First check
Water quality and oxygen
Next check
Whether every fry can physically reach suitable food
Hidden pressure
Size differences and overcrowding
Best tool
Daily observation with honest loss records

Find when losses occur

“The fry keep dying” is too vague to solve. Record whether losses occur in the first day, after the yolk is used, after a food change, during a growth spurt, after grading or following maintenance. Timing narrows the likely failure.

Use mature, gentle filtration

Prepare the fry system before spawning or birth. A mature sponge filter provides biological filtration with low intake risk. Keep flow strong enough for gas exchange but not so forceful that small fry spend all day fighting the current.

Match food to mouth size and behaviour

Food must be small enough, available where the fry feed and offered before weakness begins. Tiny portions several times a day can improve access, but uneaten food can destroy water quality. Observe bellies and feeding response instead of assuming food added equals food eaten.

Clean without destabilising

Remove dead fry and accumulated food promptly. Use careful small water changes matched for temperature and treated appropriately. Aggressive cleaning can strip a young system or shock fry; no cleaning allows waste to build. The correct routine is frequent, controlled and recorded.

Control density and size differences

As fry grow, larger individuals dominate food and space. Grade by size when the difference becomes meaningful. Increase volume, filtration and maintenance before the tank is visibly crowded. Do not use high survival as an excuse to postpone housing plans.

Daily fry check

  • Count visible losses and remove them.
  • Observe swimming, breathing and group distribution.
  • Confirm every area receives food.
  • Check temperature and equipment operation.
  • Inspect bottoms and corners for waste.
  • Record unusual colour, shape, appetite or growth.

Compare batches honestly

Track parent pairing, birth or hatch date, initial count, first foods, tank, water changes, growth milestones and losses. A “good batch” should be repeatable. If success cannot be linked to a recorded routine, it is still mostly luck.

Research and review

This guide is original AquaNexus writing. The care framework was checked against the following reference types and then rewritten for practical aquarium use.

See the full research register and source-use policy →

Care note

Aquariums vary. Use this guide as a practical starting point, observe your livestock and plants, and make changes gradually. For serious illness or unexplained losses, seek advice from a qualified aquatic veterinarian or experienced local professional.