Post-Harvest Losses of Fish in the Tropics (NRI) Economic losses (introduction...) Wet fish Cured fish

Post-Harvest Losses of Fish in the Tropics (NRI)

Economic losses

Physical losses in fish tend to be absolute, as the fish can either be eaten or sold, or it cannot. They could be measured, but losses in value, or economic losses, are gradual and progressive and very much more subjective; different groups of people may hold different views of the 'worth' or value of a particular product. The value of a batch of fish of a particular quality will vary from one day or week to the next, and in different places.

Wet fish

Much of the fish caught by small-scale fishermen in developing countries is sold immediately after capture, as fresh fish is usually more popular than cured fish, and it commands a higher price. Although ice is increasingly being use-d in more developed areas to preserve the fish, the greater part of the catch is sold without any further form of preservation. The various types of spoilage of fresh fish were described in the previous section, and it was emphasized that fresh fish is extremely perishable. Spoilage of fresh fish is usually accompanied by a loss in value of the catch, since most consumers will pay a higher price for fish which is in good condition. The relationship between the value of good quality fresh fish compared with poor quality fish is more complicated than it would first appear, as it varies considerably between different places and different countries.

Sometimes iced fish can command the highest price, and sometimes uniced. This depends on local custom. Always consumers want fresh fish. In some markets fish is sold uniced, soon after landing, but if it is not sold quickly it is iced, to be offered for sale next day. Then uniced fish is fresh, iced fish is yesterday's. These attitudes may change, if supplies Of fresh iced fish become available, and consumers come to recognize the better quality. What is beyond question, however, is that fish which is beginning to go putrid will not command as high a price as fish which is in a reasonable state of preservation. Therefore, if the fish can be landed and sold to the fish consumer within a few hours of catching, the loss of value can be negligible. Alternatively, if ice can be used on board, or at least after landing, the value of the fish will not drop for some days. If the- fish cannot be iced the drop in value will be rapid, and the economic loss to the fishermen or trader will increase. Fishermen or traders will do their utmost to sell fish in the wet state, reducing the price as the quality deteriorates in order to make a sale.

Economic loss can also occur if the handling distribution marketing chain is inefficient, or breaks down, resulting in delays in distribution of the fresh fish, and consequently spoilage ensues.

Some highly priced seafood particularly shrimp, is exported. (consignments may be rejected because the quality standards of the importing country, are not met, because of bacterial contamination, the presence of heavy metals, chemicals or other pollutants. This will result in economic loss for the exporter.

Another form of economic loss occurs with glut catches. Presence of a glution the markett will reduce the price, and therefore the value to, the fisherman or trader of the fish. If the fish is being sold the processing, traditional processing techniques art time consuming and drying facilities are usually tailored to cope with normal catches. If there is a glut catch, then many tonnes of fish may spoil because processing facilities are inadequate.

Assessments of economic losses in fresh fish have been made in various countries, but bv their very nature are open to a wide degree are of error as major assumptions have to be made about market prices and consumer requirements. Bostock (1987) in India estimated economic losses over potential 6 million per annum in the marketing of 60000 tonnes per anum of the fish for domestic infestation. A common source of loss is when processors are reluctant to buy fish from fishermen during wet weather, leaving the fishermen no choice but to discard their catch Conversely if the fish is dried at too high a temperature and too high a rate, the surface of the flesh can form a hard crust (case hardening) which reduces the rate at which water from the center can reach the surface and evaporate. Then autolytic and bacterial spoilage can occur within the fish whilst its exterior appears to be completely dried.

Salting Salting can he an effective way of reducing the water content and water activity of fish flesh, before drying or smoking, and of accelerating these preservation processes. Salting is used mostly in coastal areas, where salt itself is cheap and plentiful. In inland areas. salt is often expensive and rarely used. Because of the cost, and because consumers are unfamiliar with salt-cured fish, this means of preservation is not generally popular in inland African countries.

If added in sufficient quantities to fish, salt competes with bacteria for water, leaving the bacteria unable to grow and reproduce Insects are deterred alla utolytic enzymes are inactivated by salt Salting is only effective, however, if the salt is able to penetrate the tissues of the fish rapidly, otherwise the interior of the thicker fleshy parts remains vulnerable to spoilage.

Such inefficiencies in traditional processing will lead to economic loss Hanson and Esser (unpublished) in Indonesia found that losses of flesh of about 9% caused by insect damage during sun drying caused financial losses of about 30% It has also been found that, under the very humid conditions prevailing in some tropical countries, cured fish, particularly if it has been salted, will reabsorb moisture and become susceptible to mould attack, a relative humidity of over 70% being reported by Suryanarayano et al (1 1962) as being conducive to attack by moulds. Mouldy fish will fetch a lower price in the market, resulting in economic loss.

in many countries, the consumer preference for cured fish is for a fairly moist product This inevitably has a shorter storage life than the drier products Unless the moist product is scud quickly it will start to spoil. Then it is necessary to re-dry or re-smoke it to extend the storage life. This reprocessing involves more labour and, in the ease of smoking, more fuel. the cost of this reprocessing, even if it results in a sale, will represent an economic loss to the processor.

Cured fish

The purpose of curing fish by smoking, drying and salting in developing countries is to preserve it for longer than is possible in the fresh state . Product such as smoked salmon are not considered here. In these cases, the main project of smoking is to modify the flavour, and the product is still perisable, and it has to be kept refrigerated. It is fundamentally different from most types of cured fish produced in developing countries. Cured fish, however, is generally, not as popular for human consumption in developing countries as fresh fish and so its value is lower. Therefore an economic loss can be sustained by the processor who has, in addition to meet the costs of the curing processes.

Although traditional curing methods are well suited to the needs of the developing countries inefficiencies in such processes will result in a lower quality product, and there will be their economic losses to the processor, distributor or trader.

Inefficiencies in traditional processing

Smoking Fish is cooked over a hot smoke fire, and the process reduces the water content of the flesh, kills bacteria and insects and denatures enzymes which cause autolytic spoilage. If, however, the process is not carefully controlled, physical fragmentation of the fish will occur, and pieces will fall into the fire and be lost. Temperatures which are too high can lead to charring and burning of the flesh, resulting in nutritional and physical losses. If the smoking drying process has not reduced the water content of the flesh sufficiently, the fish will quickly become recontaminately with bacteria, often more pathogenic shall those present before processing.

Drying fish can be dried of the sun and wind, and, as mentioned above, by prolonged smoking. If however the weather is wet or humid, the highly water vapour content of the atmosphere will mean a very slow rate of evaporation from the surface of the fish and the fish will dry very slowly. If the moisture content is not reduced rapidly enough, the fish will remain susceptible to bacterial spoilage and blow fly of cured fish, and are able to obtain sufficient lysine from other foods. However, many people in developing countries rely on cured fish for most of their protein needs, and then the loss of available Iysine may he significant. It is often the lower income groups who depend most on cured fish, and they are less able to afford other protein foods which are richer in Iysine.