Why Some Fish Eggs Don't Hatch: Common Causes

A breeder asks why eggs from the same parents sometimes all hatch, sometimes none, and sometimes only a few—with occasional die-offs after hatching.

Top Factors Affecting Hatch Rates

1. Water temperature: Each species has a narrow optimal range. Too cold = slow development, fungus. Too fast = deformities, premature hatch.
2. Water quality: Ammonia >0, nitrite >0, pH swings, low oxygen = embryo death.
3. Fertility: Not all eggs are fertilized. Unfertilized eggs turn white/opaque and fungus.
4. Genetics: Inbreeding depression reduces viability. Rotate breeders.
5. Parental health: Malnourished or stressed parents produce poor-quality gametes.
6. Fungus/bacteria: Saprolegnia spreads from dead to live eggs. Methylene blue or Indian almond leaves help.
7. Predation: Parents or other tankmates eat eggs/fry.
8. Light: Some species need darkness; others indifferent.

What I Need to Diagnose Your Case

Please provide:
• Species
• Pond/tank size & setup
• Filtration & aeration
• Water parameters (temp, pH, ammonia, nitrite, nitrate, GH/KH)
• Spawning substrate
• Whether parents are separated post-spawn

General Best Practices

• Remove parents after spawning (most eat eggs).
• Use a dedicated hatching tank with gentle sponge filter.
• Add methylene blue (1 drop/gal) to prevent fungus.
• Maintain stable, species-appropriate temperature.
• Cull unfertilized (white) eggs daily with a turkey baster.

Without specifics, I can only list possibilities. Share your setup details for targeted advice.