How to Feed Vegetarian Marine Fish

In this guide

A surprising number of the most popular reef fish, tangs, surgeonfish, rabbitfish and several angelfish, are herbivores or near-herbivores in the wild, spending most of their day grazing algae off rock and coral rubble. Feeding them a diet built around meaty frozen foods, the default in many mixed reef tanks, is one of the more common and avoidable nutrition mistakes in the hobby.

Fish that need a plant-heavy diet

• Tangs and surgeonfish (yellow tang, kole tang, sailfin tang and others), among the most committed herbivores in the hobby
• Rabbitfish, similarly algae-focused grazers
• Certain angelfish, particularly the larger marine angelfish species, which need substantial algae content alongside sponge matter
• Blennies such as the lawnmower blenny, which strip algae film off rock and glass

What to actually feed them

• Dried nori (unseasoned sushi seaweed), clipped to the tank wall with a magnetic feeder or veggie clip so fish can graze at will
• Spirulina and marine algae based flakes or pellets as a daily staple
• A rotating mix of nori, ulva (sea lettuce) and other dried macroalgae for variety, rather than nori alone
• Occasional meaty foods (mysis, krill) in smaller amounts, since even committed herbivores benefit from some protein

Why this matters beyond just growth

Chronic under-feeding of algae in these species is directly linked to head and lateral line erosion (HLLE), covered elsewhere in this series, along with poor colour, weakened immune response and stunted growth. Tangs kept without adequate algae are also more prone to picking at coral or ripping at other tank decor out of sheer dietary frustration.

Getting a reluctant fish to eat nori

Newly introduced tangs sometimes don't recognise nori as food at first. Clipping it in the tank and leaving it for a day or two, letting it soften and drift slightly, usually gets them investigating out of curiosity, and once one fish in the tank learns to eat it, others tend to follow quickly. Persistence over the first week or two is usually all that's needed.

A note on live rock and grazing

A tank with a healthy, established covering of coralline and film algae on the rockwork gives herbivorous fish something to graze on between feedings, closer to their natural pattern of near-constant small bites rather than two large meals a day. This isn't a substitute for supplemental feeding, but it meaningfully rounds out the diet.

Sourcing nori in India

Plain, unseasoned sushi nori is increasingly easy to find in India through general grocery delivery apps and supermarkets catering to Japanese and Korean cuisine, and this works out considerably cheaper than nori sold specifically as aquarium food. The only thing to check is the ingredient list: some sushi nori sold for eating is lightly oiled or salted, and that variant should be avoided in favour of the plain, unseasoned sheets.

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