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Fish is an extremely perishable food item. Owing to the high perishability of fish and fishery products, 90 percent of trade in fish and fishery products in quantity terms (live weight equivalent) consists of processed products. Fish are increasingly traded as frozen food (39 percent of the total quantity in 2010, compared with 25 percent in 1980). In the last four decades, prepared and preserved fish have nearly doubled their share in total quantity, going from 9 percent in 1980 to 16 percent in 2010. However, trade in live, fresh and chilled fish represented 10 percent of world fish trade in 2010, up from 7 percent in 1980, reflecting improved logistics and increased demand for unprocessed fish[i].
In high ambient temperature of the tropics like Nigeria, fish will spoil within 12-20 hours depending on species, methods of captures etc.[ii]. In the healthy live fish, all the complex biochemical reactions are balanced and the fish flesh is sterile. After death however, irreversible change that results in fish spoilage begins to occur. The resultant effect is the decomposition of the fish[iii]. The processing and preservation of fresh fish were of utmost importance since fish is highly susceptible to deterioration immediately after harvest and to prevent economic loss[iv]. This spoilage can be reduced or temporarily halted by various techniques.
Some of the aspects of fish processing include[v]
1. Fish Canning- Canning is a modern technological advancement in food processing which improves the shelf life of the fish enabling its storage for several years. The canning process involves hermetically sealing the product in a container, heat sterilizing the sealed product and cooling to room temperature for storage. An example is the popular sardine.
2. Mince Fish- Mince fish are fish flesh separated from the skin and bones. Separating methods may be mechanical using deboning machines or combined chemical and physical methods. The separated flesh could be processed into delicate fish products such as fish fingers, fishcakes, fish sausages which is sold frozen or part filled in oil.
3. Fish Silage-Fish silage or liquefied fish protein is a mixture of fish liquid by enzymes in the presence of an acid. This simple technology of processing fish or fish waste into silage is scarcely utilized in developing countries, because acids have to be imported. The raw material for silage production can be provided locally from the following:
· Catches from another fishery
· artisan seasonal glut
· Products of fish processes.
This serves as an excellent livestock feed.
4. Fish Meal-The production of fishmeal and oil is the predominant method of processing the world’s supply of non-edible fish and fish frames from filleting operations with the oil used in the leather, soap and pharmaceutical industries, and the residue as a source of quality fertilizer and livestock feed. This is achieved using the wet process or dry process.
5. Other processing and storage mechanism include drying, smoking, salting, roasting, frying, cooking, chilling and freezing among others.
STEPS INVOVE IN FISH PROCESSING
Fish processing is a value addition process which involve several precautions to ensure Food safety. Several requiements have been put in place to ensure processing facilities meet up with internationaly accepted practises of food safety. click here to read more
PRE PROCESS OPERATIONS
There are many types of fish products available to the consumer but most of them will have undergone some sort of initial preparation before processing. This preparation can be in the form of stunning of fish, grading, removal of slime and cutting the fish in a particular way to produce the raw material necessary for future processing. Due to the delicate nature of the fish and the rapid rate of deterioration that can occur if the fish is treated badly, it is extremely important to handle it hygienically and carefully during all stages of preparation.
Stunning of fish
Stunning of freshly caught fish or fish delivered live to a processing plant is best done with an electric current. First, the fish are placed in a tank of water and an electric current is then passed through the water to stun or kill the fish. Live fish are also slaughtered by cutting the aorta and bleeding to death. In some plants, water in the fish tank is saturated with carbon dioxide or salt, which renders the animals unconscious or dead.
Grading of fish
Sorting by species or on the basis of freshness and physical damage are still manual processes, but grading of fish by size is easily done with mechanical equipment. Size grading is very important for fish processing (i.e., smoking, freezing, heat treatment, salting etc.) as well as for marketing.
Removal of slime
Slime accumulating on the skin of dying fish is a protection mechanism against harmful conditions. In some fish species slimes constitutes 2-3% of body weight. Slime creates a perfect environment for microorganism growth and should be removed by thorough washing. Soaking fish in a 2% solution of baking soda and then washing in a cylindrical rotating washer can remove slime from freshwater species.
Splitting, gutting and filleting.
There are several reasons why we cut and gut fish.
1. To add value to the product (e.g. making fillets);
2. To make the product acceptable to the customer;
3. To maintain the quality by reducing spoilage;
4. To make further processing easier;
5 To reduce processing costs;
6. To improve storage life; and
7. To reduce transport costs/charges.
Splitting or opening the fish is usually done if the fish is to be salted, dried or smoked. It increase the cut surface area that is exposed to the air and decreases the thickness of he fish, so drying is faster,
Cutting and Gutting
Cutting and gutting is done to help reduce spoilage, as guts are full of bacteria and enzymes, and are not usually eaten. Making a ventral cut from the gill to the anus, pull out the guts with the fingers and thoroughly wash out the cavity.
These processes generally take place within separate areas of the fish processing plant. The fish are kept on ice in boxes before being delivered to the fish processing plant until required for further processing.
This can be processed into fillet or smoked.
[i] Culled from: FAO 2012 The State of World Fisheries and
[ii] Clucas, I.J. 1981. Fish handling preservation and processing in the tropics: Part I. Report of the Tropical Development and Research institute, G 144, VIII+ 141 PP.
[iii] Akinola, O.A., A.A. Akinyemi and B.O. Bolaji, 2006.Evaluation of traditional and solar drying systems towards enhancing fish storage and preservation in Nigeria (Abeokuta LocalGovernment as a case study). J. Fish. Int., 1(2-4): 44-49.
[iv] Okonta, A.A. and J.K. Ekelemu, 2005. A prelimnary study of micro-organisms associated with fish spoilage in Asaba, Southern Nigeria. Proceedings of the 20th Annual Conference ofThe Fisheries Society of Nigeria (FISON), Port Harcourt, 14th-18th November, pp: 557-560.