Fish get sick quietly — by the time you see deaths, the problem has usually been building for days. The key is spotting trouble early and, better still, preventing it with clean water and good care.

1. Common diseases

  • Bacterial infections (germs) — fin rot, open sores and dropsy (a swollen, bloated body), usually linked to poor water quality or injury.
  • Fungus (mould) — shows as white cotton-like growths on skin or eggs.
  • Parasites (small pests that live on the fish) — cause scratching, fins held close to the body and sluggish, lifeless fish.

2. Early warning signs

  • Fish gasping at the surface or swimming strangely
  • Loss of appetite
  • Sores, spots or white growths
  • Sudden deaths, especially after rain or heat

3. Pests and predators

Birds, snakes and monitor lizards eat fish, while weeds and snails can carry disease. Netting over the pond, fencing and regular clearing all help.

4. Prevention beats cure

  • Water quality — change the water or keep it well-aired regularly; avoid feeding too much, which pollutes it.
  • How many fish you keep — overcrowding stresses fish and spreads disease.
  • Quarantine — keep new fish separate for a while before adding them.
  • Clean gear — nets and buckets carry disease between ponds.

If disease strikes, ask a vet who specialises in fish or an experienced hatchery for the right treatment — don't guess with chemicals. For the full cycle, see our catfish farming guide and fish pond construction.

Key takeaways

  • Disease is usually a water-quality problem first.
  • Watch for gasping, appetite loss and sores.
  • Prevent with clean water, the right number of fish and keeping new fish separate.
  • Net and fence the pond against predators.