FISH PRODUCTS
The industrial value and importance of fishes is by no means limited
to their use as food. They yield large quantities of valuable oil. The
fish waste, or offal, chiefly heads, skins, bones and viscera—that
is discarded by the fish curer, is worked up to yield fish glue,
fertilizers and cattle food. The skins of certain large fishes, for
example the shark, are tanned and manufactured into a valuable leather.
The story of the fishing industry would not be complete without a brief
description of the methods by which these products are manufactured.
=Fish Oils.= The various kinds of oil that are obtained from different
species of fish and other marine animals, such as whales and seals, may
be divided into three classes, according to the part of the fish from
which they are extracted.
(1) Fish oils proper are disseminated throughout the flesh of the fish
in the form of fine globules. They are extracted from the entire fish,
e.g. herring, sardine, sprat, menhaden.
(2) Liver oils are located in the fish liver, e.g. cod, shark.
(3) Blubber oils constitute a thick layer of adipose tissue just under
the skin of the marine mammalia, e.g. whale, seal, dolphin, porpoise.
In oily fish, such as herrings and sprats, each minute globule of oil
is enclosed within a thin skin. It is practically impossible to rupture
this skin and liberate the oil simply by the application of pressure.
When, however, these globules are heated the skin shrivels, the oil
globules expand and burst the skin, and the liquid oil is liberated and
can then be extracted from the flesh by pressure. To obtain the oil,
therefore, the fish are boiled or steam heated in large vats until the
oil is set free. The hot mass is then placed in a press and the oil
squeezed out. The residue is made into cattle food and fertilizer.
In obtaining the best sorts of liver oils, e.g. codliver oil, the
livers are taken from the fish as soon as they are caught, and are
heated in steam-jacketed vessels until the cell membranes burst and the
oil exudes. The oil is then separated by pressure.
Inferior qualities of oil are obtained by treating putrid livers in the
same way at the end of the voyage. These tainted liver oils are unfit
for medicinal purposes, but are used in large quantities in the leather
industry.
Blubber (which is from 8 to 20 ins. thick) is stripped from the whale
as soon after capture as possible. Generally the dead whale is made
fast alongside the whaler, a deep, spiral cut is made round its body,
and the blubber is stripped off and hauled aboard. This is then cut
into pieces, chopped up in mincing machines and fed into melting
pans and heated with steam, often under pressure. The oil gradually
exudes and collects upon the water, the cell membranes, etc.—the
greaves—settling to the bottom. At the conclusion of the boil, the oil
is drawn off from above the aqueous (gluey) layer, and is clarified by
straining through sieves or filters. The “greaves” is placed in hair
or woollen bags and submitted to hydraulic pressure, by which means a
further quantity of oil is obtained.
Fish oils, unless specially purified for medicinal purposes, are
dark-coloured liquids, with a characteristic, unpleasant, fishy smell,
due to the presence of small quantities of fishy decomposition
products, for example trimethylamine.
When cooled, many samples of fish oil deposit solid masses of fish
tallow (fish stearine).
Fish oils, and, to a less extent, the marine animal oils, e.g. whale,
seal, porpoise, are drying oils like linseed oil, that is they possess
to a very marked degree a capacity for absorbing oxygen from the air,
and so become thickened and viscous. This thickening is generally
induced by blowing air through the warm oil. Oils that have been
thickened in this way are known as “blown” oils.
Blown fish oils are mixed with mineral oils for use as lubricants for
heavy machinery. They have been used as vehicles for paints in place
of linseed oil, but with somewhat disappointing results. They are used
successfully in place of linseed oil in the manufacture of printers’
ink, and in making paints for painting smoke stacks. Such paints resist
successfully the action of heat and light.
More particularly, they are used in the leather industry. Fish oils are
used chiefly in the manufacture of chamois leather. Ordinary chamois
or wash-leather is made from the flesh-splits of sheep skins. The skin
is well washed and softened, and freed from hair by treatment with
lime. It is then split, and the loose and fatty middle layer removed
by a sharp knife. The lime is removed by a short bran-drench and the
superfluous moisture is pressed out. The skin is thus rendered porous
and easily able to absorb the oil. It is stretched on a table and oiled
with fish or whale oil. The oiled skin is folded up and worked for two
or three hours in the faller stocks and then shaken out and hung up
for a short time to cool and partially dry. The process is repeated a
number of times, until all the water originally present in the skin
has been replaced by oil. The oiled skins are then piled in a warm
place. The oil gradually oxidizes—probably owing to some fermentation
process—and the skins become yellow and very hot. From time to time the
skins are strewn on the floor to cool and then re-piled, the process
being repeated until the oxidation of the oil is complete. In France
the freshly-oiled skins are hung in hot stoves, and the oxidation of
the oil is completed in one operation.
The skins are then dipped in water and passed through hydraulic
presses, by which the surplus oil is removed. This surplus thick,
oxidized oil is known as “degras” or “moellon,” and is used for
stuffing leathers that have already been tanned. Stuffed leathers are
supple and impervious to water, and are used for harness, belting,
etc. A further quantity of oil may be removed from the “chamoised”
leather by treating it with potash or carbonate of soda, “sod” oil
being recovered from the extract by neutralization with sulphuric acid.
The value of sod oil for oiling dressed leather is due to a resinous
acid of unknown composition, that is soluble in alkali but insoluble in
petroleum ether.
Enamel or patent leather is generally coated, after tanning, with
a linseed oil varnish, boiled with prussian blue, and dried in a
steam heated chest at 70° to 80°C., the process being repeated
until a sufficiently thick coat is produced. Fish oils are now used
successfully in place of linseed oil. The enamel leather produced,
although not quite so glossy as that made with linseed oil, is said to
be more pliable.
Fish oils are also employed in the manufacture of such closely-related,
although happily diverse, substances as soap and margarine. All
animal and vegetable fats and oils are essentially compounds of
glycerine, with one or other of three acids: palmitic, stearic and
oleic. Palmitic and stearic acids and their compounds are solids at
the ordinary temperature, whereas oleic acid and its compounds are
liquid. This difference appears to be connected in some way with the
molecular structure of these substances. When oleic acid is heated
with hydrogen gas under pressure, in the presence of finely-divided
nickel, it absorbs hydrogen and is transformed into stearic acid. Oleic
acid, therefore, is said to be unsaturated with respect to hydrogen,
whereas stearic acid is called a saturated acid. This process, whereby
a liquid oil is transformed into a solid fat, is called hydrogenation,
or hardening.
Both the margarine industry and the soap industry require large
quantities of hard fats. Originally the soap industry absorbed the
available supplies of hard animal fats such as beef suet, hog’s lard,
and mutton suet. The margarine industry depended upon these same
supplies of animal fats, and the rapid growth in the production of
margarine during recent years has seriously diminished the supply of
hard fats necessary for the manufacture of soap.
The hydrogenation of whale oil and various fish oils has now made
it possible to supply this demand, and has also made possible the
industrial utilization of substances, such as fish oils, for which
formerly comparatively little use could be found.
Hardened whale oil melts at 40° to 50°C., and is a white solid entirely
devoid of taste or smell. It is used for making soap, and as a lard
substitute for cooking purposes.
=Fish Glue.= Fish glue is the most important liquid glue on the market.
The bulk of the fish glue manufactured to-day is made from the waste
and offal that are discarded by the curers. This waste consists of
heads, bones, viscera and skins. The best glue is obtained from the
skins of non-oily, demersal fish, for example cod, haddock, soles,
plaice and hake.
The waste is washed in running water to free it from salt. Sometimes
the waste—particularly the heads—is decomposed with hydrochloric
acid and afterwards neutralized with lime. It is then charged into a
cooker provided with a perforated, false bottom. The stock is covered
with water and heated with steam. The glue is extracted and gradually
concentrates in the water. When this glue liquor is sufficiently
concentrated (from 5 to 6 per cent), it is run off (the first run) and
more water is added to the waste and the cooking continued. After about
10 hours cooking, nearly all the glue has been extracted and the liquor
is again run off (the second run). The cooked waste is then withdrawn,
and any remaining glue liquor is pressed out of it and added to the
second run. From 2 to 4 per cent of phenol or boric acid are added to
prevent decomposition by bacteria.
The glue liquor is evaporated down to a concentration of 32 per cent in
open vats or closed evaporators, and is bleached with sulphurous acid.
A small amount of some essential oil, e.g. cassia, clove, wintergreen,
is added to check mould growth and mask the fishy odour. Glue is also
made in a similar way from the “greaves” obtained from whale blubber.
Fish glue is manufactured in three grades.
GRADE I is made from skins, only the first run being used. It is used
for photo-engraving work, for the production of half-tone plates.
GRADE II is made from second run skin liquors and fish waste. It is
sold in small cans and bottles for general repair work.
GRADE III is prepared from fish heads, and is sold in large cans and
barrels for sizing, box making, cabinet making, and general joiner
work.
The glue is sometimes made more flexible by the addition of glycerine
and glucose. The flexibility of fish glue makes it useful for the
manufacture of court plaster, labels, stamps, and in book-binding.
The residue from the press is dried and sold as chicken feed or
fertilizer. For the latter purpose it is frequently mixed with
Carnallite.
=Fish Gelatine.= Fish gelatine or isinglass is obtained from the
swimming bladder of the sturgeon and also of the cod. The bladders are
exported, either opened (pipe isinglass) or washed, split open and
dried (purse, lump or leaf isinglass).
Isinglass is the purified and dried inner skin of the bladder. It has
but feeble adhesive power. It is used for clarifying wines, ciders and
beers, and for making jellies and plasters.
=Fertilizers.= In many places near the sea, fish are employed whole as
manure. Sprats particularly are caught in large numbers and distributed
over the fields, and left to decompose. Fresh sprats contain 63·7 per
cent of water, 1·94 per cent nitrogen, 2·1 per cent ash (0·43 potash
and 0·90 phosphoric acid).
Fish guano or fish manure is generally prepared from the fish waste
discarded by the curer. An average sample of this manufactured fish
manure will contain 12 per cent water, 60 per cent organic matter,
yielding 10 per cent ammonia, 16 per cent of calcium phosphate, and a
residue of salt, sand, magnesia and potash, the amount of potash being
inconsiderable. Fish guano is mainly valuable as a source of ammonia,
the ammonia content ranging from 6 to 11 per cent, according to the
kind of fish used and its previous history, e.g. whether fresh or
salted.
In many places, such as London, the fish offal from the shops and
restaurants is collected, dried and ground up for use as manure.
In Germany in 1918 herrings’ heads were removed by the curers to be
utilized for the production of oil, albumen, and phosphate of lime.
The herring meal contained up to 50 per cent of albumen and calcium
phosphate, the latter being obtained from the bones and heads. The
albumen was extracted chemically and prepared for human consumption.
The oil was extracted with benzol or other solvents, and, after
hardening, was used in the manufacture of butter substitutes. Fish
waste or offal is fed into a continuous cooker. This cooker consists
essentially of a long, cylindrical vessel, through which runs a hollow
steel shaft on which are mounted perforated radial vanes in such a way
that the whole arrangement forms a spiral conveyor. By means of the
hollow shaft and vanes, steam is blown into the mass of fish waste as
it travels slowly through the vessel, so that it is completely cooked
and disintegrated by the time that it emerges at the other end.
The cooked mass is then fed into a press in which a screw conveyor
urges it through a gradually tapering cylinder with perforated sides.
In this way the oil is extracted from it, and it is then dried and
disintegrated by a rotary drier.
There is always a little residual oil in fish manure that tends to
delay its decomposition in the soil. It is important, therefore, that
the oil be removed as completely as possible.
Dry fish manure requires careful storing, as the presence of this small
amount of oxidizable oil tends to promote spontaneous combustion.
In addition to its value as a fertilizer, the high content of protein
(albumen)—namely, 50 per cent—makes fish meal a suitable food for
live-stock and poultry.
The commercial importance of this industry will be realized when we
remember that practically half of the total catch of fish in the world
is discarded by the curers as waste.
=Fish Leather.= The hides of such marine mammals as the walrus and the
seal have long formed the basis of a regular tanning industry.
Of recent years, however, particularly in America, successful attempts
have been made to tan the skins of certain fish, notably the shark. The
skins are treated with alkali to remove fat and oil, the alkali is then
neutralized with acid, after which the skins are washed and tanned. The
leather is said to be soft and pliable, and well adapted for many uses.
Shark skins are also tanned hard, and used to print a grain on
imitation pigskin.
Shark fishing was commenced off the American coast in October, 1918.
The fish are hunted from fast, powerful motor boats, with specially
constructed nets. A small shark 5 ft. long will yield a hide 10 sq. ft.
in area.
Shark skin is naturally very tough and durable, and in its untanned
condition is used by jewellers as a natural emery paper for grinding
and polishing metal surfaces. It is also used as an abrasive in working
hard woods and ivory.
A method has been devised by which a shark skin can be split into
three. The first split, after tanning, is strong and thick, and
suitable for high grade, heavy shoes. The second furnishes leather
suitable for second grade foot wear, and the third resembles suede and
is used in making fancy articles. In addition to the shark’s skin,
the fins, blood, teeth, flesh, and oil of the fish are also utilized
commercially and yield a satisfactory profit.
INDEX
Ambergris, 106
Anadromous fish, 38
Angler (devil) fish, 18, 32
Beam trawl, 46, 77, 86
Berried lobsters, etc., 35
Bivalve, 94
Black (southern right) whale, 100, 102
Bloater, 60, 66
Blue whale, 104
Brill, 24, 31, 78
Brine pickling, 5, 110
Cachalot (sperm) whale, 100, 104
Canning of fish, 92, 93, 108, 120
Capelan, 70, 100
Cast net, 52
Cat-fish, 16
Clams, 73
Cockle, 25, 27, 53, 74, 90, 93
Cod, 2, 19, 21, 22, 30, 31, 32, 34, 37, 43, 48, 69, 78, 86, 89
—— fishing, 69-76
—— liver oil, 69, 76
Cold storage, 108
Cooking of fish, 122
Copepoda, 27, 30, 36, 90
Crab, 25, 35, 52, 90
Cran, 58, 64
Crustacea, 25, 27, 30, 31, 36, 90, 102
Cutter, 77
Demersal fish, 19, 21, 31, 89
Diatom, 28, 90, 96
Distribution of fishes, 18-27
Dog-fish, 31, 32, 34, 35, 116
—— whelk, 94, 96
Dolphin, 24
Dory fishing, 70
Drifter, 10, 50, 56
Drifting, 50, 56-8, 88
Drift net, 50, 56, 77
Drying of fish, 75, 108
Eel, 16, 38, 44
Eggs of fishes, 27, 28, 32, 34, 35, 69, 90
Fin whale, 104
Fish fertilizer, 4, 62, 76, 130
—— glue, 4, 76, 128
—— hatching, 3, 4, 92
—— leather, 4, 132
—— meal, 4
—— oil, 4, 76, 124-8
Fishery salt, 112-114
Fishing grounds, 10, 30, 69, 80-81, 83
—— traps, 42
—— weirs, 42
Fixed engines, 43
Flake drying, 75
Flounder, 16, 19, 22, 32, 39
Food of fishes, 25, 27, 30, 31, 69, 94
—— value of fish, 37, 54, 115
Gills, 16, 24, 25, 31, 94, 95
Grampus whale, 24, 104
Grayfish, 116
Greenland (Arctic right) whale, 99, 102
Gutting fish, 72, 113
Haddock, 2, 19, 22, 31, 32, 34, 37, 48, 70, 78, 86, 119
Hake, 22, 31, 70, 78
Halibut, 22, 48, 89
Harpoon, 42, 102, 104
Herring, 19, 24, 27, 30, 31, 32, 34, 36, 37, 50, 54, 55, 70, 74, 89,
91, 100, 111, 117, 119
—— fishing, 5, 9, 14, 48, 50, 54, 60, 67, 68, 88
Hose net, 44
Humpback whale, 104
Ice, 83
Immature fish, 3, 52, 86, 88
Incubation period of fish eggs, 35
Inshore fisheries, 11-13, 15, 50
Isinglass, 69, 130
Jelly fish, 28, 30, 77
Katadromous fish, 38
Kenching, 72, 110
Kipper, 60, 66
Larvae of fishes, 27, 30, 34, 35, 36, 38, 91
”Last” of herrings, 58
Limpet, 94
Line fishing, 42, 43, 70-72, 73, 74, 78
Ling, 22, 31, 32, 78
Littoral fishes, 21
Lobster, 25, 35, 52, 90-92
Lobster pots (creels), 42, 91
Mackerel, 18, 25, 27, 30, 31, 39, 44, 50, 89
Mesh of nets, 47, 52, 86, 88
Migration of fishes, 36-40
Mollusca, 25, 27, 30, 31, 36, 90, 93, 94
Mullet, 19
Mussel, 25, 27, 35, 53, 90, 93, 97-98
Nets, 43
Otter trawl, 48, 81
Overday herrings, 60, 66
Overfishing, 3, 11, 80, 84, 86, 91, 96
Oyster, 25, 27, 35, 90, 93, 94-97
—— culture, 95-97
Pelagic fishes, 24, 30, 31, 89
Periwinkle, 25, 35, 53, 94
Phosphorescence, 18, 40, 41
Pilchard, 25, 31, 44
Plaice, 2, 16, 19, 22, 25, 30, 32, 34, 35, 36, 37, 38, 44, 46, 48,
78, 86, 89
Plankton, 24, 27, 28-31, 33, 35, 36, 40, 69, 90, 94, 100
Poke net, 44
Porpoise, 24, 99
Prawn, 25, 30, 35, 90
Preservation of fish, 15, 107 (_See also_ canning, drying, salting.)
Productivity of the sea, 28
Purse net, 44
—— seine, 44
Push net, 52
Red herring, 60, 64
Reddening of salted fish, 114
Reproduction of fishes, 32, 95, 102
Rorqual whale, 100, 102, 104
Salmon, 19, 31, 38
Salt herring, 60
Salting of fish, 5, 6, 62-64, 72, 74, 109
Seal, 99
Sei whale, 104
Seine, 44
Shad, 4, 19, 38
Shark, 4, 16, 19, 24, 32, 34, 43, 132
Shellfish, 90-99
Shrimp, 25, 30, 35, 52, 86, 90, 92, 93
Skate (ray), 6, 22, 24, 32, 34, 78
Skin of fishes, 4, 16, 132
Smack, 9, 46, 77
Smoking of fish, 64, 65, 66
Sole, 2, 16, 19, 22, 31, 32, 78, 86, 89
Spawning of fishes, 19, 24, 32, 34, 35, 37, 38, 39, 50, 54-55, 90,
95, 117
Spermaceti, 102, 106
Sperm oil, 102, 104, 106
Sperm whale, 100, 104
Sprat, 25, 27, 50, 91, 119
Squid, 70
Stake net, 43
Starfish, 50, 96
Steam fishing, 9, 78, 80, 84
Steam trawler, 10, 77, 81
Stickleback, 19, 35
Sturgeon, 16
Tile fish, 116
Trawl (line fishing), 71
—— net (_See_ beam trawl, otter trawl.)
—— —— (shrimps), 2, 52, 93
Trawling, 2, 3, 9, 10, 46, 77-89
—— for herrings, 88-89
Tunny, 24
Turbot, 24, 31, 32, 78, 89
Univalve, 94
Vitamins, 123
Walrus, 99
War service of fishermen, 84
Whale, 24, 99
—— bone, 100, 102, 103, 104, 105
—— fisheries, 99
—— oil (blubber), 103, 104, 105
Whaler, 103
Whaling, 103
Whelk, 94
Whiting, 22, 31, 34, 52, 78, 86
_Printed in Bath, England, by Sir Isaac Pitman & Sons, Ltd._