How to Hatch & Store Semi-Annual Killifish Mop Spawning Eggs

This guide is based on the transcript from the YouTube video:
“How to Hatch Killifish Eggs / Collect and Store Semi-Annual Killifish Mop Spawning Eggs”

It focuses specifically on semi-annual mop-spawning species (also called “switch spawners”).

🐟 Understanding Semi-Annual / Switch Spawners

Semi-annual killifish:

• Are often peaceful outside breeding
• Can hold their own in community tanks
• Become very aggressive during breeding
• Are known as “switch spawners”

“Switch spawning” means they may:

• Lay eggs in mops (plants in nature)
• Or lay eggs in peat / muddy substrate

For this guide, we focus on mop spawning.

⚠️ Breeding Behaviour Warning

During breeding:

• Males become extremely aggressive
• They will attack other males
• They may harass females to death

Best practice:

• 1 male to 2–3 females
• Species-only breeding tank

🧶 Collecting Eggs from the Mop (Preferred Method)

This is the breeder’s recommended method.

Step 1 – Remove and Dry Mop

1. Remove mop from tank.
2. Gently squeeze out excess water.
3. Let it sit for a couple of minutes.

Eggs are very hard to see when wet.

Tip:

• Use 3× magnification glasses if needed.
• Wash hands thoroughly before handling.

Step 2 – Remove Eggs

• Gently pick eggs from mop with fingers.
• Place into small shallow container.
• Use tank water.

⚠️ Important:
If breeding multiple species, eggs can stick to fingers and contaminate batches.

Always:

• Work carefully.
• Label containers immediately.

💧 Water Incubation Method (2 Weeks)

This is the breeder’s preferred method.

Setup:

• Shallow container
• Room temperature
• Away from direct light

Daily Maintenance:

• Check eggs daily.
• Remove white/dead eggs immediately.
• Perform water change after removing initial dead eggs.

Why Eggs Fungus:

• Unfertilised eggs rot first.
• Bacteria spreads quickly in stagnant water.

Optional Treatments:

• Methylene blue (preferred)
• Acriflavine
• Malachite green

Good oxygenation + removing dead eggs = best defence.

Hatching Timeline

• About 2 weeks (temperature dependent)
• If eggs collected over time → fry hatch at different times

⚠️ After 3–4 days:
Larger fry may eat smaller ones.

🌱 Peat / Coco Fiber Incubation (3–4 Weeks)

Alternative method.

Why Some Breeders Prefer It:

• Less fungal spread
• Eggs separated in substrate
• Fry hatch more evenly in size

Using Coco Fiber (Preferred Over Peat)

The breeder prefers coco fiber over peat because:

• Less acidic
• More neutral
• Encourages infusoria when wetted

Preparation:

1. Soak coco brick overnight.
2. Squeeze until damp (like pipe tobacco).
3. Must not be wet.

Too wet = fungus.

Incubation Process

1. Collect eggs.
2. Treat briefly in shallow water with antibiotic.
3. Transfer eggs onto damp coco fiber.
4. Store in sealed, dark container.
5. Check weekly.
6. Incubate 3–4 weeks.

When eggs “eye up”:

• Add water (2–3 inches deep)
• Eggs hatch.

Important Warning

Do NOT try to re-dry eggs.

These are semi-annual species — not true annual killifish.

You usually only get one hatch opportunity.

Re-drying = dead eggs.

🪴 Peat Spawning Method

If fish laid eggs directly in peat:

1. Remove peat from tank.
2. Place into fine mesh net.
3. Squeeze until damp (not wet).
4. Store in sealed container.
5. Incubate ~4 weeks.

When eggs eye up:

• Add shallow water to hatch.

Acidity Concern

Some breeders remove fry immediately because peat water may be too acidic.

Coco fiber is safer and more neutral.

🧵 Whole Mop in Plastic Bag Method

Another method:

1. Squeeze mop.
2. Place entire mop in sealed plastic bag.
3. Store 3–4 weeks in dark.
4. Check for eyed eggs.
5. Submerge to hatch.

Breeder does NOT recommend this method because:

• Food trapped in mop rots.
• Bacteria levels rise.
• Fungus spreads easily.
• Hard to identify fertilised eggs.

Very few species require this method.

🪴 Leave Eggs in Planted Tank Method

Some breeders:

• Set up heavily planted tank.
• Allow fish to breed naturally.
• Remove adults after 2–3 weeks.

Problems:

• Many species eat fry.
• Hard to feed microfoods in planted tank.
• High fry mortality.

🏆 Preferred Method Summary

The breeder’s choice:

✔ Collect eggs from mop
✔ Incubate in shallow water
✔ Remove dead eggs daily
✔ Use methylene blue if needed
✔ Hatch in 2 weeks

Why?

• Easier to monitor
• Faster hatch
• More control

❗ Important Final Advice

If eggs keep fungusing:

It may not be your fault.

Young pairs often:

• Produce poorly fertilised eggs.

After a few spawning cycles:

• Fertility improves
• Egg batches increase
• Success rate rises

Do not give up.

📊 Quick Comparison

Method	Time	Risk	Control	Recommended?
Water incubation	~2 weeks	Fungus risk	High	⭐ Best
Coco fiber	3–4 weeks	Timing critical	Moderate	Good
Whole mop bag	3–4 weeks	High fungus risk	Low	Not ideal
Natural tank hatch	Variable	Fry eaten	Low	Risky