According to this Islamic ruling and fatwa, all dead sea animals are halal. It does not matter if the fish dies naturally or due to some cause.

So, if chemicals are put into the water and the fish die because of it, they are still halal to eat. Islamic scholars have explained that fish remains permissible regardless of how it dies.

However, there is one condition. If eating such fish may cause harm, illness, or health problems, then it becomes haram بسبب the danger.

This fatwa clearly shows that permissibility depends on safety. If there is no harm, the fish is halal. If there is risk to health, it should not be eaten.