"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

October 15, 2010

October 15 - Nerocila acuminata

Nerocila acuminata is a parasitic isopod related to Cymothoa exigua, the infamous "tongue-replacer". While N. acuminata doesn't have the morbid habit of replacing the tongue of its host with itself, that certainly doesn't make it more endearing. This isopod clings onto the skin of its fish host, feeding on blood and tissue. When it detects a potential host, this parasites becomes a fish-seeking missile - it launches itself at the target fish like a guided torpedo, making precise directional and speed adjustments to ensure it lands on its target with claws outstretched . Upon contact, the isopod starts digging in, causing terrible, terrible damage to the skin of its fish. In addition to damaged tissue and blood loss, such aggravated injuries can often lead to secondary infection by bacterial infection. Compared with the "tongue-biter", this parasite is one nasty customer.

Contributed by Tommy Leung and photo by Peter Bryant.


  1. hello susan.
    how does this parasite swims in the water?

  2. Much like other non-parasitic isopods, by moving its abdominal limbs (called pleopods) in a wave-like, rowing motion.

  3. Hello from Reddit, we found your blog and we were hoping you knew if this http://www.reddit.com/r/Unexpected/comments/1itv7m/saw_this_in_rfunny_its_better_here/ brief glimpse was the same parasite?

  4. Hi, it looks superficially like a cymothoid isopod (the family which the above species belongs to), but I don't know if that gif (?) is real. I've seen that gif going around - it's where a guy was holding a fish's mouth and an isopod jump out and latch on to his hand?

    I don't think they are capable of doing that - they're not all that agile out of the water, and certainly not agile enough to jump so quickly from a fish's mouth on to a dude's hand.

  5. Is it safe to eat a fish with one of these things on it???

    1. Yes, it's just a small crustacean - like a shrimp or a small crab, so it's actually edible. You can treat it a side dish or a bit of garnish.