Microworms — The Complete Culture & Feeding Guide
Microworms are one of the most effective, accessible and reliable live foods available to UK aquarium keepers — yet most hobbyists have never used them. This guide covers everything you need to know.
What Are Microworms?
Microworms (Panagrellus redivivus) are free-living nematodes — microscopic, non-parasitic roundworms that measure approximately 1–2mm in length. Despite being commonly called worms they are not true worms at all, but a separate phylum of organism entirely distinct from earthworms, grindal worms or white worms.
They are completely harmless to humans, fish and aquatic invertebrates. They cannot infest your tank, cannot parasitise your livestock and will not survive in aquarium water for more than 8–12 hours — making them one of the safest and most controllable live foods available.
Key FactMicroworms are not classified as animals under the Animal Sentience Act 2022 (England and Wales). They are nematodes — a biologically distinct category from vertebrates, crustaceans and molluscs. They have no known sentience and are widely used in aquaculture globally.
At a Glance
Why Use Microworms?
Live food triggers feeding responses in fish that prepared foods cannot replicate. The wriggling motion of microworms in the water column stimulates instinctive predatory behaviour — particularly important for fish fry that have recently absorbed their yolk sac and are beginning to feed independently.
Nutritional Profile
Microworms are rich in protein and fat — making them an ideal growth food for developing fry. Their small size means even the tiniest mouth can consume them without difficulty, and their soft body structure means they are easy to digest compared to larger live foods.
Size Advantage Over Other Live Foods
Microworms
- 1–2mm — ideal for tiny fry
- Wriggling motion in water
- Survive 8–12 hours in tank
- Easy to culture at home
- No saltwater required
- Available year round
- Cost effective per feeding
Baby Brine Shrimp
- Larger — unsuitable for smallest fry
- Requires saltwater hatch setup
- 24hr hatch time per batch
- More equipment intensive
- Must be rinsed before feeding
- More wastage if overfed
- Higher ongoing cost
ImportantFor the very smallest fry — bettas, killifish, neon tetras, guppies — microworms are often the only live food small enough at first feeding. Baby brine shrimp can be too large for newly hatched fry of these species during their first days of independent feeding.
Which Fish Benefit Most
Betta Fry
Microworms are the gold standard first food for betta fry. Their size and wriggling motion make them ideal for newly free-swimming bettas transitioning from infusoria.
Killifish
Killifish fry are often extremely small. Microworms are frequently the only live food small enough for newly hatched annual killifish to consume successfully.
Guppies & Livebearers
Livebearer fry are larger but microworms provide excellent nutritional variety alongside dry foods, supporting rapid early growth.
Corydoras & Catfish
Bottom dwelling species benefit from microworms sinking to the substrate. Their wriggling motion attracts even the most reluctant feeders.
Neon & Cardinal Tetras
Tetra fry are notoriously difficult to feed. Microworms are consistently one of the most successful first foods for newly free-swimming neon and cardinal tetra fry.
Angelfish & Cichlid Fry
Cichlid fry benefit significantly from live food in their first weeks. Microworms supplement dry foods and support the growth rates cichlid keepers expect.
Nano Fish
Adult nano species — chilli rasboras, celestial pearl danios, dwarf puffers — take microworms readily as a regular part of a varied feeding programme.
Axolotls (Juveniles)
Juvenile axolotls can be fed microworms as a supplementary live food during their early developmental stages.
Getting Started With Your Culture
Jack's Aquatics Microworm cultures are supplied in an active 2oz pot on a ready-prepared substrate — your culture is already producing worms and ready to harvest within 24–48 hours of arrival. No setup is required to begin feeding immediately.
If you want to extend and expand your culture — which we recommend for consistent long term supply — follow the steps below.
What You Need
- Your Jack's Aquatics starter culture (2oz pot)
- 2–3 small plastic containers with lids (deli containers work well)
- Instant mashed potato or plain rolled oats
- Baker's yeast (small pinch)
- Clean water (dechlorinated or cooled boiled)
- Cotton bud or small spatula for harvesting
Preparing Your Substrate
Mix instant mashed potato with water to form a thick, moist paste — similar to the consistency of set porridge. Spread approximately 1–1.5cm deep in the base of your container. The substrate should be moist but not wet — if water pools on the surface it is too wet and the culture will fail.
Sprinkle a tiny pinch of baker's yeast across the surface. The yeast feeds the microworms and keeps the culture active.
TipUse instant mashed potato over oats where possible — it produces less odour, lasts longer and maintains a more stable culture environment. Rolled oats work but tend to become sour more quickly.
Seeding Your New Culture
Take a small portion of your Jack's Aquatics starter culture — approximately a teaspoon — and spread it across the surface of your prepared substrate. Replace the lid slightly ajar to allow air circulation while preventing contamination. A few small holes in the lid work well.
Within 2–3 days you will see the characteristic shimmering film of microworms climbing the walls of your container. This is your cue that the culture is established and productive.
Temperature, Placement & Care
| Condition | Ideal | Notes |
|---|---|---|
| Temperature | 20–25°C | Higher temps speed production but shorten culture life |
| Location | Warm, dark spot | Avoid direct sunlight and temperature fluctuation |
| Airflow | Slightly ajar lid | Culture needs air but not exposed — prevents drying and contamination |
| Humidity | Moist substrate | If substrate dries, add a few drops of dechlorinated water |
| Culture lifespan | 3–4 weeks | Restart on fresh substrate before productivity drops |
WarningAlways run two or three cultures simultaneously at different stages. If a single culture crashes you have no backup. Stagger your new culture starts by 1–2 weeks so you always have a productive culture available.
Harvesting and Feeding
Once your culture is established microworms climb the walls of the container in a visible, moving film. This is the cleanest and most efficient point to harvest.
The Wall Scrape Method
- Look for the cloudy moving film of worms on the container walls
- Use a clean cotton bud, small spatula or your fingertip to wipe a small amount off the wall
- Swirl in a small cup of aquarium water to rinse away any substrate residue
- Use a pipette or syringe to deliver directly to your fry tank or feeding zone
- Feed small amounts multiple times per day rather than one large feed
Key PointNever add substrate directly to your tank. Always harvest from the walls and rinse in aquarium water first. Uneaten substrate in a tank will decompose rapidly and spike ammonia.
How Much to Feed
Microworms survive 8–12 hours in freshwater — any uneaten after this time will die and begin to decompose. Feed only what your fish can consume within a few hours and observe your fish's response. If worms remain after several hours reduce the amount at the next feeding.
Troubleshooting Your Culture
Strong Sour Smell
Normal in small amounts. Very strong vinegar or alcohol smell indicates the culture is acidifying and nearing the end of its productive life. Start a fresh culture immediately.
No Worms on Walls
Culture may be too cold or too wet. Check temperature is above 20°C and that substrate is moist not waterlogged. Give it 24–48 hours after adjusting.
Mould Appearing
Small amounts of surface mould are common and not fatal to the culture. Scrape affected area away and reseal. If mould is extensive start a fresh culture from the healthy portion.
Culture Crashed
If no worm activity is visible and the substrate has dried or gone liquid the culture has crashed. This is why multiple cultures are essential — always have a backup at a different stage.
Worms Not Active
Cold temperatures slow microworm activity significantly. Move the culture to a warmer location — near a fish room heater or on top of a filter is often ideal.
Fish Not Eating Them
Some fish need time to recognise microworms as food. Deliver directly in front of the fish using a pipette rather than adding to the water column. Try fasting for 12 hours before introducing.
Why Buy From Jack's Aquatics?
Not all microworm cultures are equal. The density, health and activity level of a starter culture determines how quickly it establishes and how productively it performs in your setup.
Jack's Aquatics cultures are maintained in our UK mineral-supported systems — the same controlled environment we apply to all of our livestock. Our cultures are never imported and never wild sourced. Every pot is harvested from active, established cultures and dispatched on the same day they are packed.
- UK bred and maintained — no imports
- Active and productive from day one
- Consistent culture density across every order
- Dispatched Mon–Thu via Royal Mail Tracked 24
- Same welfare and quality standards applied to all our livestock
Ready to get started? Jack's Aquatics Microworm cultures are supplied in an active 2oz pot — productive from the day they arrive.
Shop Microworm CulturesQuick Reference
- Microworms are nematodes — not true worms, not animals under UK law
- Ideal size for fish fry and nano species — 1–2mm
- Survive 8–12 hours in freshwater — feed little and often
- Best substrate: instant mashed potato with a pinch of baker's yeast
- Ideal temperature: 20–25°C, dark and stable
- Culture lifespan: 3–4 weeks — always run multiple cultures
- Harvest using the wall scrape method — never add substrate directly to tank
- Always rinse in aquarium water before feeding
Important Context & Expectations
Culture performance varies depending on temperature, substrate preparation and ambient conditions. The guidance above represents best practice — results in individual setups may differ. Introduce microworms gradually and observe your fish's response before committing to a feeding programme.
All livestock supplied by Jack's Aquatics is dispatched in good health. Post-delivery outcomes depend on keeper conditions and management. For full delivery and claims terms refer to our Terms & Conditions.