A transparent flatfish larva swimming upright, before one eye migrates across its head.
A tall, thin, almost entirely clear fish with a silvery gut, swimming upright like an ordinary fish rather than lying flat. In many bothid larvae the first few dorsal fin rays are drawn out into long filaments that trail above the head, sometimes with small flags of tissue on them. The species is not determinable from a photograph and the family is usually as far as it goes; other flatfish families produce similar larvae, so even the family should be logged with some care.
The interest is what happens next. The larva starts life bilaterally symmetrical, with one eye on each side, and at settlement one eye migrates across the top of the skull to join the other. The skull bones remodel, the body pigments on one side and stays pale on the other, the fish tips over and takes up life lying on the sand. On a blackwater dive it is caught mid-way through that sequence, and a photograph taken from directly in front sometimes shows one eye already partly round.
Bothids are the lefteye flounders, and the adults are the flatfish a muck diver meets on the black sand. The larva looks so unlike the adult that the two are not obviously the same animal, which is much of the reason blackwater diving is worth doing at all.
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.
