When fish die why do they get covered in fuzzy white things around their body?

The fuzzy white things you see on dead fish are a type of fungus called Saprolegnia. It's a common water mold that thrives in moist environments and feeds on decaying organic matter, like dead fish.

Here's why it happens:

* Dead fish are vulnerable: When a fish dies, its immune system shuts down, making it susceptible to infections.

* Saprolegnia takes advantage: Saprolegnia spores are present in most aquatic environments. When they encounter a dead fish, they quickly colonize its body.

* Fuzzy growth: As the fungus grows, it forms a white, cottony layer over the fish's skin and gills.

It's important to note that:

* Saprolegnia doesn't kill the fish: It's a secondary infection that occurs after death.

* It's not contagious to live fish: Saprolegnia is a saprophyte, meaning it only grows on dead or decaying matter.

While the fuzzy white growth is an indicator of a dead fish, it's not harmful to other living organisms.