For what it's worth, I've drawn a badly-portrayed piccy of the fish as I
roughly remember it, for those who was interested. I won't post it up
here for fear of upsetting those who are rightly anti-binary! If you
fancy helping just drop me a line and I'll email it.

I also found plenty of pictures that show the southern stingray I also had
in the same field of view. These things seem awfully big, and the fish
was bigger than the stingray. The mask I know foreshorterned my vision
(judging by looking at my own arm and the depth of the water) which
probably means that this thing might have been over 6ft long... The ray I
saw looked the same (maybe slightly smaller) as the one in:

http://www.cayman.org/divesite/stingray.htm But the only other thing in
frame for scale for me was this mofo fish.

It was in fairly shallow water (naybe twice the depth of the water in the
photo above), but I got the impression it was lost because it wandered out
to the deeper trench which was only a few yards away. The beach I was at
in Grand Cayman went from ankle-deep to waist-deep over about 100 yards,
then dropped suddenly down to 8-10 foot or so, and then dropped again to a
depth I couldn't accurately tell - 20ft or more probably.

Cheers

Bennett (not obsesseed yet, but getting there)