Brainless jellyfish actively fish: study

The virtually brainless irukandji jellyfish is actually clever enough to deliberately fish using a complex and effective technique, researchers have found.

Fishing can be a virtually brainless exercise, new research has revealed.

Irukandji jellyfish don't have a defined brain but are capable of casting a line, according to the first feeding study of the species.

Researchers discovered the deadly tiny species of jellyfish actively go fishing by stretching out their tentacles to form an invisible thread like a fishing line.

Evenly spaced along the tentacles are nematocyst clusters, which look like a series of fishing lures and are used to attract the attention of prey.

Researchers in the James Cook University study were surprised to find the deadly irukandji used such a highly successful fishing strategy given the species virtually has no brain.

"This species is small ... they're 96 per cent water, they lack a defined brain or central nervous system, and yet they're using their tentacles and nematocyst clusters like experienced fishers use their lines and lures," lead author Robert Courtney said.

Fish are quickly paralysed by the irukandji's powerful venom upon making contact with the nematocyst clusters.

In the laboratory-based study, researchers filmed Carukia barnesi, one of the five known species of irukandji, day and night using infra-red sensitive equipment to record their behaviour during complete darkness.

They found the irukandji conserved their energy at night and fished during the day.