Image Credit: Dominique Roche

Attack of the parasitic face-huggers

  • BY Becky Crew |
  • July 17, 2014

There's a little something eating your face: scientists would love to warn fish shackled with 'face-huggers'.

Contributor
Bec Crew

Becky Crew is a Sydney-based science communicator with a love for weird and wonderful animals. From strange behaviours and special adaptations to newly discovered species and the researchers who find them, her topics celebrate how alien yet relatable so many of the creatures that live amongst us can be.

THE BRIDLED MONOCLE BREAM is a little reef fish found off the coast of Western Australia and in the northern Great Barrier Reef. Named for the beautiful bright yellow stripes that run along its dark grey back, this fish has found itself in the rather uncomfortable position of being the preferred host of a parasite called Anilocra nemipteri.

These crustaceans hook onto the scales of their hosts just above their eyes and feed off the nutrients they chew out of their faces. Relatives of the infamous 'tongue biting' isopod, they've been given a pretty apt nickname by blogger Tommy Leung over at Parasite of the Day: 'face-huggers'.

And these sizeable horrors – they can grow up to 23mm long – are by no means rare. In some parts of the Great Barrier Reef, up to 30 per cent of bridled monocle breams are afflicted.

The Anilocra nemipteri parasite will often remain attached to its host's face for several years, so a couple of years ago PhD candidates Sandra Binning and Dominique Roche from the Australian National University set out to determine exactly what damage they were doing during this time.

Testing the effects of living with a face-hugger 

They attached plastic parasites to bream in their lab and set them up in little 'fish treadmills' to see how they moved. Devices were attached to determine how much oxygen was being consumed by their artificially parasitised subjects.

"Oxygen consumption is a proxy for energy consumption: if a fish consumes more oxygen, it is burning more fuel and will need to eat more," Binning says. "For fish, eating more means you may be more exposed to predation and have less time for other important activities, such as attracting mates."

The pair reported that not only did the parasites create drag for the fish when it swam on the treadmills, causing it to consume more oxygen and therefore energy, but if a host was lucky enough to finally escape its clutches, it would be left with a gaping, deep wound in its face. They also found that in the wild these parasites severely stunted the growth of their hosts, foiled their reproductive efforts and would often kill their hosts if they remained attached for too long.

All of which sounds pretty rough, but it's still preferable to being the victim of a tongue biter. At least the face-hugger doesn't, you know, chow down on the bream's tongue, eat the whole thing and then attach itself to the tongue-stump so it can feed off the morsels of food the fish puts into its mouth. At least the face-hugger doesn't do that.