Why do fish sleep in nets?

Lexa Grutter/researcher

Some fish like the roundhead parrotfish – which makes its home in the barrier reef – spend up to one hour each evening making a “net” composed of mucus and wrap themselves in it. Thanks to some new Australian research, scientists believe they may have an answer for this rather strange behavior. The research comes from the University of Queensland, and was published in the journal Biology Letters, and dictates that these amazing fish make these “nets” to help protect them from attacks from parasites.

Earlier on, scientists thought that this mucus “net”, which resembles something like a balloon filled with JELLO, helped to protect the fish from predators. It was originally believed that the mucus covered up the fish’s smell, and helped it remained hidden from things looking to eat it.

However Dr Lexa Grutter and a team of colleagues, always pondered just how the transparent, fragile, and easily removed mucus “net” could possibly protect the fish from any hungry predator such as eels or sharks.

Well, they seemed to have stumbled upon the answer. Parrotfish are constantly under attack from gnathiids – a really tiny long thin isopod which is a distant relative of the slaters and pill bugs we can find in most gardens.

These gnathiids are much like underwater mosquitoes, and can suck the blood of a poor parrotfish for up to an hour, and in some cases give them a disease strikingly similar to malaria.

Grutter and her crew discovered that these mucus “nets” act much the same as our mosquito nets we throw over our beds during the summer, to keep the pesky bugs away.