Dr. Aleksandra Kwaśniak-Płacheta

Hydrobiologist and aquarium expert, with a special focus on ornamental fish nutrition. She has published numerous articles in magazines such as Nasze Akwarium, Magazyn Akwarium, Tanganika, and Aquafeed Magazine. An experienced trainer and speaker, she has shared her expertise at aquarium symposia and, for many years, led the Wrocław Aquarium Society.

She studied environmental protection (specializing in surface water protection) at the Agricultural University of Wrocław (now the University of Life Sciences), where she later obtained her PhD at the Faculty of Biology and Animal Husbandry.
Her research focuses on the effects of diet, supplementation, and natural additives on the health, condition, and reproduction of aquarium fish.

In her free time, she cares for her fish and cats, tends to plants, enjoys hiking, and stays active through sports.

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