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Commensal fish and Mimic Octopus? Science in action!

By Richard Ross - Posted Jul 25, 2011 08:00 AM
After my investigation I think the fish is a jawfish, Family Opistognathidae, Stalix histrio - Black Marble Jawfish. But why is the fish was swimming together with the Mimic for about 15 minutes??
Commensal fish and Mimic Octopus? Science in action!

A commensal fish?

Last week Godehard Kopp posted the video above of a Mimic Octopus, Thaumoctopus mimicus, and an un identifiable fish swimming amongst its arms at the divesite Jahir in the famous muck diving area of Lembeh Strait, Sulawesi Indonesia (the video of the octopus and fish starts at about. :44). Kopp followed the one octopus and fish for 15 minutes filming what appeared to be a previously unknown fish/octopus comensal relationship – a relationship in which one organism derives a benefit while the other is unaffected. Flurries of emails lit up the interwebs as fish and cephalopod and fish enthusiasts tried to determine what was actually going on in the video. Is this a commensal relationship or is something else going on?

The colors of the fish were so matched to the arms of the octopus, that it could easily be thought that this fish must have a previously un-described commensal relationship with the octopus. On the other hand, there are small fishes that swim around foraging octopus arms in search of an easy meal, so it could be that this was simply taking advantage of a possible easy meal as the octopus made its way across the muck. On the third hand, these octopus have been photographed and filmed so much in this area of the world that it might be hard to believe that this behavior had never been seen before. Perhaps the fish happened to be in the wrong place and got scared as the Kopp moved to film in, and was trying to hide in the frist thing it found – the octopus.

Initially, the fish was thought to be some kind of Blenny, but quickly the tide turned and it was thought to be some kind of Jawfish. Soon a more positive ID was soon made: Black Marble Jawfish, Stalix histrio (or another fish in the Stalix genus) shown below from Indonesian Reef Fishes by Kuiter, R.H. & T. Tonozuka. (2001). Since both the fish and the octopus live in, and are trying to blend in with, the same muck background, it makes some kind of sense that the two should share the same kinds markings and color patterns. Of course, there could still be some relationship between the fish and the octopus, more study is needed, but even if this isn’t commensal, it seems to be a brand new behavior for the fish (and possibly a new fish species!)

It was great to watch science in action in regards to this video. Observation, hypothesis, evidence, discussion, new hypothesis changing minds – science rules!

Author: Richard Ross

Richard Ross, the 2014 MASNA Aquarist of the Year, is a Senior Biologist at the Steinhart Aquarium in the California Academy of Sciences where he cultures and cares for exotic cephalopods, fish & coral, participates in ongoing field work on coral spawning, animal collection & transport, and manages tropical saltwater displays including the 212,000 Philippine Coral Reef exhibit. He is a prolific writer and dynamic speaker, authoring academic papers and a catalogue of articles on aquarium and reef related educational topics including his Skeptical Reefkeeping series which focuses on critical thinking, responsibility and ethics of aquarium keeping. His work has been covered by mainstream media outlets including Scientific American, National Geographic, Penn’s Sunday School and Fox News.

Website: www.packedhead.net.

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