Zebrafish Breeding Challenges: Seeking Advice

I'm experiencing significant issues with zebrafish breeding and would greatly appreciate any insights or advice from fellow researchers.

Here's a summary of my breeding attempts and the challenges I've encountered:

I've conducted five breeding attempts over the last three months, using parent fish approximately 1.5 to 1.8 years old. The break between breeding attempts was 10 days.

(See the table attached)

Total: Approximately 14,300 eggs and 11,000 larvae, resulting in around 2,000 surviving fish.

Observations:

1. Consistently high mortality rates between 8-19 dpf, varying slightly between attempts.

2. The water quality was initially identified as a major issue, particularly in the first attempt.

4. The larvae were started with one finger of water and gradually increasing water levels in the tanks

5. The flow-through system was generally opened at around 13 dpf, with one attempt at 10 dpf.

Questions and Concerns

1. Is an overall efficiency of about 15% (2,000 survivors from 14,300 eggs) normal for zebrafish breeding?

2. Could the age of the parent fish (1.5 – 1.8 years) contribute to the low survival rates?

3. Are there optimal practices for managing water quality and feeding during the critical 8-19 dpf period?

4. How can I improve survival rates, particularly during the identified critical period?

5. Are there any recommended adjustments to tank conditions, water management, or feeding protocols that could enhance survival?

I talked with a colleague who suggested that some larval mortality is normal, but my rates seem exceptionally high. I've attempted to address the issue by improving water quality and introducing live feed, but mortality rates remain concerning.

Any advice, insights, or suggestions would be appreciated. Thank you in advance for your help!