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close this bookFish Handling, Preservation and Processing in the Tropics: Part 2 (NRI)
View the document(introduction...)
View the documentSummaries
View the documentAcknowledgements
View the documentIntroduction
View the documentSalting of fish: salt
View the documentSalting of fish: methods
View the documentDrying of fish: basic principles
View the documentDrying of fish: methods
View the documentSmoking of fish
View the documentMarinades
View the documentFermented fish products: a review
View the documentBoiled fish products
View the documentFish canning: theory and practice
View the documentFreeze drying
View the documentIrradiation
View the documentMiscellaneous products: crustaceans
View the documentMiscellaneous aquatic products used as food
View the documentFood by-products
View the documentNon-food by-products
View the documentNew and delicatessen products
View the documentFish meal
View the documentFish silage
View the documentChemical and physical methods of quality assessment
View the documentOrganoleptic (sensory) measurement of spoilage
View the documentMicrobiology of spoilage
View the documentMicrobiology of fish spoilage
View the documentPublic health microbiology
View the documentInternational standards for fisheries products
View the documentLarge-scale fish landing facilities
View the documentSmall-scale landing facilities: design and operation
View the documentRetail sale facilities
View the documentFisheries extension services: their role in rural development
View the documentTraining in the field
View the documentAppendix

Retail sale facilities

Retail facilities may be provided in markets and this is common in South East Asia, where a number of stallholders rent facilities from a municipal or other authority and display their wares alongside one another. The advantages of this system are that wholesalers have to deliver only to one central point; housewives can easily compare prices and values offered by particular stallholders; retail markets for other goods can be nearby so that housewives can buy all their daily supplies at one point in the city; and waste disposal is a relatively simple matter. This does, however, have the disadvantage that housewives have to travel to the market.

In many other parts of the world, shops are provided near to where people live. In other cases, as in outlying country districts in England, mobile retail facilities are provided: a van carries fish into the villages and the fish are sold direct, from the back of the van. Pedal-driven facilities have also been used in some parts of the world.

Whatever arrangement is decided upon, facilities should be provided for the retail sale of wet, smoked, dried and frozen fish. The requirements for each are quite different. In many cases, it is also necessary to provide facilities for the sale of live fish.

Sales of wet fish

Fish spoil mainly because of the activities of bacteria and the speed at which these grow on fish flesh depends largely upon the temperature. Fish taken straight out of the sea and kept at 0°C by placing them in crushed ice can remain fit to eat for almost 3 weeks. If kept at 6°C, they can keep for only about 6 days and, at 11°C, they will be inedible after 3 or 4 days.

The first essential in looking after wet fish is, therefore, to keep them as close to the temperature of melting ice as possible. The best way to do this is, of course, to keep them buried in melting ice. Obviously, it is easiest for the fishmonger to keep his fish buried in melting ice by holding them in boxes with ice rather than attempting to display them on a bench. Some fish must, however, be displayed on the bench so that people can see what is for sale. Therefore, a sales bench must be provided; this is best made in the form of a slab which is sloped to provide drainage and for ease of cleaning. The slope should not be excessive or the fish and ice placed upon it will slide down. The slab should be covered with a bed of ice and the fish pushed into this; ice should be piled round them so that only the top surface of the fish is visible, which allows the fish type to be identified. Where possible, a glass cover should be provided so that fish are kept under a pool of cool moist air and are shielded from draughts. Figure 18 shows a suitable arrangement. The sales slab should be backed up by storage boxes or by a chill store.

Figure 18 - Fresh fish ideally displayed on ice

The use of chill stores alone for cooling fish is very bad practice: the appearance of the fish will rapidly be spoiled by the drying of the surface and, if the room thermostat is not sufficiently accurate, it is possible to freeze the fish, which will give very poor results when they are finally eaten. The best way to store wet fish is to put them in boxes with plenty of ice and then to put the boxes in a refrigerated store which is set at about 2°C. There would then be no risk of freezing the fish. There should be at least one and preferably two thermometers in different parts of the store to make sure that it is not too cold. The thermometers should not be hung on or near the cooling grids but near the actual fish.

There are a number of practices which should be avoided in constructing a sales slab. There is really little point in attempting to refrigerate it except where fish are to be sold in a sophisticated store. Even there, the fish must be surrounded by ice, the refrigeration being used only to prevent excessive wastage of ice. The fish must not be piled deeply on the slab. They should not be subjected to an air current from a fan, even the coldest moving air will dry them out. Whilst it is obviously desirable to have a light over the fish so that they can be seen clearly, the light should not be too powerful or too close to the fish or it will cause an increase in their temperature. All draughts which are likely to bring in dirt and bacteria should be avoided and, of course, the fish should not be displayed where the direct rays from the sun can warm them. A slab should be arranged so that it is sloping and can be easily cleaned. The drain should be as straight as possible and it must be large enough to take pieces of fish. Small narrow twisted drains can rapidly become blocked and useless. Figure 19 illustrates some points of bad practice.

Figure 19 - Bad practice in retail display

The floor in any retail facility should be made from material which is easily kept clean by scrubbing. Concrete provides a reasonable compromise between the ideal and that which is cheap enough in practice. The floors should slope to wide gullies which should in turn slope to a trap at which fat and fish waste are easily removed; the effluent should pass either to a sewer or to a septic tank.

The walls should also be easily cleansed. While tiling may be considered ideal, plastered concrete which can be scrubbed will have to suffice in most cases.

The comers between the walls and the floors should be curved for ease of cleaning. A high roofed building is obviously more easily kept at an equable temperature than one with a very low roof but will be more expensive to construct. Adequate ventilation must be provided and this should be screened to keep birds out.
It should not be necessary to screen to keep flies out and, provided waste is disposed of properly, there should be no fly problem. Where flies do exist in large numbers, screening is usually ineffective because every time the door is opened flies enter. Every stallholder should have a covered bin in which he places waste which is discarded at the end of the day.

Fish should be cut on boards, not on the slab surface. The best fish cutting boards, which are made of plastic, are extremely expensive and the best substitute for these is a board made of edge grained hardwood. Knives and choppers should be kept sharp and facilities for sharpening should be available.

All the facilities so far discussed for the sale of wet fish should also be provided in a mobile fish shop. Usually this must be provided with a tank to hold chlorinated washing water, which is kept at a high level so that it feeds by gravity to the points at which it is needed, and with a storage tank, at a low level, which can later be emptied into a sewerage system.

Both retail markets and fish shops should have some means of storing ice. In the larger markets, it is perfectly easy to manufacture ice and hold this for sale to stallholders. It is now possible to buy small ice-making machines which will manufacture 100 kg of ice a day which is adequate for many shops. Where possible, a flake ice machine should be used; some of the small machines manufacture ice in the form of pellets or small cubes which are not really suitable for use on fish.

Sales of frozen fish

Frozen fish may arrive at the point of sale in a number of different forms; sometimes it arrives as whole fish which have not been wrapped, sometimes as fillets which have been wrapped, packaged and frozen; in other cases, it arrives as cooked frozen fish which only needs re-heating before serving.

If frozen fish are to be sold as frozen fish, they must be kept in refrigerated storage. Prior to delivery to the retail facility the frozen material should have been held at - 30°C. In practice, however, the storage is likely to have been slightly warmer and, during carriage from the cold store to the retail shop, the fish may warm up further.

Figure 20 - Correct use of zero cabinet

Much of the frozen fish sold in Western countries is sold from what are calied 'zero' cabinets because they are held at 0°F (this equates to - 18°C.). If fish are held for a month at this temperature, they will suffer little harm; however, if they are held for several months at this temperature, they will be of somewhat poor eating quality. It is important, therefore, that the retailer should hold as little frozen fish as possible.

Figure 21 - Misuse of zero cabinet

Material which is kept in a zero cabinet should be treated like any other frozen fish in cold storage; it should be kept glazed and properly packaged to prevent dehydration. It is particularly important that the practice of 'first-in, first-out' should be followed so that material is held for as short a time as possible. This may mean that the retailer must personally date-mark the produce which he has for sale. If he does not wish the public to know how long he is holding material, he can devise a simple code.

There are a number of points to watch when handling frozen material. Good storage practice is illustrated in Figure 20; poor practice, in which a cabinet is misused, is illustrated in Figure 21.

Remember that material will deteriorate in the cabinet. The cabinet must be kept switched on so that it remains cold. it should not be loaded above the marked load line; if it is, the material above the load line will suffer an increase in temperature.

No attempt should be made to use the cabinet as a freezer since this will result in damage to the material already in storage because its temperature will increase before the new material is frozen.

Where one is available, a competent refrigeration engineer should be employed to service the cabinet at regular intervals. Some cabinets defrost automatically at short intervals. If the cabinet is not automatic, it should be defrosted regularly. It is a good idea to make a daily check of the temperature of the air in the cabinet; the best way to do this would be to place at least two accurate, adequately protected thermometers in different positions in the cabinet. Neither of these should be in contact with, or near, the cooling coils.

If the wrapping of any of the packages delivered is broken or torn, drying of the commodity will occur. Quite apart from the fact that there will be a loss of weight, the final product will be dried and unattractive (i.e. freezer burn). Such damaged materials should not be accepted at delivery and, if damage occurs within the shop, the material should be destroyed. The cabinet should be situated so that it is not in direct sunlight, lighting should be sited so that it cannot warm the cabinet and, most important of all, the cabinet's vent should be unobstructed so that the refrigeration machinery can operate efficiently without overheating.

In some developing countries, a system of retail marketing of frozen fish has been developed in which the fish are delivered frozen to a cold store and are then removed so that they thaw at point of sale. This material competes directly with wet fish. This system can work quite well but it is debatable whether it can be as effective as an ice storage chain. Where the system has developed, it seems to have done so because the market is readily supplied by large trawlers freezing the catch at sea as in West Africa. There is little doubt that better quality material can be provided by icing in most other circumstances; it seems likely that an icing chain would also be more profitable but, in designing a marketing chain for new points of sale, the alternative possibilities should be costed. As in other areas of fish handling and processing, much depends on the market demand.

Sales of smoked and dried fish

Fully cured, smoked and dried products are much easier to handle than wet or frozen fish since they do not require chilled or cold storage. They should, nonetheless, be carefully handled.

All cured products deteriorate quicker at high temperatures than at low temperatures so it is worthwhile taking some trouble to ensure that the products are not over-heated. At the same time, the products should be protected from excessive drying where they are sold by weight since considerable weight losses could occur if the products continue to dry.

The product should of course be kept clean. Generally this requires that items be either weighed into packets or individually packaged. The modern plastics have revolutionised packaging but should be used with care. Most dried products are really only semi-dried and, if these are packaged in a sealed container, they will sweat and spoil. Most products therefore require a ventilated packet.

Sales of live fish and crustacea

Both fin fish and crustaceans, such as rock lobsters and lobsters, can only be kept alive for reasonably long periods by keeping them in water. A few catfish and other species with accessory air breathing mechanisms are exceptions to this rule.

Molluscan shellfish, such as cockles, oysters and mussels, can be kept alive in cool moist air. All that is needed for these is a container made so that it drains readily, i.e., a wickerwork or wire mesh basket in which the shellfish can be refreshed occasionally by pouring water over them. The container must, of course, be stored in the shade, not in the open sun.

Almost any container of suitable size can be used to hold live fin fish and lobsters for sale, including glass sided tanks in which the animals can be seen swimming. Such expensive and elaborate facilities are, however, not really necessary. Concrete tanks, galvanised iron baths and plastic dustbins have all been used successfully. Metal containers should always be treated with some suspicion, particularly for sea fish, since very minute quantities of copper, zinc and heavy metals will kill fish.

Any of the catch which dies should be destroyed and not sold.

The water in which the fish are kept must itself be clean and uncontaminated; chlorinated public water supplies are quite unsuitable since relatively small quantities of chlorine in the water will quickly kill the fish. Where the public supply is not chlorinated {as it should be), it could be used to keep fish alive and, under these circumstances, no aeration would be needed; water could be permitted to flow through the storage tanks. Water usually has to be bought, however, and, even under these circumstances, it might well be cheaper to provide aeration to the tanks.


Aeration would best be provided by driving air stones from pumps operated from the electric main. The air stones should be sited at one end of a rectangular tank so that the water is caused to roll. This provides far more effective aeration than can be obtained just with the air stone bubbles. The aeration should be as vigorous as possible without causing physical damage to the fish. The fish must not be unduly crowded; a tank which holds 100 litres of water will not hold more than 25 - 30 kg of fish when fully loaded and, under these circumstances, even with very vigorous aeration, the fish are likely to die in a day or two. No hard and fast rules can be set. Oxygen deficiency is the cause of most deaths: different species have different oxygen demands and the warmer the water, the less oxygen it can hold and so on.

Certain obvious precautions should be taken: the fish should be permitted to scour before storage; they should not be fed in store; and the water should be kept as cool as possible, consonant with not killing the fish by cold shock.

It is perfectly possible to design a closed system, even for marine fish, at a distance from the nearest supply of clean, unchlorinated, running water. Such closed systems must include a good filter as well as good aeration. Simple biological filters can be constructed using sand and these, when run in, can be very effective.