Electronic Journal of Polish Agricultural Universities (EJPAU) founded by all Polish Agriculture Universities presents original papers and review articles relevant to all aspects of agricultural sciences. It is target for persons working both in science and industry,regulatory agencies or teaching in agricultural sector. Covered by IFIS Publishing (Food Science and Technology Abstracts), ELSEVIER Science - Food Science and Technology Program, CAS USA (Chemical Abstracts), CABI Publishing UK and ALPSP (Association of Learned and Professional Society Publisher - full membership). Presented in the Master List of Thomson ISI.
Volume 8
Issue 2
Agricultural Engineering
Available Online: http://www.ejpau.media.pl/volume8/issue2/art-20.html


Andrzej Dowgiałło
Sea Fisheries Institute in Gdynia, Poland



The analysis of causes of limited carp industry processing is presented in the paper. The main obstacle is the presence of many intermuscular bones in the muscles of products. Cutting intermuscular bones into small pieces that are undetectable in the mouth is the only realistic solution for this problem. The paper describes new possibilities to mechanize this operation in relation to such carp products like carcasses or semi-fillets.

Key words: carp, processing, intermuscular bones.


According to data presented at the FAO conference that accompanied Fish International 2004 in Bremen, the farming of freshwater and marine fishes is the only way to increase their supply. Ecological theory suggests that the maximum sustainable yield for many aquatic wild populations has already been reached. It is estimated that the current equilibrium between demand and supply will last until 2005, while demand will exceed supply by 30 million tons in 2015 and by 92 million tons by 2030.

Freshwater fish will play a significant role in meeting demand. The most popular of these fish is carp, which is cultivated in many European and Asian countries. Carp comprises from 50 to 60% of the production of freshwater fish depending on region (tab. 1).

Table 1. Freshwater fish production in 2002 (thousands of tons)*







Freshwater fishes

20 930.7

18 945.0

14 047.9



Most farmed carp species**)

10 618.5

9 980.9

8 579.8



*Source: FAO Fisheries Department [5]
**common carp, silver carp, bighead carp and grass carp

Carp has several advantages that make it so popular for commercial culture:

Thus, carp farming is both more economical and easier to integrate with other conventional farm activities than are other types of aquaculture. However, despite these undisputable advantages and the previously mentioned disparity between supply and demand, it is difficult to speak of the dynamic development of global carp production. Only in China, where carp cultivation began at least 2500 years ago, is it growing considerably and at an extraordinary pace (fig. 1).

Figure 1. Production of the most farmed carp species (common carp, silver carp, bighead carp and grass carp) [5]

In Europe, the second largest carp cultivation center in the world, annual production has remained nearly stable at 400 thousand tons.

Figure 2. Production of most farmed carp species in Poland [5]

In Poland, the magnitude of carp production in the 1984-2002 period fluctuated strongly (fig. 2), and there has been a steady decline since 1995. According to FAO data, Poland´s current production of approximately 30 thousand tons places it fourth among carp producing nations following the Russian Federation, Ukraine, and Germany.


The main cause of stagnation in carp cultivation and processing is limited demand. In many countries, including Poland, carp are consumed primarily during the Christmas holiday season, while in other countries, such as the USA, carp are not viewed as fit for consumption. The main obstacle is the presence of many intermuscular bones in the muscles of products such as deheaded and gutted fish, semi-fillets (fillets with unremoved ribs), fillets, and steaks. Although intermuscular bones are referred to as pin bones in the literature [2], they should not be confused with the another ones, which are tiny bones that extend from the backbones and remain in the fillet after filleting (fig. 3). They can be removed easily by hand with a handheld mechanical device or with a special trimming machine.

Figure 3. Bony parts: 1 - centrum, 2 - neural spine, 3 - pleural ribs,
4 - pin bones [7]

Intermuscular bones are spike-like formations that occur when ligaments calcify. They lie on the intermuscular borders of both sides of the fish both over and under the backbone. Figure 4 presents bone distribution in carp. There is disagreement among ichthyologists regarding the connection of these bones with the backbone. According to Knorr [7], they are not connected to the backbone, while Patterson and Johnson [10] maintain that the single, unbranched ends of intermuscular bones are not free but attached to the vertebrae by ligaments from their simple (non-brushy) branches.

Figure 4. Distribution of bones in carp [9]

Regardless of whether they are connected to the backbone or not, carp intermuscular bones have varied shapes and sizes (fig. 5), and the number of them is an individual characteristic. According to Lieder [9], they number from 99 to 104.

Figure 5. Carp bone shape [4]

Due to their stiffness and branched shape, the intermuscular bones of cyprinids pose a health hazard to consumers and can even be fatal, especially in children. According to Vagholkara [11], fish bones are among the commonest foreign bodies found in the upper aerodigestive tract. Furthermore, consumers, especially those in industrialized countries, do not like to eat fish meat with small bones and prefer boneless fish fillets. This is why there has been an increase in the preference of such products on the global market. Therefore, consumers might accept a maximum of two bones per block as tolerable for the market [6].

Limited demand for carp is not only responsible for stagnation in the processing industry; it has also caused a slow-down in the development of mechanization. There is a lack of carp processing machines in Poland and Europe [8, 12]. The availability of equipment for producing fillets, semi-fillets, steaks or deheaded and gutted fish is quite limited. Despite technical progress, the main carp processing equipment is comprised of a simple knife and a working table [8, 12]. The necessity of performing difficult manual processing means that most carp are sold on the market alive or as whole carcasses. This, along with the challenges of preparing the fish in the home, also contributes to limited demand.

It should be added that the problem of bones does not occur in canned, minced or deboned meat products (fishburgers, fishsticks, etc.). The high temperature applied during can sterilization causes the bones to soften making them harmless to the consumer. In minced meat, the bones are crushed into such small pieces that they are no longer detectible.


Effecting a change in the attitude of the consumer towards carp can be done most easily by eliminating the previously mentioned problems and threats from the products that are traditionally found on the Polish market - carcasses, steaks, and semi-fillets. Substantial increases in carp demand should be possible by ensuring higher quality in the traditional products the Polish consumer is accustomed to and by promoting this with an information campaign. New products can be distributed to sales points within retail networks and sold as semi-products for final preparation in the home. They should also be served ready-to-eat at bars, restaurants, and other food service outlets. The production of such products requires an additional processing operation that would eliminate the threat posed by bones; this would allow producing products of a new and more healthful quality.

Removing bones from carcasses or steaks is physically impossible for obvious reasons. It is also impossible to remove them from fillets or semi-fillets, as is also the case with salmon. Research indicates that the anchoring of the branched intermuscular bones is stronger than their tensile strength, which equals 2.90 ±1.33 N [4]. This refers not only to carp but also to other cyprinid fishes. Due to this, cutting intermuscular bones into small pieces that are undetectable in the mouth is the only realistic solution for this problem. Although known for years, this solution has been practiced only in domestic kitchens and has not been put into practice on an industrial scale due to a lack of the appropriate machinery (fig. 6).

Figure 6. Carp with bones that have been cut manually [1]

Only the cutting of bones in fillets of carp and other cyprinid fishes has been mechanized. Intermuscular bones can be cut into lengths not longer than 3-3.5 millimeters with a row of revolving disc knives in the handheld mechanical device (fig. 7).

Figure 7. Rudolf Klein Firm handheld device for cutting intermuscular bones in carp fillets

This device cannot be used to cut the bones of the semi-fillets available on the Polish market since the ribs are intact. Manual cutting is also not practical on an industrial scale because it is too labor intensive. If the bones are to be cut like in the hand-held mechanical device, a one-kilogram carp would require approximately 120 cuts on each side. This is why the fundamental condition for the intensification of carp production is developing and constructing a machine to cut the bones of deheaded, gutted, and semi-filleted carp. Machines to do this have to meet the following requirements:

Additionally, given the technical capabilities of small processing facilities, the simplest construction solutions possible should be applied in the design of these machines. This would not only simplify machine exploitation, it would keep down the costs of outfitting such facilities.

It should be added that designing properly functioning machinery is a realistic task. This is indicated by the results of initial investigations conducted at the Sea Fisheries Institute in Gdynia on a mechanized model for cutting bones in carp carcasses. The model used in studies of this machine is presented in figure 8.

Figure 8. Model of a machine to cut bones in cyprinid fish carcasses

Growth in the Polish carp industry is not only limited to constructing and implementing a machine for cutting bones in carcasses and semi-fillets. Deheading and gutting, both of which have been performed manually to date, must be mechanized. The results of investigations conducted at the Sea Fisheries Institute in Gdynia [3] should be used to construct and implement in processing a machine for deheading and gutting. These machines, together with the semi-filleting machines constructed by MIR and the bone cutting machines for carcasses and semi-fillets currently in development, will allow for a mechanized production line in carp processing. This will enable the production of less labor-intensive, and thus cheaper, value-added products. Thanks to the neutralization of the bones, these products should meet with greater consumer approval. In turn, increasing demand will certainly stimulate not only greater interest from carp processing facilities but will also fuel the development of processing mechanization.


  1. Antalfi A., Tőlg T., 1975. Ryby roślinożerne [Herbivorous Fishes]. PWRiL Warszawa [in Polish].

  2. Coad B. W., McAllister D. E., 2004. Dictionary of Ichthyology. http://www.briancoad.com/Dictionary/I.htm

  3. Dutkiewicz D., Dowgiałło A., 1995. Wykorzystanie właściwości morfometrycznych ryb słodkowodnych w projektowaniu odgławiarek [Applying morphometric characters of freshwater fish to design deheading machines]. Zesz. Probl. Postęp. Nauk Roln. 424, 45-52 [in Polish].

  4. Dutkiewicz D., Dowgiałło A., 2004. Maszyna do przecinania ości w tuszkach ryb karpiowatych [Machines for cutting intermuscular bones in cyprinid carcasses]. Inż. Roln. 5(60) [in Polish].

  5. FAO Fisheries Department, 2000. Fishery Information, Data and Statistic Unit. FISHSTAT Plus: Universal software for fishery statistical time series. Version 2.3.

  6. Horner W. F. A., Dillon M., 1977. QACP: The application of HACCP principles to the assurance of fish product quality as well as safety. [In:] Seafood from Producer to Consumer, Integrated Approach to Quality. J. B. Luten, T. Borresen, J. Oehlenschlager, editors. Elsevier Science B. V.

  7. Knorr G., 1977. Cyprinus Carpio. [In:] Atlas zur Anatomie und Morphologie der Nutzfische. Verlag Paul Parey. Berlin

  8. Knősche R., 1995. Equipment: Chairperson´s Summary. Aquaculture 129, 467.

  9. Lieder U., 1966. Untersuchungsergebnisse über die Gratenzahlen bei 17 Sußwasser-Fischarten. Zeitschrift für Fischerai, Band X N. F., Heft 4/5, 329-350.

  10. Patterson C., Johnson G. D., 1995. The intermuscular bones and ligaments of teleostean fishes. Washington, D.C.: Smithsonian Institution Press.

  11. Vagholkar K. R., 2000. Fish bone injuries of the upper aerodigestive tract. Bombay Hospital Journal 42(3), 508-509.

  12. Váradi L., 1995. Equipment for the production and processing of carp. Aquaculture 129, 442-456.

Andrzej Dowgiałło
Sea Fisheries Institute in Gdynia, Poland
1 Kołłštaja Street, 81-332 Gdynia, Poland
email: techmech@mir.gdynia.pl

Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.