An introduction to the study of fishes

by Albert C. L. G. Günther

The spirits used during this all-important process of preservation loses, of course, gradually in strength. As long as it keeps 10° under proof it may still be used for the first stage of preservation, but weaker spirits should be re-distilled; or, if the collector cannot do this, it should be at least filtered through powdered charcoal before it is mixed with stronger spirits. Many collectors are satisfied with removing the thick sediment collected at the bottom of the vessel, and use their spirits over and over again without removing from it by filtration the decomposing matter with which it has been impregnated, and which entirely neutralises the preserving property of the spirits. The result is generally the loss of the collection on its journey home. The collector can easily detect the vitiated character of his spirits by its bad smell. He must frequently examine his specimens; and attention to the rules given, with a little practice and perseverance, after the possible failure of the first trial, will soon insure to him the safety of his collected treasures. The trouble of collecting specimens in spirits is infinitely less than that of preserving skins or dry specimens of any kind.

When a sufficient number of well-preserved examples have been brought together, they should be sent home by the earliest opportunity. Each specimen should be wrapped separately in a piece of linen, or at least soft paper; the specimens are then packed as close as herrings in the zinc case, so that no free space is left either at the top or on the sides. When the case is full, the lid is soldered on, with a round hole about half an inch in diameter near one of the corners. This hole is left in order to pour the spirit through it into the case. Care is taken to drive out the air which may remain between the specimens, and to surround them completely with spirits, until the case is quite full. Finally, the hole is closed by a small square lid of tin being soldered over it. In order to see whether the case keeps in the spirit perfectly, it is turned upside down and left over night. When all is found to be securely fastened, the zinc case is placed into the wooden box and ready for transport.

Now and then it happens in tropical climates that collectors are unable to keep fishes from decomposition even in the strongest spirits without being able to detect the cause. In such cases a remedy will be found in mixing a small quantity of arsenic or sublimate with the spirits; but the collector ought to inform his correspondent, or the recipient of the collection, of this admixture having been made.

In former times fishes of every kind, even those of small size, were preserved dry as flat skins or stuffed. Specimens thus prepared admit of a very superficial examination only, and therefore this method of conservation has been abandoned in all larger museums, and should be employed exceptionally only, for instance on long voyages overland, during which, owing to the difficulty of transport, neither spirits nor vessels can be carried. To make up as much as possible for the imperfection of such specimens, the collector ought to sketch the fish before it is skinned, and to colour the sketch if the species is ornamented with colours likely to disappear in the dry example. Collectors who have the requisite time and skill, ought to accompany their collections with drawings coloured from the living fishes; but at the same time it must be remembered that, valuable as such drawings are if accompanied by the originals from which they were made, they can never replace the latter, and possess a subordinate scientific value only.

Very large fishes can be preserved as skins only; and collectors are strongly recommended to prepare in this manner the largest examples obtainable, although it will entail some trouble and expense. So very few large examples are exhibited in museums, the majority of the species being known from the young stage only, that the collector will find himself amply recompensed by attending to these desiderata.

Scaly fishes are skinned thus: with a strong pair of scissors an incision is made along the median line of the abdomen from the foremost part of the throat, passing on one side of the base of the ventral and anal fins, to the root of the caudal fin, the cut being continued upwards to the back of the tail close to the base of the caudal. The skin of one side of the fish is then severed with the scalpel from the underlying muscles to the median line of the back; the bones which support the dorsal and caudal are cut through, so that these fins remain attached to the skin. The removal of the skin of the opposite side is easy. More difficult is the preparation of the head and scapulary region; the two halves of the scapular arch which have been severed from each other by the first incision are pressed towards the right and left, and the spine is severed behind the head, so that now only the head and shoulder bones remain attached to the skin. These parts have to be cleaned from the inside, all soft parts, the branchial and hyoid apparatus, and all smaller bones, being cut away with the scissors or scraped off with the scalpel. In many fishes, which are provided with a characteristic dental apparatus in the pharynx (Labroids, Cyprinoids), the pharyngeal bones ought to be preserved, and tied with a thread to the specimen. The skin being now prepared so far, its entire inner surface as well as the inner side of the head are rubbed with arsenical soap; cotton-wool, or some other soft material is inserted into any cavities or hollows, and finally a thin layer of the same material is placed between the two flaps of the skin. The specimen is then dried under a slight weight to keep it from shrinking.

The scales of some fishes, as for instance of many kinds of herrings, are so delicate and deciduous that the mere handling causes them to rub off easily. Such fishes may be covered with thin paper (tissue-paper is the best), which is allowed to dry on them before skinning. There is no need for removing the paper before the specimen has reached its destination.

Scaleless Fishes, as Siluroids and Sturgeons, are skinned in the same manner, but the skin can be rolled up over the head; such skins can also be preserved in spirits, in which case the traveller may save to himself the trouble of cleaning the head.

Some Sharks are known to attain to a length of 30 feet, and some Rays to a width of 20 feet. The preservation of such gigantic specimens is much to be recommended, and although the difficulties of preserving fishes increase with their size, the operation is facilitated, because the skins of all Sharks and Rays can easily be preserved in salt and strong brine. Sharks are skinned much in the same way as ordinary fishes. In Rays an incision is made not only from the snout to the end of the fleshy part of the tail, but also a second across the widest part of the body. When the skin is removed from the fish, it is placed into a cask with strong brine mixed with alum, the head occupying the upper part of the cask; this is necessary, because this part is most likely to show signs of decomposition, and therefore most requires supervision. When the preserving fluid has become decidedly weaker from the extracted blood and water, it is thrown away and replaced by fresh brine. After a week’s or fortnight’s soaking the skin is taken out of the cask to allow the fluid to drain off; its inner side is covered with a thin layer of salt, and after being rolled up (the head being inside) it is packed in a cask, the bottom of which is covered with salt; all the interstices and the top are likewise filled with salt. The cask must be perfectly water-tight.

Of all larger examples of which the skin is prepared, the measurements should be taken before skinning so as to guide the taxidermist in stuffing and mounting the specimens.