According to data published by FAO, 15% of the world supply of animal proteins is derived from fish. The demand for fish as food is systematically increasing but at the same time marine resources are close to the limits of exploitation. However, aquaculture which supplies the market with both marine and freshwater fish, is fast developing. Figure 1.1 shows the most important freshwater species in Europe.

Much of the freshwater fish found on Western European markets comes from aquaculture and only very limited quantities of fish are derived from the freshwater fishery; this is due to the poor economics associated with this sector. But it should be stressed that in the Central European countries e.g., in Poland, approximately only 50% of freshwater fish come from aquaculture.

The European market is dominated by the following fish species (Table 1.1):

- rainbow trout (Oncorhynchus mykiss),

- European eel (Anguilla anguilla),

- carp (Cyprinus carpio).

Table 1.1 Freshwater fish production in Europe (excluding former USSR) in 1990, and a forecast for the year 2000 (Hough, 1993)

Although trout production has doubled in countries of the European Union, to reach 190 000 t in the period 1980-90, the anticipated increase in production by 50 000 t by the year 2000 may testify to a restrained demand market. On the other hand, the increase in eel production is expected to exceed 200%.

Carp is greatly appreciated in Central European countries but only in limited regions of Western Europe.

Italy is the major European producer of eel, but Germany and the Netherlands are the biggest markets. Prices of eel depend on the size of fish (best prices are obtained for fish weighing more than 350 g). As much as 65% of the entire eel production comes from aquaculture, and fish derived from this source is considered more suitable for smoking than the wild fish due to its thinner skin and higher fat content.

Figure 1.1 The most important species of freshwater fish:

1. Rainbow trout (Oncorhynchus mykiss)

2. European eel (Anguilla anguilla)

3. Pike-perch (Stizostedion lucioperca)

4. European perch (Perca fluviatilis)

5. Northern pike (Esox lucius)

6. Wels catfish (Silurus glanis)

7. Mirror carp (Cyprinus carpio var. specularis)

8. Scale carp (Cyprinus carpio var. communis)

9. Freshwater bream (Abramis brama)

10. Roach (Rutilus rutilus)

Until recently, freshwater fish processing was carried out mainly in kitchens at home, in restaurants and in catering centres. Occasionally, fishmonger shops and small fish processing plants produced semi-products in rudimentary conditions and placed them on the market. However, changing requirements and habits of customers in Europe created the need for an increased market supply of ready-to-cook (e.g., fillets, chunks) or ready-to-serve dishes. This trend will intensify and, if they are not to lose the market, the existing processing plants will have to be modernized. The modernization should improve economies, simplify work and, most important, improve sanitary conditions of production. The introduction of modern machines results in the growth of productivity and reduction of employment; it shortens the duration of technological processes, and makes it easier to prepare more laborious but, at the same time, more attractive products for the consumer.

However, mechanization of the processing lines is very costly, especially for small plants processing freshwater fish. In these cases, mechanization of freshwater fish processing would be limited to that equipment needed to maintain the market and meet the basic sanitary requirements imposed by the competent authorities. In addition to infrastructure and the necessary machines - for example, ice generators, washers, smoking equipment, freezers, cold stores - small processing plants could, within reason, also acquire simple, inexpensive machines which often only perform one operation.

During the Eighteenth Session of the Advisory Board of the FAO European Inland Fisheries Commission, held in Rome in 1994, it was noted with satisfaction that needs for high quality freshwater fish products are growing, especially in the more affluent countries. The Commission made important recommendations for inland fisheries, among which:

- elaboration and distribution of publications on existing technologies of fish processing and marketing, with special regard to species of the Cyprinidae family

- arrangement of aid concerning the elaboration of new technologies for producing high quality fish products.

The problems related to freshwater fish processing are not sufficiently reflected in the scientific literature. Here, an effort was made to collect the information, often based on the authors' experience or technological processes used, and on the possibilities and trends in the mechanization of freshwater fish processing, with special regard to the Cyprinidae family.