APPENDIX.
DIRECTIONS FOR COLLECTING AND PRESERVING FISHES.
Whenever practicable fishes ought to be preserved in spirits.
To insure success in preserving specimens the best and strongest spirits should be procured, which, if necessary, can be reduced to the strength required during the journey with water or weaker spirit. Travellers frequently have great difficulties in procuring spirits during their journey, and therefore it is advisable, especially during sea voyages, that the traveller should take a sufficient quantity with him. Pure spirits of wine is best. Methylated spirits may be recommended on account of their cheapness; however, specimens do not keep equally well in this fluid, and very valuable objects, or such as are destined for minute anatomical examination, should always be kept in pure spirits of wine. If the collector has exhausted his supply of spirits he may use arrack, cognac, or rum, provided that the fluids contain a sufficient quantity of alcohol. Generally speaking, spirits which, without being previously heated, can be ignited by a match or taper, may be used for the purposes of conservation. The best method to test the strength of the spirits is the use of a hydrometer. It is immersed in the fluid to be measured, and the deeper it sinks the stronger is the spirit. On its scale the number 0 signifies what is called proof spirit, the lowest degree of strength which can be used for the conservation of fish for any length of time. Spirits, in which specimens are packed permanently, should be from 40 to 60 above proof. If the hydrometers are made of glass they are easily broken, and therefore the traveller had better provide himself with three or four of them, their cost being very trifling. Further, the collector will find a small distilling apparatus very useful. By its means he is able not only to distil weak and deteriorated spirits or any other fluid containing alcohol, but also, in case of necessity, to prepare a small quantity of drinkable spirits.
Of collecting vessels we mention first those which the collector requires for daily use. Most convenient are four-sided boxes made of zinc, 18 in. high, 12 in. broad, and 5 in. wide. They have a round opening at the top of 4 in. diameter, which can be closed by a strong cover of zinc of 5 in. diameter, the cover being screwed into a raised rim round the opening. In order to render the cover air-tight, an indiarubber ring is fixed below its margin. Each of these zinc boxes fits into a wooden case, the lid of which is provided with hinges and fastenings, and which on each side has a handle of leather or rope, so that the box can be easily shifted from one place to another. These boxes are in fact made from the pattern of the ammunition cases used in the British army, and extremely convenient, because a pair can be easily carried strapped over the shoulders of a man or across the back of a mule. The collector requires at least two, still better four or six, of these boxes. All those specimens which are received during the day are deposited in them, in order to allow them to be thoroughly penetrated by the spirit, which must be renewed from time to time. They remain there for some time under the supervision of the collector, and are left in these boxes until they are hardened and fit for final packing. Of course, other more simple vessels can be used and substituted for the collecting boxes. For instance, common earthenware vessels, closed by a cork or an indiarubber covering, provided they have a wide mouth at the top, which can be closed so that the spirit does not evaporate, and which permits of the specimens being inspected at any moment without trouble. Vessels in which the objects are permanently packed for the home journey are zinc boxes of various sizes, closely fitting into wooden cases. Too large a size should be avoided, because the objects themselves may suffer from the superimposed weight, and the risk of injury to the case increases with its size. It should hold no more than 18 cubic feet at most, and what, in accordance with the size of the specimens, has to be added in length should be deducted in depth or breadth. The most convenient cases, but not sufficient for all specimens, are boxes 2 feet in length, 1½ foot broad, and 1 foot deep. The traveller may provide himself with such cases ready made, packing in them other articles which he wants during his journey; or he may find it more convenient to take with him only the zinc plates cut to the several sizes, and join them into boxes when they are actually required. The requisite wooden cases can be procured without much difficulty almost everywhere. No collector should be without the apparatus and materials for soldering, and he should be well acquainted with their use. Also a pair of scissors to cut the zinc plates are useful.
Wooden casks are not suitable for the packing of specimens preserved in spirits, at least not in tropical climates. They should be used in cases of necessity only, or for packing of the largest examples, or for objects preserved in salt or brine.
Very small and delicate specimens should never be packed together with larger ones, but separately, in small bottles.
Mode of preserving.—All fishes, with the exception of very large ones (broad kinds exceeding 3–4 feet in length; eel-like kinds more than 6 feet long), should be preserved in spirits. A deep cut should be made in the abdomen between the pectoral fins, another in front of the vent, and one or two more, according to the length of the fish, along the middle line of the abdomen. These cuts are made partly to remove the fluid and easily decomposing contents of the intestinal tract, partly to allow the spirit quickly to penetrate into the interior. In large fleshy fishes several deep incisions should be made with the scalpel into the thickest parts of the dorsal and caudal muscles, to give ready entrance to the spirits. The specimens are then placed in one of the provisional boxes, in order to extract, by means of the spirit, the water of which fishes contain a large quantity. After a few days (in hot climates after 24 or 48 hours) the specimens are transferred into a second box with stronger spirits, and left therein for several days. A similar third and, in hot climates sometimes a fourth, transfer is necessary. This depends entirely on the condition of the specimens. If, after ten or fourteen days of such treatment the specimens are firm and in good condition, they may be left in the spirits last used until they are finally packed. But if they should be soft, very flexible, and discharge a discoloured bloody mucus, they must be put back in spirits at least 20° over proof. Specimens showing distinct signs of decomposition should be thrown away, as they imperil all other specimens in the same vessel. Neither should any specimen in which decomposition has commenced when found, be received for the collecting boxes, unless it be of a very rare species, when the attempt may be made to preserve it separately in the strongest spirits available. The fresher the specimens to be preserved are, the better is the chance of keeping them in a perfect condition. Specimens which have lost their scales, or are otherwise much injured, should not be kept. Herring-like fishes, and others with deciduous scales, are better wrapped in thin paper or linen before being placed in spirits.
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.
Skeletons of large osseous fishes are as valuable as their skins. To preserve them it is only necessary to remove the soft parts of the abdominal cavity and the larger masses of muscle, the bones being left in their natural continuity. The remaining flesh is allowed to dry on the bones, and can be removed by proper maceration at home. The fins ought to be as carefully attended to as in a skin, and of scaly fishes so much of the external skin ought to be preserved as is necessary for the determination of the species, as otherwise it is generally impossible to determine more than the genus.
A few remarks may be added as regards those Faunæ, which promise most results to the explorer, with some hints as to desirable information on the life and economic value of fishes.
It is surprising to find how small the number is of the freshwater faunæ which may be regarded as well explored; the rivers of Central Europe, the Lower Nile, the lower and middle course of the Ganges, and the lower part of the Amazons are almost the only fresh waters in which collections made without discrimination would not reward the naturalist. The oceanic areas are much better known; yet almost everywhere novel forms can be discovered and new observations made. Most promising and partly quite unknown are the following districts:—the Arctic Ocean, all coasts south of 38° lat. S., the Cape of Good Hope, the Persian Gulf, the coasts of Australia (with the exception of Tasmania, New South Wales, and New Zealand), many of the little-visited groups of Pacific islands, the coasts of north-eastern Asia north of 35° lat. N., and the western coasts of North and South America.
No opportunity should be lost to obtain pelagic forms, especially the young larva-like stages of development abounding on the surface of the open ocean. They can be obtained without difficulty by means of a small narrow meshed net dragged behind the ship. The sac of the net is about 3 feet deep, and fastened to a strong brass-ring 2 or 2½ feet in diameter. The net is suspended by three lines passing into the strong main line. It can only be used when the vessel moves very slowly, its speed not exceeding three knots an hour, or when a current passes the ship whilst at anchor. To keep the net in a vertical position the ring can be weighted at one point of its circumference; and by using heavier weights two or three drag-nets can be used simultaneously at different depths. This kind of fishing should be tried at night as well as day, as many fishes come to the surface only after sunset. The net must not be left long in the water, from 5 to 20 minutes only, as delicate objects would be sure to be destroyed by the force of the water passing through the meshes.
Objects found floating on the surface, as wood, baskets, seaweed, etc., deserve the attention of the travellers, as they are generally surrounded by small fishes or other marine animals.
It is of the greatest importance to note the longitude and latitude at which the objects were collected in the open ocean.
Fishing in great depths by means of the dredge, can be practised only from vessels specially fitted out for the purpose; and the success which attended the “Challenger,” and North American Deep-sea explorations, has developed Deep-sea fishing into such a speciality that the requisite information can be gathered better by consulting the reports of those expeditions than from a general account, such as could be given in the present work.
Fishes offer an extraordinary variety with regard to their habits, growth, etc., so that it is impossible to enumerate in detail the points of interest to which the travellers should pay particular attention. However, the following hints may be useful.
Above all, detailed accounts are desirable of all fishes forming important articles of trade, or capable of becoming more generally useful than they are at present. Therefore, deserving of special attention are the Sturgeons, Gadoids, Thyrsites and Chilodactylus, Salmonoids, Clupeoids. Wherever these fishes are found in sufficient abundance, new sources may be opened to trade.
Exact observations should be made on the fishes the flesh of which is poisonous either constantly or at certain times and certain localities; the cause of the poisonous qualities as well as the nature of the poison should be ascertained. Likewise the poison of fishes provided with special poison-organs requires to be experimentally examined, especially with regard to its effects on other fishes and animals generally.
All observations directed to sex, mode of propagation, and development, will have special interest: thus those relating to secondary sexual characters, hermaphroditism, numeric proportion of the sexes, time of spawning and migration, mode of spawning, construction of nests, care of progeny, change of form during growth, etc.
If the collector is unable to preserve the largest individuals of a species that may come under his observation he should note at least their measurements. There are but few species of fishes of which the limit of growth is known.
The history of Parasitic Fishes is almost unknown, and any observations with regard to their relation to their host as well as to their early life will prove to be valuable; nothing is known of the propagation of fishes even so common as Echeneis and Fierasfer, much less of the parasitic Freshwater Siluroids.
The temperature of the blood of the larger freshwater and marine species should be exactly measured.
Many pelagic and deep-sea fishes are provided with peculiar small round organs of a mother-of-pearl colour, distributed in series along the side of the body, especially along the abdomen. Some zoologists consider these organs as accessory eyes, others (and it appears to us with better reason) as luminous organs. They deserve an accurate microscopic examination made on fresh specimens; and their function should be ascertained from observation of the living fishes, especially also with regard to the question, whether or not the luminosity (if such be their function) is subject to the will of the fish.
Fig. 321.—Scopelus boops, a pelagic fish, with luminous organs.