A deep-sea fish whose larva swims in the top of the water column trailing fin rays four times its own length.
Adult ribbonfish are long, thin, silver, deep-living and almost never seen alive. The larvae are one of the great blackwater subjects, and look nothing like the adult: a small transparent body with the first few dorsal rays and both pelvic fins drawn out into streamers several times the length of the fish, each streamer carrying a row of swollen, pigmented blobs along its length.
Nobody is certain what the streamers are for. The two standing explanations are that the blobs mimic a chain of small gelatinous animals and so distract a predator away from the body, or that they simply increase the larva’s apparent size. Neither has been tested properly, which is a fair summary of most of what is known about larval fish behaviour in open water.
The larvae in this region are usually Desmodema polystictum or a Trachipterus species. They are not separable in a photograph, so the family is what this entry claims. As the fish grows the streamers are absorbed and the animal drops into deep water, which is why the adult is a stranding record and the larva is a dive.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
