The Complete Guide to Live Foods for Fry: From Infusoria to Microworms

If you’ve ever raised a batch of tiny fry only to watch them fade away one by one, you’ll know that feeding them right from day one is half the battle.

The problem isn’t enthusiasm — it’s size. Most baby fish are far too small to take crushed flake or powdered foods, and that’s where live foods come to the rescue.

They’re the difference between fry that merely survive, and fry that grow fast, healthy, and vibrant.

I learned this the hard way. My first guppy fry looked like they were doing great — darting about, nibbling at whatever floated past — until a week later when half had disappeared. I

t wasn’t poor water quality; they were simply starving, unable to eat the food I thought was “small enough”. Once I discovered live foods like vinegar eels and microworms, everything changed.

Why Live Foods Are Essential for Fry

Fry need food that moves, fits in their mouths, and stays suspended in the water column long enough for them to catch it. Live foods tick every box.

They’re rich in natural proteins and fats, stimulate a hunting response, and — unlike most dried foods — they don’t foul the water instantly.

Each species has its own niche in the fry-raising journey, and knowing when to use which is the real trick.

Think of it as a ladder. At the very bottom, we start with infusoria — microscopic life that even the tiniest newborn tetras or gouramis can manage.

As the fry grow, we move them up to slightly larger options like vinegar eels, banana worms, and microworms.

By the time they’re ready for brine shrimp nauplii or crushed pellets, they’re strong, healthy little fish with well-developed digestive systems.

Stage 1: Infusoria — The First Food

Infusoria is a catch-all term for the microscopic life that grows in any bit of decaying plant matter. Paramecia, euglena, rotifers — all the things you normally can’t see, but your fry can.

You can make a simple culture at home by soaking a piece of lettuce or banana peel in tank water for a few days, keeping it warm and light. Within a few days, you’ll see the water go slightly cloudy — that’s the bloom.

It doesn’t smell great, but it works. A few drops of this cloudy water into your fry tank every day gives your tiniest fish a steady supply of live prey. You can learn more about setting up a reliable culture in our Infusoria guide.

Stage 2: Vinegar Eels — Surface Dwellers for the Next Stage

Once your fry have doubled in size — usually around 5–7 days in — they’re ready for their next step up: vinegar eels.

Despite the name, they’re harmless nematodes that thrive in apple cider vinegar and swim right up near the water’s surface. That’s perfect for fry that like to feed high in the water column, such as bettas, gouramis, and guppies.

The best part? Vinegar eel cultures are practically maintenance-free. Feed your fry by drawing a small amount of eels from the top and rinsing them into the tank.

They can live in freshwater for a day or two — long enough for even the slowest fry to get their fill. We sell starter cultures ready to go on the ShrimpKeeper store if you’d like to try them.

Stage 3: Banana Worms, Microworms, and Walter Worms — The Growers

As your fry continue to grow, they’ll quickly outgrow vinegar eels. This is where the “micro” worms come in — banana worms, microworms, and Walter worms.

Despite their name, these aren’t worms at all but tiny nematodes that live on porridge-like cultures made from oats or mashed potato. They’re a staple for breeders everywhere.

Banana Worms

Banana worms are the smallest of the trio, perfect for the early transition from vinegar eels. They’re slightly shorter and thinner than microworms, and fry such as bettas, danios, and smaller livebearers take to them straight away.

They move slower than vinegar eels, which means they stay in reach of fry a bit longer.

Microworms

Microworms are the gold standard of fry foods — a little larger than banana worms and packed with protein.

They form a wriggling film on the sides of their culture container, ready to be wiped off and fed. Fry that have been feeding for a week or more on vinegar eels will usually switch to microworms effortlessly. They’re ideal for guppies, rainbows, and cichlid fry.

Walter Worms

Walter worms sit right between microworms and baby brine shrimp in size, making them an excellent bridge food.

They’re slightly more active and stay suspended longer, which encourages natural foraging behaviour. Once your fry can comfortably eat these, you’re ready for the final jump to brine shrimp or powdered dry foods.

Stage 4: Baby Brine Shrimp — The Protein Powerhouse

No live food list is complete without mentioning baby brine shrimp.

They’re not part of the “micro” culture family, but they’re the classic final step before fry move to prepared foods. Freshly hatched brine shrimp nauplii are packed with protein, fat, and natural carotenoids that enhance colour.

They swim in short, jerky motions that fry can’t resist. Once your fish reach this stage, growth becomes explosive.

How to Use Live Foods Safely

Live foods are brilliant, but they do need a little care. Never overfeed — uneaten worms or infusoria will decompose just like uneaten flakes.

Start with small, frequent feedings and siphon out debris daily. I like to alternate live feeds with a powdered fry food, which helps balance nutrition while giving the fry some variety.

Keep separate cultures for each live food type, and always wash your hands or tools between them to prevent cross-contamination.

Each species thrives best under slightly different conditions — vinegar eels in acidic vinegar, microworms in a moist medium — so keep them apart and labelled.

My Routine: The “Fry Ladder” in Action

Here’s how I usually run things in my fish room:

• Days 1–5: Infusoria (twice a day)
• Days 5–10: Vinegar eels (morning), banana worms (evening)
• Days 10–20: Microworms and Walter worms, gradually introducing baby brine shrimp
• Day 20 onward: Transition to crushed flake or powdered food

By following this simple progression, I’ve raised hundreds of healthy fry across different species — from guppies to rainbowfish.

It’s predictable, reliable, and once your cultures are established, it costs next to nothing to maintain.

Setting Up Your Live Food Station

If you’re serious about breeding fish, a small live food “station” is worth its weight in gold. I keep mine on a warm shelf in the fish room — five small plastic tubs with lids, each labelled and dated.

A quick stir or wipe every morning, and I’ve got all the food I need. Cultures last for months if you refresh them occasionally with fresh oats or apple cider vinegar.

It’s one of those setups that seems over the top until you’ve tried it — and then you wonder how you ever managed without it.

Once your fry are thriving and you can see the difference in growth and colour, you’ll never go back to powders alone.

Final Thoughts

Raising fry is one of the most rewarding parts of the hobby — and live foods make it ten times easier. They’re natural, nutritious, and endlessly fascinating to watch under a magnifying glass.

Start small, build your “ladder”, and before long you’ll have jars of wriggling life ready to feed every batch that comes along.

If you’re ready to begin, start with a simple vinegar eel culture or a microworm culture. Once you see your fry thriving on live foods, you’ll understand why every successful breeder swears by them.