After retiring from the Navy I started a new career as a fishmonger in
the retail fishing industry. I have worked in this new field for two
years now. While researching information on Escolar (fish from Gulf of
Mexico, South America, Australia...) for a sale my store is having I
became interested in the high oil content that this fish holds. The
articles on different websites mentioned that some people have a
digestion problem with this fish especially if eaten too much during
one sitting. Problems are usually indentified within 1-90 hrs after
consumtion of the fish. Problem signs most often associated with
eating to much of this fish are stomach unsettleness, to diaheria. The
diaheria will usually have a waxy orangeness to the oily liquid. This
waxy oily liquid was mentioned to be undigestable wax esther found
within the fish.
 Although black cod and mackarel are high oil fishes patrons do not
usually have the same difficulty with the digestion of these fishes.
 I would like to brief my co-workers, manager, and Store director as
soon as possible with a full understanding of what is wax esther.

An esther is made by dehydration of an acid and an alcohol. Regular
fat (like in mackarel) is a mixture of triglycerides. A triglyceride
is a glycerol-esther with three fatty acids attached. In escolar the
glycerol (3 carbon atoms) is replaced by long-chained fatty alcohols
(14-22 carbon atoms); thus making them indigestible. This indigestible
wax causes diarrhea much like over-consumption of food with Olestra.
(Olestra is also an indigestible "wax", an esther between sugar and
oleic acid.)

http://www.bgvv.de/cm/208/gesundheitsbeeintraechtigungen_durch_buttermakrelen.pdf

:-) As2O3

A wax is an esther. An ester is an alcohol and a carboxylic acid
combined. An alcohol is any carbon chain with an -OH attached, and a
carboxylic acid is a carbon chain with a carbon bound to -OH and also
double bonded to oxygen. Look at the larger image on this site:
http://www.elmhurst.edu/~chm/vchembook/554wax.html
The difference in waxes basically depends on the number of carbons in the chains.

Waxes are usually used by sea creatures because it solidifies in cold
water, thus adjusting the balast for flotation and changing the
density of the fish (or whale, or whatever) to stay at the appropriate
level in the water. It easily softens in warmer water, allowing the
fish to adjust its balast for the water it is floating in.

It causes diarrhea because longer fatty acid chains can be difficult
to absorb, and thus they remain in the intestine. This creates an
osmotic pressure that pulls water out of your blood and into the
intestine, causing diarrhea.

Hope that helps!