What is going on? Why are my fish dying?
Springtime diseases and oxygen losses in fish ponds are common throughout the Southeast. During winter, fish eat very little, and their immune system is suppressed. When temperatures increase, bacteria present in the pond attack fish that are weak. Abrupt temperature fluctuations also suppress fishes' immune systems.
Many ponds have partial die-offs during the spring due to low oxygen. Algae produce oxygen in sunlight; under cloudy conditions, oxygen production decreases. When pond water warms too quickly, cold-water algae can die off abruptly, causing low oxygen levels for several days.
What to look for:
If big fish are dying and small fish are not, the most likely cause is low oxygen.
If all sizes of fish are dying, the most likely cause is a disease.
If fish have discoloration or sores, the most likely cause is a bacterial disease.
If small fish die before larger fish of the same species, a toxic substance may be involved.
What can I do?
Some feed stores can supply medicated feed to treat bacterial disease problems.
For low-oxygen problems, pumps can re-aerate water from shallow depths by spraying it back into the pond. Aerated well water (splashed or sprayed) can be used to flush small ponds.
The LSU AgCenter and the LSU College of Agriculture