Hitchhiker ID

On recent trips to San Andres, Columbia, and to the Dominican Republic, I’ve been able to photograph these little hitchhikers on the fish in the photos below.

I know I’ve read about these organisms here on Wetpixel and elsewhere, but can’t seem to locate the information for identification of the critters. Is colouring an important factor in the identification of these critters or do they assume different colour phases while progressing through their life cycles?

If I remember correctly, there is also some discussion as to whether this organism is just a benign hitchhiker or parasite.

Any information with respect to these critters and their behaviors would be gratefully appreciated.

Thanks

San Andres, Columbia

Puerto Plata, Dominican Republic

They are parasitic Isopods.

They are parasitic Isopods.

Thanks for the quick reply.

I had an inkling that the word "Isopod" figured prominently in the identification, but for some reason, I just could get it nailed down.

If I remember correctly, there is also some discussion as to whether this organism is just a benign hitchhiker or parasite.

I just had a quick read up on these things. I didn't know they were such nasty little buggers.

My sympathies go out to the fish in these photos.