> Does anyone know offhand the number of pin bones in each of the common
> salmonids -- Atlantic, chinook, coho, chum, pink, rainbow
trout/steelhead? Is
> it a fixed number per species/genus? How is the number related to the
number
> of ribs? I am also assuming that the number of pin bones is fixed by the
time
> the fish reach adult shape, and that they grow in size but not in number
as
> the fish grows. If anyone has this information at their fingertips, or
can
> refer me to where to look it up, I'd appreciate the help.
I can give you a somewhat incomplete answer. Pin bones, referred to as
'inter-muscular bones' in zoology textbooks, are usually associated with
the pleural ribs, those that enclose the belly cavity, of a fish, though in
some species they are associated with the vertebrae to which the pleural
ribs are attached. I write 'associated' because they do not appear to be
fused with the ribs or vertebrae, but connected by fibrous tissue. They are
connected to about the first half, by number, of the ribs. The general
textbooks of zoology I have do not go into detail so I looked in on a
natural history museum to see what it had. There were mounted skeletons of
a few species of fish. Because pin bones are not fused to the skeleton you
cannot be certain that the taxidermist has recovered all of them. The most
convincing was that of a perch with 9 pin bones, on each side, attached to
the pleural ribs. The skeletons of cod and haddock had the pin bones
attached to the pleural ribs by wire and I can't be sure that all the pin
bones were present, but there were 9 and 11 bones in the haddock and cod
respectively. There was a skeleton of the Atlantic salmon, Salmo salar, and
in that species the pin bones are attached to the vertebrae. There were 12
on each side, and 26 pairs of pleural ribs.
If you need exact numbers I think you will have to determine them yourself.
I suggest 3 possible methods. You won't need adult specimens; juveniles
will do unless you want to confirm that pin bones in an adult are
sufficiently large to be a nuisance. (1) Get a friendly vet to x-ray some
fish. This is a very good method to show the orientation as well as the
number. (2) Cut off fillets and digest the flesh with papain or pepsin.
Recover and count the bones. (3) Soak a fillet in dilute alkali and the dye
alizarin. The alkali clears the flesh and makes it translucent, and the
alizarin stains the bones red. This is a rather messy method as the excess
dye has to be washed out by leaching the fillet in dilute alkali. The first
is the most convenient and satisfactory. The second works quite well and
can be done in the kitchen - some casserole dishes, a supply of meat
tenderiser papain, and a hot plate to warm the mixture up to about 50C. It
is no good feeling for the bones in a fillet; you will miss the smaller
ones towards the posterior.
Peter Howgate