Xbox bedrock 1.16 Realms. Usually only 2 players but no more than 3. Place tropical fish from from buckets into constructed aquarium 8 deep with varying width from 1 to 8 blocks. Solid columns of water source blocks built with kelp. Fish stay for a few days of game play with logins/offs but eventually disappear. Not sure how long the intake time is. Had this happen two times so should be easily reproducible. Did not use name tags.
Related issues
Comments

Thank you for your report!
We're tracking this issue in MCPE-21416, so this ticket is being resolved and linked as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki – 📖 FAQs
-- I am a bot. This action was performed automatically! Please report any issues on Discord or Reddit