Fig. 20A WHALE’S MOUTHThe carcass is ready for cutting up at a Shetland whaling station.
Fig. 20A WHALE’S MOUTHThe carcass is ready for cutting up at a Shetland whaling station.
Of the toothed whales, the most important is the Cachalot or Sperm whale. It is chiefly captured inSouthern seas, and is killed in large numbers for the sake of the spermaceti and sperm oil that occur in large quantities in its head cavity. Sperm and other toothed whales feed upon fish and cuttlefish.
The breeding habits and migrations of the different species of whales are at present little understood. During the summer, when the water in the Polar circles swarms with certain varieties of pelagic crustacea, the whales congregate in these regions and are then most profitably hunted. At the end of the summer they appear to migrate towards warmer water nearer the Equator. They bring forth their young in warm, shallow water, and return to the whaling grounds in the spring. A young whale calf may be as much as 20 ft. long at birth.
Whales were captured by the Norwegians over 1,000 years ago. In the Middle Ages—from the ninth to the seventeenth centuries—the Basques hunted the Black whale in the Bay of Biscay, and supplied Europe with oil and whalebone. Towards the end of the sixteenth century, as the Biscay whales became rare and more difficult to find, the whalers ventured further afield, and in 1612 discovered the Greenland whale. The Black or Biscay whale is now almost extinct, and there is every likelihood that the Greenland Right whale will also soon be exterminated. The capture of Sperm and Rorqual whales, although equally important, is a comparatively modern development.
Modern whale fishing has become a very efficient art, owing largely to the invention of the shot-harpoon by a Norwegian, Sven Foyn, in 1870. This harpoon is discharged from a gun from the deck of a fast steamship. It penetrates the body of the whale in the vital region just behind the flipper. The invention of this weapon has made the killing of whales a matter of comparative ease and certainty. The inevitable consequence of thisis that the whales are being killed in such large numbers that they are in danger of general extermination. Even before the introduction of the shot-harpoon, whales were being destroyed at an astonishing rate. Thus, during 40 years in the middle of the last century, over 300,000 whales were captured by the United States whale fisheries alone. The value of these whales was £65,000,000, so that each whale realized on an average £216. Of recent years—before 1914—a single large Greenland whale has realized as much as £900 for whalebone and £300 for oil. At the present time, over 20,000 whales are killed each year.
The old eighteenth century whaler of about 400 tons burden carried about 30 officers and men, and was equipped for a three years’ voyage. Each whaler carried six whale boats. These whaleboats were about 27 ft. long and built sharp at each end. Each boat was furnished with mast and sails, and was provided with two 200-fathom whale lines. When a whale was sighted four of these boats, each manned by six men, started in pursuit. The boats ranged themselves alongside the whale and a harpoon was driven into it from each boat. The whale immediately dived to the bottom of the sea and remained there sometimes for as long as forty minutes. When he returned to the surface to breathe, more harpoons were thrown and he dived again. Ultimately, owing to loss of blood, the whale kept near the surface and was then dispatched by a lance thrust behind the flipper into the vital parts.
The modern Greenland whaler is an iron vessel of about 500 tons. She is fitted with auxiliary engines of 75 horse-power. She carries from fifty to sixty hands and eight whaleboats. She is fitted with tanks for 250 tons of oil. Before the war she would cost about £17,500 to build and £500 a month to maintain. Each whaleboatcarries a harpoon gun in order to make sure of the first harpoon getting a good hold.
In Rorqual fishing, off Newfoundland, the harpoon is tipped with a bomb and time fuse. This explosive harpoon is discharged into the whale from the deck of the whaler—a fast steamer—and explodes with fatal effect.
The chief whale fisheries are carried on off Greenland for the Greenland whale, off the coast of Newfoundland for Rorquals. There is the Norwegian bottlenosed-whale fishery around Iceland, and the American Bowhead-whale fishery in the Behring Sea. In Southern Seas the Humpback, Fin whale, and Blue whale (Sibbald’s Rorqual) constitute an overwhelming majority of the whales captured. The Right whale and the Sperm whale, although captured in relatively small numbers, are individually more valuable. Other smaller species, e.g. the Sei whale (Rudolph’s Rorqual), the lesser Rorqual and the Killer or Grampus, are also found in large numbers in the Antarctic.
When the whale has been killed it is either made fast alongside the whaler and cut up, or it is towed ashore to a “factory” to be cut up and stripped. The blubber is stripped off, cut up into small pieces, and boiled down with water to separate the oil. The yield of oil varies for different species, as shown inTable II. The whalebone is removed and, if a Sperm whale, the oil is removed from the skull cavity with buckets. An average large Sperm whale will yield from 21⁄2to 3 tons of Sperm oil.
TABLE IIAverage Yield of Oil in BarrelsSpecies of Whale.(6 Barrels = 1 Ton).Right60 to 70Blue70 „ 80Fin35 „ 50Sei10 „ 15Humpback25 „ 35Sperm60 „ 65
Whale oil is marketed in five grades: Nos. 0, 1, 2, 3, and 4. Nos. 0 and 1 are made entirely from blubber; No. 2 from tongues and kidney fat and from the residue of the blubber boilings; No. 3 is made from the flesh and bones, and No. 4 from refuse. The different grades contain progressively from1⁄2to 1 per cent water and dirt, and from 2 to 30 per cent free fatty acid.
Grades 0, 1 and 2 of whale oil are used in the manufacture of soap, glycerine being obtained from it as a by-product. In its natural condition the oil is soft, and has to be “hardened” before it can be used for soap making. The hardened whale oil is white, odourless and tasteless, and is an excellent substitute for tallow. In this condition it is also used as a substitute for lard and, to a small extent, is used in making margarine.
Grades 3 and 4 are used in the manufacture of lubricating greases. Whale oil alone is used for shafting and machinery bearings. When mixed with mineral oil, it is used for looms, spindles and textile machinery. Whale oil is also used as an illuminant, for currying leather, and in making chamois leather, for batching flax and other vegetable fibres, and in oiling wool for combing.
In 1913, the world’s annual catch of whale oil had reached 800,000 barrels. During the war the supply was considerably less, for example in 1917 it was only 358,000 barrels.
Whalebone.Whalebone from the mouths of the Right or whaleboned whales is in considerable demand among dressmakers and milliners. Its principal use is in the brush trade, chiefly in making brushes for mechanical purposes. It is prepared for use by being boiled in water for about 12 hours until it is quite soft. It is then cut into strips or bristles or filaments, according to the use for which it is intended. It is light, flexible, tough and fibrous.
Sperm Oil.Sperm oil is really a liquid wax. It is an excellent lubricant—particularly for rapidly moving machinery, e.g. spinning spindles, or for delicate machinery such as watches. It does not become gummy or rancid, and retains its viscosity at high temperatures. It has no corrosive action.
When cooled to low temperatures, it deposits a solid wax—spermaceti—which is used in the manufacture of high grade candles. Sperm oil is also used for dressing leather, in oil tempering steel, and as an illuminant.
Ambergris.Ambergris is a solid, fatty, inflammable substance, dull grey in colour, which occurs as a concretion in the intestines of sperm whales. It is generally found floating in the sea or on the shore. It is used in the perfume industry mixed with other perfumes.
The development of the whaling industry in the south seas has led to the industrial development of previously uninhabited islands. On South Georgia, which was previously uninhabited, actual industrial villages have been established. A church has been erected, and there are three slips for cutting up the whales, two guano factories, reservoirs for the oil, and houses for the staff. This Antarctic island has a floating population of many hundreds of sailors and workmen. A doctor resides there during the whaling season and, since 1908, the British Government has established a post office in this polar land. In 1922 the eyes of all the world were turned to this far-away land, the Gate of the Antarctic, as the body of Sir Ernest Shackleton, the hero of the Antarctic, was laid to rest there.
Thepreservation of fishes for use as food long after they have been caught is a matter of constantly increasing importance to the prosperity of the fishing industry. In most other food supplying industries the produce can be kept fresh for the market comparatively easily. Dry grain will keep indefinitely; vegetables and fruits with proper care will generally remain “fresh” long enough to reach distant markets. Oxen, sheep and pigs may be transported to the market alive, and then slaughtered as required. But a fish as soon as it is taken from the water dies and speedily begins to decay.
Fish, like other foodstuffs, whether animal or vegetable, decays as a result of the growth in it and on it of certain micro-organisms (bacteria, moulds). These micro-organisms swarm in the air and on exposed surfaces all the world over. Generally speaking, they flourish best at ordinary temperatures and in a moist environment.
Foodstuffs can be preserved from decay only by preventing the growth and development of these decay organisms. They can be killed outright by any of the ordinary sterilizing processes such as exposure to sufficient extremes of heat or cold, or by treatment with disinfectant substances (germicides) such as carbolic acid or hypochlorites. Clearly, however, foodstuffs cannot be preserved indefinitely by the simple process of killing all the organisms that are resident on the foodstuff at the time of treatment, for, as soon as the foodstuff is exposed to the air, it will become infected afresh.
They can be preserved—
(1) By boiling, and packing immediately afterwards in air-free containers.
This process is, of course, the basis of the great meat packing industry. The meat is packed in a tin, the tin and its contents are heated in steam or boiling water until the meat is cooked and all the decay organisms are destroyed. The tin is then sealed, air-free and air-tight.
(2) By freezing.
Cold storage is a widely used method of preserving foodstuffs. The low temperature prevents the growth and development of decay organisms and, as long as the foodstuff is kept sufficiently cold, arrests decay.
Prehistoric animals long extinct are sometimes found firmly embedded in the Polar ice, as fresh as they were on the day they were drowned.
It is found that the stability and subsequent quality of frozen meat or fish depend directly upon the manner in which it has been frozen. It may be frozen in air, or when immersed in brine. Of these two methods the latter is much quicker, because brine is over twenty-five times as good a conductor of heat as air is. During the slower air-freezing process the quality of the flesh is impaired by the separation of the contained water into comparatively large crystals of ice. This leads to the displacement of the membrane and tissues of the meat, so that in thawing again the meat drips and becomes tough. When immersed in brine freezing occurs too rapidly for this separation of water to occur to any marked extent.
The keeping qualities of brine-frozen fish also are greater than those of air-frozen fish, owing to the protecting coating of ice which effectively prevents contact with bacteria or mould spores.
(3) By drying.
Primitive man preserved his meat by drying it in thesun, or in the smoke of a fire. To-day the preparation of fish, dried fruits, desiccated vegetables, etc., is a world-wide industry.
Generally speaking, decay organisms can only develop in a moist environment. All fresh foodstuffs contain a large proportion of water. The removal of this water effectively checks decay. Drying alone, however, does not always produce a permanent “cure,” as the foodstuff is always liable to get moist again. For that reason it is customary to combine the drying process with treatment with an antiseptic substance such as salt. Smoke drying is better than sun drying, for although the ultra-violet rays of the direct sunlight effectively kill bacteria and mould spores wood smoke contains antiseptic substances with which the meat becomes impregnated, so that even the chance of any subsequent infection is greatly reduced.
(4) By treating with an antiseptic substance such as salt.
Antiseptic substances differ from disinfectant substances in that they do not kill micro-organisms, but only arrest their development.
As a rule, they are effective preserving agents, and do not make the food poisonous or unpalatable.
All these methods can be, and are, used for preserving fish, the method most commonly used being treatment with salt. Fish, however, are often kept in ice on board during a fishing trip and are then either packed in ice for transit under special storage conditions (if required fresh) or they are salted down.
Methods of Salting.Different methods of salting are used, according to the character of the fish and the locality. The fish are either cleaned (split and gutted) or salted “round” (whole). In general, the method used is one of the following—
(1)Dry-salting.The fish are cleaned, rolled indry salt, and packed in layers in open casks. Each layer of fish is covered with a layer of salt.
(2)Brine Pickling.The fish are immersed in saturated brine, salt being added from day to day to restore the strength of the brine as it becomes weakened by the water which it extracts from the fish.
(3)Kenching.The fish, either split or round, are piled in layers in the hold of the ship, or on the floor of the warehouse, each layer being covered in turn with a layer of salt. The brine, as it forms, is allowed to drain away.
Of all these three methods, the first is undoubtedly more effective, more economical, and requires less attention than the second. The third method is often used on board ship and sometimes on shore as a temporary expedient when the catch is too large for the number of containers available.
In the dry-salt method, the fish are packed tightly in the casks, and are not afterwards disturbed. When cured they possess a characteristic dry, shrunken appearance.
Fish pickled in brine need attention every day. The brine has to be closely watched so that it shall not become too weak. Fresh salt has to be added daily, and the fish stirred up with wooden paddles to ensure uniform pickling.
Fish cured in this way are softer and more plump than those cured by the dry-salting method.
When a fish is packed in salt the salt rapidly extracts water from the flesh and a strong brine results.
The salt dissolves in the remaining flesh juices of the fish, and rapidly diffuses throughout the fish, thoroughly permeating it. By this process, therefore, the fish is partially dried and becomes thoroughly impregnated with salt.
The gradual change in the composition of the flesh is reflected in the following analysis—
Sample.%Water.%NaCl.%Fat.Fresh herring, ungutted67·330·6313·78Herring lightly salted, before gutting66·331·2712·11Herring from rousing tub, gutted and salted, ready to pack into barrel61·091·4116·14Herring, after 7 days salted in barrel52·677·4317·10Herring, after 8 days salted in barrel46·9011·4922·50
Fresh herring, ungutted
Herring lightly salted, before gutting
Herring from rousing tub, gutted and salted, ready to pack into barrel
Herring, after 7 days salted in barrel
Herring, after 8 days salted in barrel
The efficiency of the cure and the appearance of the finished product will be influenced by the following factors—
(a) The temperature—whether summer or winter;(b) The freshness of the fish;(c) The quality of the salt—its purity and grain;(d) The quantity of salt used;(e) The duration of the process.
(a)The Temperature.As soon as a fish is dead, it commences to decay.
In hot weather, decay proceeds more rapidly and the interior portion of the meat may become soured before the salt reaches it. Clearly, if the rate at which the salt penetrates the fish is retarded by the salt being impure, or of too fine a grain, or by the brine being too weak, the probability of the fish being spoilt is very much increased.
The dry salt method leads to a much quicker penetration of the fish than the brine method, and should always be used in warm weather.
(b)The Freshness of the Fish.The decay processes gather impetus day by day. It is clear, therefore,that in order to avoid the possibility of “souring,” the fish should be salted with the least possible delay.
(c)The Quality of the Salt.(1)Its Purity.The impurities commonly present in Fishery Salt are the sulphates and chlorides of calcium and magnesium.
The following analysis show the composition of typical samples of Fishery Salt.
Composition.GermanRockSalt.Italian.Spanish.French.English.%%%%%Salt (Sodium chloride)97·2896·5996·6395·8698·9Calcium chloride—0·32—0·16—Magnesium chloride0·251·190·960·350·08Magnesium sulphate—1·750·73——Sodium sulphate0·44———0·04Sodium bicarbonate0·01————Insoluble (Calcium sulphate, sand, etc.)2·020·151·683·630·98100·00100·00100·00100·00100·00Moisture0·206·544·471·393·25
Salt (Sodium chloride)
Calcium chloride
Magnesium chloride
Magnesium sulphate
Sodium sulphate
Sodium bicarbonate
Insoluble (Calcium sulphate, sand, etc.)
The Spanish and Italian salts are solar salts, obtained by evaporating sea-water by the heat of the sun. Solar salt nearly always contains more magnesium salts than brine salt does. This constitutes a serious disadvantage to the fish curer.
Of the calcium salts which occur as impurities in Fishery Salt, the sulphate is practically insoluble in brine, and is probably without action upon the salting process.
Calcium chloride, on the other hand, resembles magnesium chloride and is an undesirable constituent of Fishery Salt, for calcium chloride, and to a lesser extent magnesium chloride and magnesium sulphate, diminish the rate at which the salt penetrates the fish. Curingwill, therefore, be delayed, and in warm weather (above 70°F.) this may result in the souring of the fish.
To obtain rapid and thorough curing, therefore, it is necessary—especially in warm weather—to use salt which contains as little calcium and magnesium salts as possible.
Pure salt, used dry, produces a soft, yellow-meated fish which is flexible in the hand. Salt containing calcium chloride or magnesium chloride produces a harder and stiffer fish with a markedly whiter colour.
Salted fish can only be stored satisfactorily in a dry place. Fish which has been cured with impure salt is hygroscopic and will run wet in the store.
This hygroscopic moisture weakens the preserving action of the salt. Fish that has been cured with a pure salt will keep much drier under ordinary storage conditions.
(2)Its Grain.The crystals of Fishery Salt should be coarse and hard. Coarse crystals dissolve slowly, and so produce a more gradual cure than fine-grained salt does. Fine-grained salt extracts the water so rapidly from the surface tissues that it coagulates them. This retards the further penetration of the salt into the fish, so that the fish has the appearance of being slack salted.
Round versus Cleaned Fish.The thoroughness with which a cut fish is cleaned and washed influences the temperature at which the fish can be salted successfully, and materially affects the quality and taste of the product. Tressler1has shown that the chief cause of fish spoiling when salted in hot weather is the decomposition of the blood which remains in the flesh. Even in cold weather, it is found that the extra washing and cleaning greatly improve the quality of the fish. As the presence of blood in the fish also leads to discolourationduring the salting process, a thoroughly cleaned and washed fish is, after salting, much whiter in appearance and has a finer taste.
Many fish are skinned before they are salted. It has been observed that a skinned fish will cure almost twice as quickly as an unskinned fish. This is because salt penetrates the meat of the fish at approximately twice the rate at which it penetrates the skin. It is desirable, therefore, particularly in hot climates, to skin the fish before salting. This, of course, is only commercially practicable with certain large kinds of fish such as cod.
The Reddening of Salted Fish.Salted fish sometimes undergo a change, either during the salting process if improperly carried out, or more generally in the store, which is characterized by the development on the surface of the fish of irregular red and brown patches. This reddening occurs not only on the fish, but also on the floors and walls of the curing factories, on the sides and decks of fishing boats, and even on the salt itself. It occurs most readily in warm weather.
The reddening has been shown to be due to the growth of a micro-organism (a micro-coccus). With this micro-coccus are generally associated a bacillus and a micro-fungus which produce the brown mould on the fish.
Fish become infected with these micro-organisms by contact with boats or docks or warehouses.
Every precaution should be taken to keep such places clean and properly disinfected.
The “rusting” of fatty fish, e.g. herring, is due to the oxidation of certain free, fatty acids split off from the fats by enzyme action.
Withfew exceptions, the different species of fishes that are caught industrially are important because of their food value.
Some fishes are unsuitable for food because they have an unattractive taste; others are directly poisonous. Thus, in the Japanese fish of the genus tetrodon, the roe is poisonous, although the remainder of the fish is edible. Some fishes are poisonous during the spawning season. Others are provided with a special poison gland connected with special spines or barbs. In edible fishes, given the suitable conditions, poisons may be formed by bacterial activity in the flesh of the fish. Poisons so formed give rise to the kind of fish poisoning known as botulism. Cases of botulism have resulted from eating canned salmon and sardines that have become spoiled. In some cases, bacteria present in a diseased fish may produce poisonous substances in the body of the fish. Bacillus paratyphosus has been isolated from some poisonous fish, and certain poison-producing bacteria have been found in others.2
Certain shellfish are notoriously liable to be poisonous. The exact nature of the microbes concerned in the production of poisonous substances in shellfish is at present unknown; it is clear, however, that such poisonous substances may be produced in shellfish in three ways—
(1) Microbes of various infectious diseases, such as typhoid fever, may be absorbed by the shellfish from sewage.
(2) The shellfish may be diseased, or be seriously contaminated, by living in dirty water.
(3) Decomposition may set in after the shellfish have been removed from the water—particularly if they have been kept too long in a warm place.
It has been found recently that shellfish that have been deliberately fattened on sewage can be effectively cleansed in such a way as to get rid of ingested sewage bacteria. This process has been carried out successfully on a commercial scale at Conway by the Ministry of Agriculture and Fisheries. Danger from infected shellfish may also be safely avoided by boiling them. When shellfish are gathered at the right season of the year and from suitable localities, they are a perfectly safe and wholesome food.
Of the many species of edible fishes that are known and used, the number is by no means complete, and new species are added from time to time. Thus, in 1916, the United States Bureau of Fisheries introduced a new edible fish (Lopholatilus chamaeleonticeps), which they christened the tile fish. After this fishery had been in existence for twelve months, the known catch of tile fish amounted to over 10,000,000 lbs., valued at more than $400,000. In 1917, the same Bureau introduced the dog-fish under a new name. As people were prejudiced against the name “dog fish,” the Bureau altered it to “gray fish,” “which is descriptive, not preoccupied, and altogether unobjectionable.” The fish is now caught in large numbers, and forms the basis of a very flourishing canning industry. Attempts have been made recently to utilize as food the edible portions of the shark (which is closely related to the dog fish) and the porpoise.
The food value of most fishes varies very much according to the condition of the fish when it is caught—thatis whether it is spawning or not. Further, it may be considerably modified by the changes that take place subsequently in the composition of the flesh during the processes of curing, cooking or preserving.
Generally speaking, all marine fish annually pass through a well-marked series of seasonal changes, the stages of which appear to depend upon changes in the temperature, salinity and alkalinity of the sea. These changes are directly connected with the development of roe and milt, with the fluctuation in the percentage of oil and fat in the liver and body tissues, and also with the rate of growth. Thus the chemical composition of the fish, and hence its food value, varies greatly according to the season at which it is caught.
Norwegian brisling (“Skipper Sardines”) are caught in the summer just before spawning time. At this time the fat content is high; in winter the fat content is low, and the fish possesses small commercial value.
The gradual change in the composition and food value (in calories per pound) of the herring as spawning time approaches is well shown inTable III. (Prof. J. Johnstone, Trans., Liverpool Biolog. Soc., Vol. xxxiii (1919), p. 106.)
TABLE IIIManx Summer Herrings, 1916Composition of the Flesh of the Fish: Monthly MeansDate.Condition.Water.OilandFat.Proteid.Ash.Total.FoodValue.MayEmpty75·02·521·12·3100·91,100JuneFilling66·111·418·62·098·11,806JulyFilling55·821·618·42·398·12,762AugustHalf full48·431·516·52·398·73,608Sept.Full51·925·217·32·697·03,050
The herrings are caught in September when they assemble in shoals for the purpose of spawning. They are thus most easily caught at the time when their food value is at a maximum.
The flesh of clupeoid fish—herrings, sprats, pilchards, sardines—contains a quantity of oil disseminated throughout the flesh in the form of fine globules. From the above table it will be seen that the percentage of oil in the flesh of the herring may be as low as 2·5 per cent in May, and as much as 31·5 per cent in August. In summer the adipose tissue forms two distinct layers, one situated just below the skin, the other being parallel to the first, but separated from it by a layer of muscular tissue. In winter the oil content becomes so small that these layers of adipose tissue disappear. A comparatively small amount of oil is contained in the liver of the fish.
In gadoid fishes, e.g. cod, as well as in skates and rays, the oil is almost entirely confined to the liver. During the summer the liver grows larger and richer in oil, until sometimes the oil amounts to more than half the total weight of the liver. (When cod are caught the livers are removed and kept apart, to be treated subsequently for their oil.) The percentage of oil in the flesh of the cod varies from 0·1 per cent to 1·0 per cent. Unlike that of the herring, therefore, the food value of the flesh of the cod does not fluctuate markedly according to the season.
When fish are dry-salted a certain proportion of the proteins and mineral salts in the flesh is extracted by the brine pickle that is formed. In Russia and Poland, where the greater proportion of salted herrings are consumed, the peasants eat them without further cooking, and also consume the pickle.
A great gain in food value per pound results from theremoval of so much water from the flesh of the fish. Freshly caught cod flesh contains about 80 per cent water and 17 per cent protein; after being dry-salted for export it contains about 25 per cent of water and 55 per cent protein.
Thus, 1 lb. of dry cod is equal in food value to about 3 lbs. of fresh cod. The increased food value of salted fish will be seen from the following analyses—
The Effect of Curing and Drying upon theFood Value of Different FishesFood.Protein.Fat.Carbohydrate.Ash.Water.FoodValue.Cal.per lb.Haddock(fresh)12·00·2—0·951·6232„(smoked)14·90·2—3·457·4286Herring(fresh)14·010·4—1·545·7699„(salted)21·215·4—7·730·9944„(bloater)15·79·6—1·552·0697„(kipper)14·111·1—3·446·9730Sprats(fresh)12·610·7—1·349·4686„(smoked)21·214·9—3·239·41,023
Thus, the food value of salted sprats or herrings per pound is 50 per cent more than that of the same fish when fresh.
The original food value of a fish is generally diminished by the cooking process. The fish may be boiled or broiled for direct consumption, or it may be steam cooked in cans and sealed up for future consumption, as in the canning industry. When oily fishes, such as herrings, are cooked, the oil globules burst and some of the oil is lost, and the food value of the fish becomes correspondingly less. When salted fish is soaked in fresh water before being cooked, some of the gelatin and other coagulable proteins are extracted from the flesh. This loss of protein can be checked either by broiling thefish, when the protein near the surface becomes coagulated and so prevents the loss of protein from the interior of the fish, or by placing the fish that is to be boiled direct into boiling water, and not into the cold water before the heating has begun.
In addition to this diminution of the food content of the fish, the process of cooking, contrary to general expectation, also diminishes slightly its digestibility.
In the canning process the fish to be canned are cleaned (gutted) and boned, and packed into tins, together with the necessary sauce or seasoning. The tins are then closed, a small hole being left temporarily in the lid. The tins are placed on steam-heated racks, and the contents thoroughly cooked. In this way the contents are sterilized as well as cooked, and the air originally present in the tin is all driven out by the steam through the small hole in the lid. This hole is sealed with a spot of solder while the contents of the tin are still at boiling point. The tin and its contents are allowed to cool down, and are dispatched to the store-room. During storage the contents of the sealed tin gradually “mature.” This maturing process may last from six months to ten years. During this period the bones soften, the flesh becomes soft and pasty, and the taste becomes richer. The precise nature of the changes that take place during this maturing process is not fully understood; probably maturing is partly due to the action of certain enzymes in the flesh of the fish, and partly to the slow but continuous chemical action of the various juices present in the tin. Attempts to pickle herrings from the Zuyder Zee have been unsuccessful owing to a lack of the enzyme action that makes other herrings tender when pickled. The enzyme, although present, is apparently rendered inactive by the presence of an anti-enzyme.
The last, but by no means the least, important factor to be considered in estimating the food value of any particular fish is its retail price. The price of the different kinds of fishes is by no means proportional to their individual food values. It is determined primarily by the abundance or otherwise of the available supply of each individual species. Thus, the various pelagic fish—mackerel, herring, sprat—that are easily caught in enormous quantities at certain seasons of the year are by far the most valuable. Of trawl-caught fish, cod and whiting are more plentiful and are, therefore, cheaper than hake, although, again, the cheaper fish has the greater food value.
In some cases certain fish, although fairly abundant, are in poor demand owing to some prejudice on the part of the public, and are generally sold in poorer districts, or to the fried fish trade, at a disproportionately low price, for example skate, dog-fish, angler fish, john dory.
Taste and appearance also contribute to the popularity and, therefore, indirectly to the retail price of fish, such as the sole and the salmon.
In Table IV the present retail prices (Sept., 1921) and the food values of a number of different fishes are compared. From these figures, the actual food value per shillingsworth of each fish has been calculated.
The cheapest fish, therefore, are also those possessing the greatest food value, e.g. the herring in all its forms, dried cod and ling, and mackerel. These compare favourably both in cost and food value with meat, such as beef and mutton.