Man-of-war Fish

• It tolerates doses of Portuguese man o' war venom that would be lethal to other fish of its size, though it is not immune: it moves carefully among the tentacles and can die if it becomes entangled.
• It devours its host's tentacles, so the relationship is more parasitic than symbiotic.
• The juveniles shelter among the shorter and more dangerous tentacles, and the adults stay beneath the float.
• It lives among the tentacles of the Portuguese man o' war, and it does not merely shelter there: it eats its tentacles and its gonads.
• Its resistance to the venom is around ten times greater than that of other fish, and it has at least one antigen against the toxin, but it is not immune: it actively avoids the large tentacles, the dactylozooids.
• And it does not manage this with mucus, as the clownfish does with its anemone, but by dodging them. It has 41 vertebrae, an extremely high count that gives it extraordinary flexibility, and it swims mostly with its pectoral fins, something typical of fish specialised in manoeuvring in tight spaces.
• Each man o' war can carry five to ten adults, with numerous juveniles around it.
• It changes its way of life completely as it grows: the juvenile is pelagic, showy and lives at the surface, while the adult moves to live near the bottom, at great depth, with a far more subdued greyish appearance.

Skeleton type

Vertebrate - internal bony skeleton (fish)

Habitat and environment

Surface waters of the open sea, associated with floating siphonophores

Sources consulted: Wikipedia (es): Nomeus gronovii