Why does this happen and how do I prevent it?
Test your water quality. Water quality issues are often invisible to the human eye and can have dramatic effects on the wellbeing and health of your aquarium without any obvious warning. Testing regularly can allow you to address water quality issues before it is too late.
Look for obvious physical symptoms on the dead fish which can suggest the cause if death. If there are physical symptoms on the fish, consider another diagnosis for the death and treat the remaining fish accordingly.
If only one fish in your tank has died consider the age/lifespan of the fish as, like all animals, fish will just die from old age.
Some other issues that could cause unexplained fish death are:
- De-oxygenation – in this case often only the larger fish will have died because they have a higher oxygen requirement.
- Acute systemic bacterial infection – fish die before exhibiting many physical symptoms.