Fish parasite? Gymnodoris nigricolor

March 21, 2000
From: Atsushi Ono

Dear Bill
This dorid is a parasite on some species of gobies. I am pretty sure this is Gymnodoris nigricolor Baba,1960. This goby is Amblyeleotris steinitzi (Klausewitz).
I have never seen G. nigricolor crawling, it is always parasitic on gobies.
They are about 6 to 8mm long, found 22m depth.

Atsushi Ono

Ono, A., 2000 (Mar 21) Fish parasite? Gymnodoris nigricolor. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Atsushi,
Thanks for the wonderful photos. Bob Bolland has a series of photos of this remarkable association between a nudibranch (Gymnodoris nigricolor) and fish (gobies).

I remember when I first saw an article on this association, I thought perhaps the Gymnodoris had got 'spiked' on the fish after collection. It is a remarkable relationship which is now considered to be a parasitic rather than symbiotic relationship.
Best wishes,
Bill Rudman.

Rudman, W.B., 2000 (Mar 21). Comment on Fish parasite? Gymnodoris nigricolor by Atsushi Ono. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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