This note summarizes the main ways in which fish is handled, processed and distributed in Britain, both at sea and on shore. It is principally written for those concerned in industrial training; more detailed information on particular aspects of fish handling and processing is given in other notes in this series, and the reader is referred to some of these where appropriate. The principles and practice of handling and processing are dealt with at length in the book Fish Handling and Processing, Second Edition edited by G. H. O. Burgess and others, and published by HMSO 1965, price £2.
The topics outlined in this note include the handling of wet fish, smoked fish, frozen fish, dried and salted fish, canned fish and shellfish, and the manufacture of fish meal and other byproducts.
Much of the fish landed in Britain is preserved by chilling in ice from the time it is caught until it reaches the consumer. Fish preserved in this way is known as wet fish. A growing proportion of the catch is frozen at sea immediately after capture, and considerable amounts of iced fish are frozen at the ports after landing; these operations are described under freezing and cold storage.
HANDLING WET FISH AT SEA
The length of voyage of fishing vessels storing the catch in ice may range from a few hours for small inshore vessels to about three weeks for the largest distant water trawlers. White fish, that is those species in which most of the fat is in the liver and the flesh is lean, are handled in much the same way on all sizes of vessel. The catch is released from the net on to the deck, gutted immediately, washed, and stowed with ice in boxes or compartments below deck.
Gutting of round fish like cod, haddock and whiting means slitting the belly from throat to vent, removing the liver and cutting out the guts to leave the belly cavity empty. This operation is traditionally done by hand with a knife, but gutting machines are coming into use on both large and small ships to make the task of the fisherman easier. Gutting helps to preserve the fish by removing the main source of spoilage bacteria and digestive juices which attack the flesh of the fish after death. On the larger fishing vessels the livers are cooked in steam boilers to extract the liver oil, but on small boats the livers are discarded with other offal.
The gutted fish are washed to remove traces of blood and debris, and to wash away most of the bacteria present on the skin and in the gills of the fish. The washing equipment on small boats may be simply a hose and an open mesh basket, but on large trawlers a more sophisticated washing tank with circulating water is in general use. In these washers the fish are discharged over a weir and down a chute to the fishroom below deck.
Fishrooms for iced fish are mainly of two types, either an undivided hold in which the catch is stowed in boxes, or a hold divided by partitions into a number of sections called pounds in which the catch is stowed on portable shelves. The principle of stowage is the same; the fish are in shallow layers completely surrounded by ice, whether on a shelf or in a box, so that they are cooled rapidly to ice temperature and kept close to 0°C throughout the voyage. About one part of ice to three parts of fish by weight is required to protect fish for up to 5 days; one part of ice to two of fish is needed for longer voyages. White fish, promptly gutted, washed, and stowed in ample ice, will keep in first class condition for 5-6 days, become stale after 10-12 days, and are unlikely to be edible after 15-16 days.
Boxed stowage is usual on smaller fishing vessels, and the practice of boxing is gradually being extended to larger ships, since the method has a number of advantages including delivery of the fish to the merchant undisturbed by rehandling at the port market, ease of identification of size, species and time in ice, and avoidance of damage and loss of weight during stowage.
Ice plants, particularly older ones at the larger ports, supply crushed block ice to fishing vessels, but more recently built plants, particularly at smaller ports where ice was not locally available in the past, usually deliver small, smooth pieces of ice known as flake ice. Flake ice is normally bulkier than crushed block ice, but weight for weight the cooling capacity of all types of ice, made by any method and from hard or soft fresh water, is the same.
The fish are cooled when heat is absorbed by the surrounding ice, which is thus melted. Further cooling is obtained when the cold meltwater trickles down between the fish. The fishroom temperature is ideally kept slightly above 0°C in order to allow the ice to melt slowly, but is not kept so high as to waste the ice. To this end, most fishrooms on large vessels are completely insulated, and fishrooms on small boats often have partial insulation. Mechanical refrigeration plants are installed on one or two inshore vessels and on some, but by no means all, larger ones; their main purpose is to conserve ice on the outward voyage, and to keep the fishroom air cool during fishing; they have little or no direct effect on the stowed fish, which depend for cooling almost entirely on the surrounding ice.
Fatty fish, like herring, sprats, mackerel and pilchards, i.e. those containing a good deal of fat or oil, are not normally gutted at sea because their small size and the large numbers in which they are caught make this impracticable in the time available on typically short voyages to grounds not far from the port of landing. They are usually put below straight from the net, and iced in boxes. The keeping time of fatty fish in ice is much less than for white fish; the attack by bacteria and digestive juices is much more rapid because the fish are ungutted, and the fat absorbs oxygen to produce rancid flavours and odours. Herring for example are normally required to be in the hands of the port processors within 1-2 days after catching to give a first class product, although for some outlets it is possible to keep herring with a low fat content for 4-5 days in ice. Stowage at sea in refrigerated sea water is a possible alternative to ice as a means of rapidly cooling large quantities of small fatty fish, although the method is not yet in general use in the UK.
The following Advisory Notes, expand the information on handling wet fish at sea: 4 Take care of your catch; 7 The protection of wood in fishrooms, by J. J. Waterman; 11 Handling inshore fish, by J. J. Waterman; 15 Bulking, shelfing or boxing? by J. J. Waterman; 21 Which kind of ice is best? by J. J. Waterman; 32 Superchilling, by J. J. Waterman and D. H. Taylor; 33 The cod, by J. J. Waterman; 42 Fish for caterers and friers, by J. C. Early and R. Malton; 44 Handling fish before canning, by R. McLay; 47 Handling and processing saithe, by J. G. M. Smith and R. Hardy.
HANDLING WET FISH ON SHORE
The catches of British fishing vessels are normally auctioned to fish processing firms at the fishing ports. Most of the large ports are on the east coast, including the three biggest. Hull, Grimsby and Aberdeen. Covered quayside markets are provided at almost all the ports, and merchants’ premises are usually adjacent to, or a short distance from, the markets. At a few remote landing places, particularly on the west coast of Scotland, where no local processing facilities are available, the catches are discharged and consigned by road to the processing centres on the east coast.
Comparatively small amounts of white fish are dispatched unprocessed, repacked in fresh ice, to inland destinations but most white fish is filleted in premises at, the port. Although machines are available for filleting most species, a large proportion of the catch, particularly when handled by the smaller processing firms, is still filleted by hand. The fillets, which constitute roughly 40-50 per cent by weight of the gutted whole fish, are either packed in ice in non-returnable boxes and sent to inland wholesalers and retailers, or are further processed at the port, mainly by smoking or freezing, or both.
A high proportion of the herring catch goes to the kipper trade, and herring for this outlet is split or filleted by machine for making kippers and kipper fillets respectively.
The traditional container for inland carriage of fillets has been the non-returnable wooden box, mainly in units of 7 and 14 lb, but this has been superseded in many large firms by a waterproof fibreboard box and, to a lesser extent, by an expanded polystyrene box, which has some advantage as an insulated container but is more susceptible to damage due to rough handling during transit. Fillets should be kept close to 0°C during transit, and in good practice the fillets are packed in thin layers with ice top and bottom and a little more ice sprinkled among the fish.
Fish is nowadays mostly carried by road transport from the ports and the biggest companies have their own fleets of insulated and refrigerated vehicles carrying fish either to inland distribution depots or direct to customers, while many smaller merchants at the ports share a long-distance transport pool. Although the better carriers use vehicles with adequate insulation, often supplemented by mechanical cooling units, some fish is still carried under less satisfactory conditions on open lorries; much greater reliance has then to be placed on ice and on the insulating properties of the boxes to protect the contents during distribution. Under the best conditions, wet fish can be on sale to the consumer anywhere in Britain within twenty four hours of landing; a typical timetable would be discharge from the fishing vessel in the early hours of the morning, sale to the port merchant and a short journey to his premises at about 8 am, filleting, packing and icing by midday and dispatch by road from the port in the afternoon to arrive at an inland depot in the early hours of the next day, from where it is delivered to the retail shops in time for that day’s trading.
Most retailers keep the bulk of their supplies in chillrooms on the premises and only display a selection on ice, often in refrigerated cabinets.
The following Advisory Notes expand the information on handling wet fish on shore: 1 The care of the fishmongers fish, by G. H. O. Burgess; 3 The handling of wet fish during distribution;, 10 Fishworking premises - materials and design, by J. J. Waterman; 12 Fish display in retail shops; 16 Non-returnable fish boxes, by J. Wignall; 17 Measures, stowage rates and yields of fishery products, by J. J. Waterman; 23 Control of flies in fishmongers’ shops; 42 Fish for caterers and friers, by J. C. Early and R. Malton; 45 Cleaning in the fish industry, by I. N. Tatterson and M. L. Windsor.
Fish is smoked nowadays mainly to give it a pleasant flavour rather than to preserve it. Present day products are therefore only lightly salted and smoked and will not remain edible for much more than a week at ordinary temperatures. The smoking process consists of passing wood smoke over the surface of the fish, in a kiln. Most British products are cold smoked, that is the fish remains uncooked and the kiln temperature does not rise above 30°C. Typical smoked products are the finnan haddock, smoked cod fillet, the golden cutlet and the kipper. Fish that are hot smoked are cooked during the process; the kiln temperature may be as high as 80°C and the fish temperature may reach 60°C. Some hot smoked products in this country are sprats, eels, trout, buckling made from herring, and Arbroath smokies made from small haddocks.
Two types of smoking kiln are in general use, the traditional chimney kiln and the Torry mechanical kiln. It is estimated that more than half of the smoked fish made in Britain is now produced in mechanical kilns, and the proportion is continually increasing.
Before smoking, the fish are immersed in a brine solution. This assists in removing some of the water in the fish, thus tending to firm the flesh. The salt imparts a flavour to the product, but concentration and purity of the salt are extremely important and require to be carefully controlled. A 70 to 80 per cent saturated brine is used in most modern smoke cures.
Fig. 1. A traditional kiln
Following the salting treatment, pre-drying of the fish is required in order to remove some of the moisture prior to smoking. For this purpose, the fish are hung to drip on open racks.
The source of smoke is almost universally a smouldering fire of hardwood chips and sawdust; although more sophisticated smoke producers have been made from time to time, and are used for smoking other foods, these have so far made little impact on the fish trade. In the traditional chimney kiln, the open fires are at the base of a tall, brick-built structure in which the fish are hung on rails of various types called banjoes, speats or tenters, and thus exposed to the rising smoke and warm air. The repositioning of the fish during smoking and eventual removal of the finished products are slow hand operations which require the services of a skilled craftsman in order to produce a satisfactory article.
In the mechanical kiln, the fires are contained in separate fireboxes, and the smoke is blown horizontally through trolleys holding fish in the kiln; the fish may be hung on rails or laid on trays, either of which are supported in the trolley. The temperature and speed of the mixture of smoke and air is carefully controlled to give a uniform product throughout the kiln in a much shorter time than is possible in the chimney kiln. Fish handling is much reduced using the mechanical kiln which can also readily be incorporated in the factory production line. Partial drying as well as smoke deposition is an essential part of the smoke curing process; typically a kipper which should lose about 14 per cent in weight during smoking will require 6-12 hours in a traditional kiln, but only 4 hours in a mechanical one.
Most cold smoked fish products are only lightly coloured by the smoke, and so a permitted dye is normally added to the brine bath through which the fish pass before going into the kiln, in order to enhance the appearance of the finished product.
Fig. 2. A Torry mechanical kiln
The following Advisory Notes expand the information given on smoked fish: 5 Recommendations for the preparation of smoked salmon, by A. Bannerman and J. Horne; 9 Smoked white fish - recommended practice for producers; 14 Smoked fish - recommended practice for retailers; 37 Catching, handling and processing eels, by J. Horne and K. Birnie; 48 Kippers, by A. McK. Bannerman.
Detailed advice on the design and operation of mechanical kilns is given in: Fish smoking, a Torry kiln operator’s handbook, by G. H. O. Burgess and A. McK. Bannerman, published by HMSO 1963.
It is perfectly feasible to keep fresh fish for many months without perceptible change in the eating quality by rapidly freezing it soon after catching and then storing it at a suitably low and constant temperature. With this method of preservation, the thawed product is virtually indistinguishable from the best fresh fish. Freezing has revolutionized the fish processing industry in Britain since the Second World War.
FREEZING FISH
Heat is removed from the fish in the freezing process either by surrounding the fish with a stream of cold air, by placing the fish in contact with a cold surface or by spraying with certain liquid refrigerants. Three main types of freezing plant are used that employ these techniques, the air blast freezer, the plate freezer and the immersion freezer.
The air blast freezer is essentially a tunnel in which a fast-moving stream of very cold air is blown over the fish, which are placed on trolleys or on a moving belt. The air is usually at a temperature of -30 to -40°C and moving at about 5 m/s. The air blast freezer is most suitable for a wide range of sizes of fish, and for products of irregular shape.
The plate freezer is more compact than the air blast freezer, and is most useful for handling fish products that are uniform in thickness and that have a reasonably flat surface which can make good contact with the cold plates. Two versions of the plate freezer are in general commercial use, the horizontal and the vertical types. The horizontal plate freezer, used mainly in land installations, handles many of the catering and retail fish products that are already packed in cartons prior to freezing. Trays of packs are slid between pairs of horizontal plates, the plates are closed tightly on to the packs by hydraulic pressure to make good contact, and a cold refrigerant is circulated through serpentine passages within the plates; a retail pack 3 cm thick takes about an hour to freeze.
The vertical plate freezer, which was originally designed in the 1950s for use on fishing vessels, is employed for freezing large blocks of whole fish. The fish are packed between pairs of plates, usually without any wrappings, and the plates moved slightly towards each other to compact the block and ensure good contact. Liquid refrigerant is circulated through the serpentine passages within the plates until the fish are frozen; the complete process for a block of whole cod 10 cm thick takes about 4 hours including loading and unloading time, with refrigerant at -40°C.
Fig. 3. A horizontal plate freezer
The immersion freezer is not used as much as the plate and blast freezers in the British fish industry; the main difficulty is the limited choice of liquids that are both good refrigerants and suitable for use in direct contact with foods. Brines are sometimes used, but the fish may take up too much salt. Liquid nitrogen is used successfully in one type of immersion freezer, which subjects the product to a spray of liquid nitrogen as it passes through a tunnel.
The freezing process cannot improve the quality of fish; therefore the best frozen products are those made from first class raw material. This applies particularly to whole fish which, after thawing, are likely to be subjected to further processing. Whole iced cod, for example, when frozen not later than 3 days after catching can on thawing be treated in the same way as very fresh fish, but cod that has been delayed longer than this, or has been kept uniced, is unlikely after freezing and thawing to yield fillets of a high quality. Whilst some species, flatfish for example, can be kept in ice a little longer than cod before freezing without impairing the quality of the thawed product, others like haddock and hake do not keep so well. Fillets of most white fish species can be taken from whole fish 5-6 days in ice and frozen to give a high quality thawed product.
The freezing process should always be completed as rapidly as possible, not only to increase output of the equipment, but also to reduce the time in which bacteria and digestive juices are still able to attack the fish; bacterial action ceases below about -10°C, and the activity of enzymes is reduced as the temperature falls. There are marked changes in texture and flavour when fish is frozen very slowly at temperatures only a little below 0°C. The final temperature of fish being frozen should be that at which it is to be stored, namely -30°C; this ensures that the frozen product imposes no extra heat load on the cold store since this is designed only to keep the product cold and not to freeze it.
FREEZING AT SEA
On freezer trawlers handling whole fish, the catch is brought in over the stern, discharged to an enclosed processing deck, gutted by hand or machine, washed and bled in cold sea water and conveyed forward to the freezers, where blocks of about 50 kg are produced in vertical plate freezers and transferred to cold storage rooms running at -30°C. These ships make voyages of 4-8 weeks, carry a crew only two or three more in number than their counterparts handling iced fish, and bring back about 500 tonnes of frozen cargo for transfer to shore cold stores at the ports.
Factory trawlers that fillet the catch before freezing are less numerous than trawlers which freeze whole fish. On the former the gutted fish are filleted mainly by machine, then the fillets are packed into blocks of about 10-15 kg and frozen in horizontal plate freezers before being transferred to the ship’s cold store. Compared to the situation with a trawler freezing whole fish, the crew has to be larger to cope with factory operation at sea, and the quality of fillets frozen at sea as opposed to whole fish frozen at sea depends much more on careful handling and processing, but on the other hand the storage capacity of the ship in terms of frozen edible portion is considerably increased.
It is likely that the distant water fishing fleet will gradually change over completely from the stowage of wet fish in ice to the freezing of fish at sea.
COLD STORAGE OF FISH
Temperature of storage is the most important single factor affecting the storage life of frozen fish. Almost all cold stores for fish that have been built in recent years are designed to operate at -30°C, at which temperature the products will keep in first class condition for several months. Lean fish, such as cod and haddock, when stored for long periods at too high a temperature or in fluctuating temperatures can have marked changes in texture and flavour when thawed out. The thawed flesh may feel rubbery and appear dense white instead of translucent. After cooking they are found to be tough and fibrous or stringy.
Other causes of change in cold stored fish are dehydration and oxidation. Dehydration is kept to a minimum either by glazing unwrapped frozen fish before storing them, that is covering the surface with a skin of ice by dipping them quickly in cold water, or by packaging the fish in a material that is a good barrier against the passage of water vapour, for example polyethylene film. Fatty fish like herring are particularly prone to absorb oxygen from the air and so become rancid; these are therefore wrapped in a material that forms a good oxygen barrier. In addition the space between the package and the contents may be evacuated to reduce even further the risk of rancidity. The ideal packaging material for fish products is often a laminated film combining the desired properties of two or more plastics.
The cold storage chain is maintained in distribution by the use of insulated, refrigerated vehicles or containers, both of which operate at about -20°C, and frozen food cabinets, again at -20°C, in shops and catering premises.
The following Advisory Notes expand the information given on freezing and cold storage offish: 2 Handling sea frozen fish, by A. Banks; 8 Road transport of frozen fish, by D. L. Nicol; 12 Fish display in retail shops; 20 94 Temperature measurement in the fish industry; 27 Quick freezing of fish; 28 Cold storage of frozen fish: 34 Freezing at sea: advice to the crew; 35 Installing an air blast freezer? by J. Graham; 36 Rigor in fish: the effect on quality, by G. D. Stroud.
THAWING FROZEN FISH
The growth of quick freezing in the fish industry, and particularly the production of large blocks of whole fish for subsequent processing, has made necessary the development of thawing plant. There are two main types of equipment, those in which the fish are heated in a warm air stream or in warm water, and those which directly use heat generated by electricity. The method most used for large blocks of sea frozen fish is air blast thawing; the fish are conveyed through a stream of moist moving air at about 20°C until they are thawed enough to permit filleting or other processing. The fish temperature should never exceed 20°C. More detailed information on thawing is given in Advisory Note 25.
Bacteria and moulds generally cannot grow in the absence of water and hence drying can be used as a means of preservation. Salt, if present in sufficient strength, will slow down or prevent bacterial spoilage of fish. Drying or salting, or a combination of both, have been used in the fish industry for centuries but nowadays only a very small proportion of the catch in Britain is processed by these methods.
A few companies still make dried salted fish from cod and related species, by heading and splitting the fish, removing most of the backbone, and stacking the fish in piles with layers of salt between them. The juices withdrawn from the fish by the salt are allowed to run away and, after frequent restocking over a period of months, the water content is further reduced by drying the fish in a heated chamber until the moisture content is somewhere between 10 and 30 per cent.
Some herring are pickle cured, particularly in north-east Scotland and the Shetlands, although this export trade is a mere shadow of what it was earlier this century. The whole herring, having been lightly sprinkled with salt while awaiting processing, are first gibbed by hand or machine, that is the gills, long gut and stomach are removed. They are then packed in barrels with a layer of salt on each layer of herring until the barrels are full. After a day or two, when the herring have shrunk appreciably, the barrels are topped up with further layers of herring and salt, the lids are fitted and the barrels then laid on their sides for 8-10 days. After this period the barrels are up-ended, the lids removed, and the blood pickle from the upper half drained off through the bung-hole. To make ready for storage the barrels are finally topped up with fish, the lids replaced and blood pickle poured through the bung-holes until all spaces are filled.
Klondyking is the name given to another method of preserving ungutted herring using salt. The name is thought to originate from a method developed about the same time as the famous Gold Rush of 1897.
The herring, contained in baskets, are sprinkled with coarse salt, approximately 175 kg of fish treated with about 10 kg of salt, as they are tipped into a wooden box. Ice is then put on this mixture offish and salt, about 100-125 kg of ice to every 175 kg of mixture. Herring treated in this way could be kept in edible condition for approximately 1 week.
The canned fish industry in Britain is a small one, and the range of products is confined mainly to herring, sprats and pilchards packed in either tomato sauce or vegetable oil.
The process for herring in tomato sauce is typical. First the fish are nobbed by machine, that is the head and gut are removed. They are then immersed in saturated brine for up to 30 minutes and packed by hand into oval cans holding 200 g of fish. The tomato sauce is added, the can lids are lightly clipped on and the cans exhausted in steam for 10-15 minutes. The object of exhausting is to produce a partial vacuum in the headspace of the can which is not filled either with solids or liquids. The cans are then sealed, washed, and heat processed in steam at 115ºC for 55 minutes. After cooling, the cans are stored for about a month, labelled and packed in outer cartons for dispatch. The heat processing stage is critical, and is designed to inactivate all bacteria and enzymes present and in particular to destroy any harmful organisms.
There are a number of imported canned fish products that could be manufactured in this country from British-caught fish, and the canning industry is examining the possibilities of expanding their range.
The following Advisory Notes expand the information given on canned fish: 41 Canned fish, by R. McLay; 43 Delicatessen fish products, by R. McLay; 44 Handling fish before canning, by R. McLay.
The shellfish industry, although only a small part of the fish industry as a whole, has grown considerably in recent years, and the products are generally high value ones. The principal species in order of importance are Norway lobster or scampi, lobster, scallop, crab, cockle, crawfish and oyster. Mussels and shrimp make only small contributions to British landings at the present time, but their fisheries are capable of considerable expansion.
The Norway lobster is landed either whole or headless in ice, and is often frozen in the shell while awaiting processing. The meats are extracted from the thawed tails either by hand peeling or by blowing out with air or water jets. The peeled meats are frozen individually, either in an air blast freezer or a liquid nitrogen freezer, glazed and bagged and put into cold storage.
Lobsters are still distributed live inland; the few that are processed are normally cooked and then frozen whole. Crabs, which do not travel well, are processed close to the points of landing. They are boiled whole, and the meats are then extracted from body and claws by hand. The white and brown meats are frozen separately and then wrapped and cold stored. A small amount of crab meat is also canned in Britain, and small amounts of cooked whole crabs are distributed chilled to retailers.
The oyster is marketed live in shell, and the crawfish catch is mainly exported live to the Continent. The scallop, and its near relative the queen, are frozen in shell on arrival at the port processing plant, thawed as required and the meats removed by hand with a knife. The meats are frozen individually, usually in an air blast freezer, and bagged for cold storage; they are mainly exported to the United States. Cockles and mussels are boiled in the shell at the ports; the extracted meats may be distributed either chilled, frozen, or packed in jars in brine or vinegar.
Shrimps are cooked and peeled soon after catching, and the meats distributed either chilled, frozen or potted in butter; alternatively the whole raw shrimp are iced and then frozen for subsequent processing.
The following Advisory Notes expand the information given on handling shellfish: 6 Processing lobsters, by J. J. Waterman; 13 Processing mussels, cockles and whelks, by J. J. Waterman; 26 Catching, handling and processing crabs, by J. C. Early; 29 Processing Norway lobsters, by J. C. Early; 46 Catching and processing scallops and queens, by R. Hardy and J.G.M. Smith.
When the edible flesh is removed by filleting from whole fish landed for human consumption, the remaining heads, skeletons and other processing waste are disposed of by making fish meal. In addition whole fish, both white and fatty, that are surplus to market requirements or landed specifically for the byproducts industry are also converted into fish meal and oil. White fish and white fish offal has most of the water removed by cooking and drying, and the dried material ground and bagged for use as a high protein animal food, particularly in the pig and poultry industries. The yield is roughly one tonne of meal from 5 tonnes of raw material. Fatty raw material is pressed after the cooking stage and the press liquor, a mixture of oil, water and some solids, is further processed to separate the oils and solids. The oil-free solids are dried and ground along with the bulk of the solid material from the press. The refined fish oils make a valuable contribution to the manufacture of edible products like margarine.
Fish meal made from suitable raw material under hygienic conditions can be eaten by humans, and its possible use as a fish concentrate protein added to the diet of protein-deficient peoples in the developing countries is being investigated in many parts of the world. More details are given in Advisory Note 39, Fish protein concentrate, and Advisory Note 49, Fish meal, by M. L. Windsor.
Waste from the British shellfish industry is occasionally accepted in small quantities by the fish meal manufacturers, but most of the shells are at present unsuitable for the manufacture of byproducts.
Only a small part of this country’s requirements for fish
meal are met by the British industry; the possibility of reducing imports by
increasing the British catch of species unwanted for human consumption and
converting it into fish meal is at present being explored.
