Yes to the first question. Shark meat is palatable and
nutritious if properly prepared. In some countries shark meat is
marketed under its common name, in others it is marketed under various
names. The fish in England's "fish and chips" is sometimes dogfish
or school shark (although this would be considered low quality "fish & chips". True "fish and chips" consists of cod, haddock (the 2 most popular) and also plaice). The prejudice against shark meat arises from
a distaste for the scavenging habits people attribute to sharks, and to
the fact that the meat spoils quickly. The meat of certain species is
apt to be strongly flavored, a characteristic that may be reduced by
icing for 24 hours, then soaking for two hours in brine Dry salted
shark has become a staple food in some countries where salt cod was
formerly popular. But shark liver should never be eaten - its high
concentrations of vitamins can cause illness in humans. It is only a
rumor that the hammerhead is poisonous.
Commercially, the name has come to signify any small
herring-like ocean fish. In the United States, it is mandatory that
when the name "sardine" is used on a can, the country or state of
origin be listed, and a statement must appear that identifies
preserving and flavor supplements.
There are seven commercial and sport-caught tunas, as well as
several related species, all of which are members of what is called the
scombrid family. Commercially caught tunas consist of albacore, bigeye,
blackfin, bluefin, bonito, skipjack, and yellowfin. Yellowfin, taken in
the eastern Pacific and tropical Atlantic, makes up the biggest U.S.
commercial catch. Albacore, caught in the eastern Pacific, is the true
"white-meat" tuna; skipjack, caught throughout the world in tropical
and subtropical waters, makes up the second largest U.S. commercial
catch; bigeye is caught mostly in tropical waters; blackfin is caught
commercially only in the Caribbean and off South America; the very
large bluefin (rod-and-reel record, 1,040 pounds) is a highly prized
sport catch in the Atlantic and Pacific; and the widely distributed
bonito is used largely as pet food.
Yes, all species do, but scales are so small over most of the
body as to be nearly invisible. Prominent scaling appears only around
the head, on the cheeks, and in a triangular area on each side of the
body near the head.
Tuna images courtesy of "Regulatory Fish Encyclopedia, Office of Seafood and
Office of Regulatory Affairs, Food and Drug