PLATE IV.[a]How to Cut Open and Mount a Fish.]
You will find that the ventral fins are joined together in the flesh by a strong bony arch, called the pubis, and this must be divided through the middle so as to entirely separate the fins. The anal fin-rays must now be cut loose from the interior rays (called interhæmal spines), which are really their bony foundation. The ventral fins must also be cut loose from the pubic bones at the point where they are articulated. Now take the cut edge of the fish skin between the left thumb and forefinger, and with the cartilage-knife carefully cut the skin free from the flesh. Be careful not to disturb the white layer of color pigment which is spread like a silver lining of feeble tin-foil over the inside of the skin. This is what gives the fish its silvery color, and if skinned off or scraped away the skin will look like colorless parchment. Whatever you do, do not disturb that color lining. Proceed with the skinning until the skin has been detached from the entire upper side of the fish. This brings you to where the dorsal and caudal fins are inserted.[6]
Now turn the fish over, and proceed as before, as far as you can go. You presently reach the caudal fin, which must be cut loose from the end of the vertebral column as far back in the skin as possible. When this has been done, the skin and the fleshy body still hang together by the attachment of the rays of the dorsal fin to the interhæmal spines. Cut these apart with the scissors, from back to front, close up to the skin, which brings you to where the vertebral column joins the skull. You will make very short work of that, which frees the fleshy body from the skull. Now scrape away the surplus flesh from the inside of the skin, wash it thoroughly, remove the gills (if they are not to be studied), and lay the skin flat upon its side in your tank of alcohol.
By thus preserving the skins of fishes, instead of whole specimens, a great number of really large specimens can be preserved in a small quantity of alcohol, for at the last they can be packed together, heads and tails, precisely like sardines.
Skinning Cartilaginous Fishes.—Sharks, Rays, etc.—The skinning of a shark or saw-fish calls for no special instructions in addition to the foregoing, except that the long, narrow, pointed tail requires to be slit open along the right side of its upper lobe for a considerable distance. Remember the principle that wherever there is flesh, a way must be made so that it can be removed, or at least reached from the inside by the preservative. Of the skull, nothing is to be left attached to the skin
except the jaws. The skeleton is wholly of cartilage instead of bone, and is easily cut through.
The extremely flat, circular-bodied ray, also with a cartilaginous skeleton, must be opened on the underside by two cross cuts at right angles to each other, one extending from mouth to tail, and the other from side to side. The fin rays are very long stems of cartilage, set so closely together as to form a solid sheet of cartilage extending from the thoracic skeleton out to the extremities of the fins, which taper out to nothing. The thoracic skeleton gives shape to the body of the ray, particularly the back, and it must be left in place, with the skin of the back attached to it. Cut through the fin rays where they join the body, and this will enable you to skin down each side of the fish until you get so near the outer edge there is no longer any flesh. Stop at that point, cut the flesh away from the fin rays, and cut away as much of the fin rays themselves as you please.