Trouble shooting for ovulation fertilization and development


Female medusae don't spawn eggs

  • Medusae too young
    • Check gonads and confirm that they have oocytes
  • Light/Dark cycle is not controlled properly
    • Minimum 3 hours of dark environment for 24 hours/cycle
    • Short illumination (< 1 min.) doesn't induce ovulation
    • Oocytes may not be mature if you change the timer setting earlier. (jet lag)
      • Jellyfish will adapt to the new cycle in one day.
  • Not enough food

Female medusae spawns. But the ovulation takes too long (more than 30 min.)

Normally ovulation takes 10~15 min.
  • Salinity is low. Check it in the right range.

Egg size is small

  • Not enough food. Amount of feeding may have dropped in the last 1~2 days.
  • Medusae are too young.

Too few eggs

Normally one medusa spawns at least several eggs (100~200 from 30 medusae). You can expect 10~20 eggs/medusa.
  • Medusae are too young
  • Medusae are too old. Medusae that have spawned for more than 2 month might be replaced by younger medusae.
  • Not enough food. Amount of feeding may have dropped in the last several days.

Eggs don't get fertilized (no or few eggs start cleavage)


In any case, check the amount of sperm under binocular with dark-field illumination. See below depending on the results.
  • In the dish of male jellyfish before mixing with eggs. (BI)
  • After eggs are placed in the male sea water / sea water from male jellyfish dish is poured over eggs. (AI)

Q.S1 There is no spermatozoid (AI)

  • Male medusae are too young or too old.
    • Check male gonad under microscope. They usually have two layers: inner transparent layer and outer opaque layer. The outer layer will be disappeared or diminished when they get too old. The outer layer is a sign that males are actively producing spermatozoids.

Q.S2 There are a bit of sparmatozoids (AI, BI) or little spermatozoid (BI)

  • The cause of this problem is the same as for Q.S1
  • Increasing number of male medusae may simiply resolve this problems.
    • If you are adding sea water from male dish to a dish with eggs. (Sperm-to-Egg method)
      • Do the other way around: transfer eggs into a dish with male medusae. (Egg-to-Sperm method)
    • If you don't need to control the timing of fertilization
      • Put both male and female in a dish from the beginning.
  • See also Q.S3

Q.S3 There are plenty of spermatozoid but egg don't get fertilized.

  • The quality of eggs is bad
    • Confirm the salinity is in the right range. (This may affect to the quality of eggs.)
    • Change sea water.
    • If the treatment above don't help
      • Change to new female if they are old.
  • Male jellyfish are old (The quality of the spermatozoid may not be good.)
    • Change to new males