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The types of losses in fish post-harvest and the reasons for them have e been described . The need for assessment of losses as a first step towards overcoming losses ways of identifying losses and defining solutions to the various problems have been explained. The final stage is to describe various of means of deducing losses These are described in detail in two NRI reports (Clucas et a1. 1981. 1982).
Much can he achieved by simple improvements in handling and processing methods The basic requirements is to take more care Fish is easily damaged and easily spoiled. Careless procedures will accelerate spoilage and increase losses careful methods will retard spoilage, reduce losses, and improve the quality of the marketed produced.
Chilling with ice is an extremely effective means of reducing spoilage in fresh fish. Ice is an ideal cooling medium; it is harmless, it has a very large cooling capacity for a given weight or volume, it is comparatively cheap, and it is able to cool the fish quickly by intimate contact with the fish. Although chilling can never prevent spoilage, the lower the temperature at which the fish is held, the greater the reduction of bacterial and enzymatic activity.
To chill fish, it must be surrounded by a medium which is colder than the fish itself. For effective chilling the ice must be allowed to melt; there are additional advantages in this as melting ice keeps the fish both moist and glossy, adding to its attractiveness to the consumer. The ice melt water also helps to wash away surface bacteria and clean the fish. Ice acts as a self-thermostat, and as about 80% of the total weight of fish is water, the fish is maintained at a temperature slightly above that at which it would begin to freeze. Another advantage of using ice to chill fish is that it can be transported fairly easily, as a portable cooling method.
If possible, fish should be iced on board ship, immediately after catch. Spoilage is so rapid, especially at tropical temperatures, that even a few hours' delay can mean that fish is starting to spoil before landing.
Chilling in ice at sea, soon after catching, will minimize spoilage and ensure that fish is attractive and in good condition on landing.
Many fishing vessels have a hold or fish room in which the catch can be kept in ice. Small-scale fishermen increasingly use insulated boxes to carry ice to sea, and to store ice and fish. These boxes are frequently made with walls containing expanded polystyrene of about 10-1 5 cm thickness, and they provide excellent insulation. Often they need to be made specially so that they fit into the hull of the fishing vessel. Placing them too high up might well endanger the stability of the vessel.
In one recent NRI project, on the east coast of India, ice boxes were specially made to fit the nave, the traditional type of fishing vessel. Using these boxes enabled the fishermen to land much better quality fish, increasing their income by 20% The widespread use of ice in other traditional vessels shows that many fishermen had themselves made similar observations.
Ice on shore
If fish is iced at sea, then it is important to maintain its quality by keeping it in ice during distribution and marketing. If it is not iced at sea, it is even more important to prevent further spoilage by icing it as quickly as possible. Insulated boxes like those described above may be used for transporting the fish to market. Often fish is loaded in ice in bulk, in open lorries.
Large insulated ice boxes may be useful at landing sites where fish has to be kept for a time before being taken to market. One such box is shown in Plate 32.
Types of ice
This is important. (rushed or flake ice is best, as it gives the greatest possible area of contact with the fish, ensuring that the fish is cooled quickly. With larger pieces of ice the fish will cool more slowly. With very large pieces, such as block ice, only part of the fish will be in contact with the ice, and only that part will cool quickly. In the rest of the fish, the spoilage processes will continue for some time.
Block ice is used in many developing country, fisheries. Smashing blocks of ice with a club or hammer (Plate 25) gives es smaller pieces but these have sharp edges which can cut into the fish. These cuts enable bacteria to penetrate the flesh more easily and spoilage is accelerated.
Alternatives to ice
For larger vessels, there are two alternatives to using ice on board. Chilled sea water and refrigerated sea water. These are systems in which the fish is kept in brine, which is cooled to about 0°. This is a bulk storage system, and it is convenient for holding fish caught in large quantities at one time. The fish is landed in the wet unfrozen form.
Another alternative is freezing at sea. This is very much the industrial level of fishing, and it is usual used in tropical countries only for shrimp.
Although ice is often a cheap product, it can be expensive in developing countries. Although it is extremely effective in showing down spoilage of fresh fish, its price can prohibit its use. Also many fishing villages have no electricity supply, and ice mv not be available. The fishermen have little choice hut to land fish as quickly as possible. Even so, there are some steps which can slow fish spoilage. It is useful to cover fish with sacking or other cloth, to stop direct heating hv the sun. Pouring water onto the sacking will cause some evaporative cooling.
Spoilage and loss of quality of fish can often he reduced by simple improvements in drying practices. Drying can he done on the earth, hut then the fish is bound to get contaminated with dirt. Drying on mats on the ground, or a hard surface such as concrete is better. It is better still to put the fish on some sort of racks above the ground so it is more exposed to any breeze. If the rack is not too solid, say wire mesh or an old fishing net, then troth sides of the fish can dry. Also, if the fish is away from the ground it is less vulnerable to domestic animals.
Smoking can be effected in any equipment which suspends the fish above a fire or in the smoke from a fire. However, in traditional smoking the fish often gets badly charred. Various types of improved kiln exist, in which the fish is placed in racks either over the fire or in a separate smoke chamber These make it possible to control the process and cook and dry the fish, without burning it.
Salting before drying or smoking can expedite processing, as salting removes much of the water from the fish. However it gives a very different product. In much of inland Africa, salt is expensive and consumers are not accustomed to salted fish, and do not readily accept it.
Use of salt Salt is known in many parts of the world as an effective deterrent to blowfly infestation. Investigations have also shown that salted dried fish tends to be less susceptible to beetle infestation than non-salted fish. Although it is generally understood that high levels of salt will be effective in reducing infestation, it is difficult to determine the minimum effective concentration required. Moreover it is difficult to assess whether this is a practicable method in the long term. Most of the trials have been carried out in areas where salt is not normally used, and there is usually some unsalted fish nearby. It could be that blowflies merely prefer the latter, given a choice. In areas where most or all fish is salted, like Indonesia, blowflies attack salted fish very readily. Also in areas where salting is not normally used, consumers are unfamiliar with the salty produce, and may not accept it.
Prevention of blowfly attack without insecticides The use of insecticides is discussed below; these are important because other methods may be ineffective. Screens can be placed over fish which is being dried, and they do prevent blowflies getting to the fish. Unfortunately they also slow down the drying process, and the fish spoils. Also blowflies have been observed to deposit their eggs on the screens, from which they drop onto the fish. Plastic greenhouses have been used but it proved virtually impossible to place the fish inside them without blowflies getting in as well.
Beetle infestation can be controlled by reprocessing. One effective method is to 're-smoke' stored smoked fish which has become reinfested over a hot fire. Another method, used in Malawi and elsewhere is to immerse infested dried fish in boiling water for a few seconds, then to redry it.
Use of insecticides The use of contact insecticides is extremely effective against insect infestation, but it is only justified under approved and controlled conditions. Insecticides are- highly toxic; and many are dangerous. Only a few are safe to use on foods. One of the safe substances is pirimiphos methyl, and this has been approved internationally for use on fish. It is extremely effective in controlling blowfly losses during fish drying. When used under specified conditions, it leaves no harmful residues. Pirimiphos methyl is also effective in controlling beetle infestation during storage.
Use of fumigants
Cured fish can be protected from beetle infestation during storage by the use of fumigants. These are insecticides existing in the gaseous form at ambient temperatures. As gases, they can diffuse into the dried fish and kill any insect infestation. It is important to remember that they do not provide lasting protection, and the product can become reinfested unless suitable precautions are taken. Two of the most effective fumigants for cured fish have been found to be phosphine and methyl bromide. It is crucial to remember that as fumigants are toxic gases they are very dangerous, so fumigation should only be carried out by trained personnel
Packaging
Careful packaging with suitable plastic materials can prevent insect infestation of cured fish. However such materials will only act as a physical barrier to insects, and they will not be effective- against any insects already present in the fish when it is packaged. The packaging material should be such that insects are unable to penetrate it by biting. The package should be well sealed, with holes that do not exceed 0.25 mm in diameter; perfect sealing is possible with some sophisticated materials, but these may have the disadvantage of being expensive. Such materials may also be waterproof, encouraging mould growth. Boxes sealed with adhesive tape or lined with cloth or paper will give useful protection against insect attack, as will closely woven heavy cotton sacking, although the stitch holes in the sack are potential entry points for insects.
Reducing mould attack Mould growth is encouraged by damp, so cured fish which has not been fully dried is susceptible, particularly after a period of storage. Mouldy fish can be cleaned with water and redried or resmoked. Care should be exercised in the case of very mouldy fish because of the possible presence of mycotoxins (very poisonous substances produced by some moulds). Heavily salted fish is likely to absorb atmospheric moisture, so careful inspection should take place regularly, particularly during rainy seasons. The fish should be redried if it appears to be becoming moist. As a long-term measure, fish stores should be used which are designed so that they provide protection from rain and ground water and are well ventilated.
Good packaging of properly dried fish can prevent mould attack during transportation, as the fish will be kept dry. However if plastic sheeting is used its waterproofing properties will encourage mould growth if the fish has not been fully dried before packing. One solution is to use a woven plastic fabric which is water permeable, and, unlike bessian, does not become damp itself. Alternatively the fish can be packed in a water permeable cardboard box, then protected by plastic sheeting.
Preventing fragmentation Serious losses occur in cured fish from fragmentation during handling and transport, since by its very nature the fish is brittle and friable. The fish should be packed in rigid containers such as boxes or baskets with frames, which provide some protection, and not in sacks or cartons which are too flexible. If baskets or similar containers are used their frames will ensure rigid protection, but if the weave is such that the fish is likely to fall through, then a lining of cloth or paper will prevent this. Cardboard or wooden boxes will protect the fish, and have the advantage of being made from a single material. Rigid containers must be strong enough to be stacked without collapsing, or compressing the fish, and they must be able to withstand jolting encountered in vehicles, and on rough roads. Individual packages should be able to be handled easily; a maximum size holding 1 15 kg. fish is recommended.
Fragmentation is much more likely to occur if the fish were in poor condition before curing. The spoilage processes in wet fish gradually break down the muscle structure. Poor quality fish, even if it is dried or smoked carefully will be friable, and pieces of the flesh will fall out much more easily than if the fish were fresh originally.
Preventing charring of fish can easily occur during processing. It is particularly common when very oily species such as mackerel are smoked and dried too close to the fire; the fat drips onto the fire and ignites, burning the fish.
This can be prevented by ensuring that the racks on which the fish rests above the fire are at a suitable distance from the fire, and that the fish is turned regularly during processing. Charring is also caused by the smoke from the fire or kiln being too hot, and control of combustion of the fuel should be attempted. In the simplest processes, when the fish is cured or dried over a wood fire, the wood used should be slightly damp, as then it will burn less violently and generate more smoke. If the fish is being smoked or dried in a kiln, then a well-designed kiln with flues to adjust ventilation will ensure greater control over the process.
For many types of processing, the fish must be split, gutted or cut; this often takes place on the ground or a beach, under unhygienic conditions. Often the fish waste is allowed to collect in heaps, or it is washed into the sea or lake, causing pollution. Such conditions are ideal for bacterial growth and contamination, accelerating spoilage.
Considerable improvements can be made by the use of simple hand-washable surfaces for cutting the fish, and by regular washing down of the surfaces with clean water. The fish waste should be disposed of well away from processing areas. contamination can be reduced if the fish is processed as soon as possible after it has been prepared, provided that it is first washed in clean water to remove any remaining viscera and blood.
If salting vats are used they should be washed out with clean water before refilling. Drying racks and floors should be kept as clean as possible, as should all fish processing areas.
Many tropical countries now earn much valuable foreign currency by exporting frozen shrimp and prawn. These may be whole or headless, shell-on or peeled, raw or cooked. In all these cases they are very vulnerable to bacteriological contamination. The importing countries have very strict regulations concerning levels of bacteria, and consignments may be rejected if these levels are exceeded. Processing factories must take extreme care in maintaining hygiene. Prawn farmers, fishermen, and everyone else involved must also take great care in keeping everything as clean as they possibly can, using clean containers, clean surfaces, good wash water, and ice made from the cleanest available water.
Much of the shrimp trawler by-catch consists of fish which could be sold and used if it could be kept in good condition while being transported to market. The basic problem is its low value, especially in comparison with the shrimp itself. Small shrimp trawlers, operating on short voyages, usually ice the shrimp, but the by-catch is often left to deteriorate. On landing priority is given, inevitably, to the shrimp. By the time the by-catch is taken ashore it may be fit only for use as fish meal, as an animal feed. Large shrimp trawlers have freezer facilities but they keep these for shrimp, and the by-catch is usually dumped overboard.
The huge potential food resource which by-catch represents has long been the subject of concern, and many efforts have been made to use it. In the 1970s particularly, these efforts were concentrated on the development of manufactured products from the by-catch. The plan was that if by-catch could be converted into higher-value products, then it would become profitable for trawlers to retain and land it. Much research was carried out on the use of by-catch in making food products such as fish soups, fish biscuits, etc. Unfortunately, very little came of this research, as there was seldom any commercial uptake of the products in question. There were two main problems. One was technical: the difficulty of producing any manufactured foodstuff from a starting material whose composition varied very substantially from day to day. The other was commercial: the limited consumer acceptance of the products in question. All too often, consumers preferred their soups or biscuits enriched with other types of protein.
The increasing demand for fish in its natural form and shortage of supplies in many areas, are leading progressively to the greater use of by-catch. Where there is a bigger demand for fish, and consumers are prepared to pay more for good quality material, it will be advantageous for trawler operators to retain at least some of the by-catch and keep it in good condition. Individual fishermen or crews find it becomes worthwhile to sort the bigger fish, and the preferred species, and to ice or freeze them. In Gujarat, in north-west India, King (1990) found that much of the by-catch was being iced on board small trawlers, and subsequently sent to cities like Bombay or exported to the Gulf. This practice had increased considerably over only a few years, compared with a study by Bostock in 1987. On the east coast of India, large trawlers making voyages of up to 30 days separate out of the by-catch many of the larger fish and freeze them for sale later in the major cities. In other places the demand for cheap fish for use as a feed for farmed shrimp encourages small trawlers to land by-catch, even in poor condition.
It seems certain that as the demand for fish increases, it will become more profitable to land by-catch and trawler owners will take advantage of this. In some places there may be a 'chicken and egg' problem: trawler owners may not land selected by-catch as no channel exists for distributing and marketing it, but no channel can develop until supplies of by catch fish become available. One of NRl's current projects in the Bay of Bengal Progamme is attempting to resolve this problem, and there be scope for similar 'catalytic' work elsewhere.
Any effective action to reduce losses will depend upon persuading fishermen, fish processors, and others to adopt improved practices. This is seldom easy, as people are understandably reluctant to change long-established customs on which their livelihood depends. It will usually be necessary to demonstrate that improved methods do generate more income. The use of ice boxes on traditional fishing boats (Plate 31) is an example. If a few enterprising people will agree to help, a demonstration can be organized. Then if the new methods really do generate more income, or improve living standards or working conditions, other people will adopt them. The women shown in Plate 35 soon showed enthusiasm for the aluminium containers to take fish to market; with them, they could travel by bus, instead of having to walk many miles with leaky baskets.
Demonstrating the advantages of improved methods will usually need the help of the local fisheries extension service. Training the extension officers themselves is then important. Training aids such as posters and leaflets (Plate 38), which can be translated into local languages can be very important, in disseminating information to the extension officers and the people involved in fisheries production.
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