1.3. ECONOMIC IMPORTANCE OF FISH

Fishes are one of the most important group of vertebrates serving as food for human. They possess a great economic, nutritional, medicinal, industrial, aesthetic and religious values as well as providing employment for millions of people in the world. They contribute to food security in many regions of the world, providing a valuable supplement for diversified and nutritious diets. Consumption of fish has several health, nutritional, environmental and social advantages over other terrestrial animal meat. The importance of fishes can be discussed under the following headings.

I. Food value
Fish serves as an important food for human. Edible tissues of fish are appreciably greater than that in chicken, pig and sheep/goat. For example, approximately 65% of the raw weight of finfish is eaten, compared with 50% of chicken and pigs, and 40% of sheep/goat; fish are supported by water, but terrestrial animals and birds require comparatively strong bones so they spend their substantial energy into the growth of the bones, which cannot be consumed as food. The total estimated fish production of the world in 2012 was 158 million metric tons with a per caput consumption around 19.2 kg. Similarly, the total estimated fish production of Nepal in 2013/14 was 64,900 metric tons with a per caput consumption of 2.3 kg.

II. Nutritive value
Fish is highly nutritious. It provides tasty, low calorie meal but is a good source of high quality protein. Fish is an almost zero-carbohydrate food, good for diabetes and other such patients. The protein content in fishes varies from 15-30% on wet weight basis and 60-80% on dry weight basis. The protein of fish is highly digestible and with well-balanced amino acids. Fish are low in fat and cholesterol. Fish is a good source of Vitamins- A, B and D and also offers a good source of calcium, iodine, fluorine, magnesium and zinc. Fish are rich in poly-unsaturated fatty acids containing Omega-3. Two poly-unsaturated fatty acids present in fish, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), collectively known as Omega-3, are essential fatty acids. They cannot be produced in human body, but are essential in the diet. These poly-unsaturated fatty acids can help to reduce the cholesterol level in the blood, thus minimize the risk of heart attack.

III. Medicinal value
Fish is low in fat, high in protein and an excellent source of Omega-3 fatty acids. Regular consumption of fish can reduce the risk of various diseases and disorders. Some research findings indicate the following:

Asthma: Children who eat fish are less likely to develop asthma.

Brain and eyes: Fish rich in Omega-3 fatty acids can contribute to the health of brain tissue and the retina of the eye. The IQ level of children whose mother consumed about 340 g fish per week during pregnamcy was found higher than non-fish eaters. Similarly, breastfed babies whose mothers eat fish have better eyesight, perhaps due to the Omega-3 fatty acids transmitted in breast milk.

Cancer: The Omega-3 fatty acids in fish reduce the risk of many types of cancers by 30 to 50 percent, especially of the oral cavity, oesophagus, colon, breast, ovary and prostate.

Cardiovascular disease: Eating fish every week reduces the risk of heart disease and stroke by reducing blood clots and inflammation, improving blood vessel elasticity, lowering blood pressure, lowering blood fats and boosting good cholesterol.

Dementia: Elderly people who eat fish or seafood at least once a week may have a lower risk of developing dementia, including Alzheimer’s disease.

Depression: People who regularly eat fish have a lower incidence of depression. Depression is linked to low levels of Omega-3 fatty acids in the brain.

Diabetes: Fish may help people with diabetes to manage their blood sugar levels.

Prematurity: Eating fish during pregnancy may help reduce the risk of delivering a premature baby.

Further, it is observed that different fishes are used as Ayurvedic medicines which help in treatment of duodenal ulcers, skin disease, night blindness, weakness, loss of appetite, cough and cold, bronchitis, asthma, tuberculosis, etc.

IV. Fish products
a. Fish meal: The dried and ground preparation of unused or trash fish is called fish meal and is a highly nutritive product that makes an excellent feed for poultry, pig, cattle and fish. Fish meal contains about 60-70% crude protein, 2-15% oil and 10-20% minerals. The protein of fish meal is highly digestible and contains all amino acids. It is also very rich in vitamins, calcium, phosphorous and iodine.

b. Fish oil: Fish oil is of two kinds, body oil and liver oil. The oil extracted from the whole body of the fish is called fish body oil. For the extraction of body oil, the fishes are minced, steamed, and then pressed for oil recovery, then subject to filter for refine. It is very rich in iodine. The fish body oil is mostly used in manufacture of paints, varnishes, soaps, lubricants, candle, printing inks, etc. It is also used in dressing of leather, tanning of skin and smearing the surface of boats for longer preservation.

The oil obtained from the liver of fishes is called fish liver oil. For the extraction of liver oil, livers are chopped and boiled in water. The oil is then skimmed out from the surface of the water and purified. Fish liver oil has medicinal value. It contains 55-75% fat and 5-10% protein. It is very rich in Vitamin A and D. Shark (Carcharhinus spp.) and Cod (Gadus callarius) liver oil are well known in pharmaceutical industries.

c. Fish silage: Fish silage is a liquid or semi-liquid product made from whole or part of the fish that are liquefied by the action of enzymes in the fish in the presence of an added acid (Hydrochloric or Sulfuric acid). The enzymes break down fish proteins into smaller soluble units, and the acid helps to speed up their activity while preventing bacterial spoilage. It is a highly nutritive animal feed. It contains about 15% protein; however, the composition of fish silage depends on the fish species from which it is made.

d. Fish flour: Fish flour is made up of dried and powdered fish. It is a superior quality of fish meal which is used for human consumption. It is considered an ideal protein source to supplement diet. It can be mixed with wheat or maize flour and used for enriching the nutritive value of bread, biscuits, cakes, etc. It is also known as hydrolyzed protein of fish.

e. Fish manure and guano: Low grade, unedible fish and offal from the fish-canning factories, fish-salting plants, fish-filleting plants and other fish processing industries are utilized to prepare the fish manure. These residues are dried, ground, mixed with ash and converted into manure, which contains a high percentage of nitrogen and phosphorous.

The word ‘guana’ means dung in Spanish language. Fish guano is prepared from the material left over after extracting oil from the fish. It has high content of nitrogen (8-10%), and has been found more effective than animal manure.

f. Fish glue: The gelatinous adhesive material obtained from the connective tissues of skin and bones of certain fish, principally cod fish, is called fish glue. It is used in gummed tape, letterpress printing plates, blueprint paper and adhering the wood, leather, glass, etc.
g. Isinglass: Isinglass is a substance obtained from the dried swim bladders of fish. It is a high-grade collagen used mainly for the clarification of wine, beer and vinegar. It can also be cooked into a paste for specialized gluing purposes. For making isinglass, the air bladder is removed from the fish, washed thoroughly and flattened by beating. The beaten pieces are then dried for the preparation of isinglass. It is in the form of shiny powder. Isinglass is generally made from sturgeon and cod fish.

h. Fish leather: The coarse scaly skins of several fishes (e.g., sharks and rays) are used for manufacturing, polishing and smoothing materials in place of sand paper. The dried and processed skin is also used for preparing high-quality shoes, moneybags, suitcases, belts, phone cases, etc. Fish leather is an eco-friendly alternative to the typical exotic leathers such as crocodile and snake that threaten endangered species.

The production of fish leather is a long and complicated process. For this purpose, skins from larger fish is collected and soaked in brine for a day then salted and again put in brine containing 10% hydrochloric acid. After that, skin is scraped on the surface and tanned by usual process. Actually, the exact details of the process are a closely guarded secret as only few manufacturers in the world are able to make it to a high standard after years of experimentation and fine-tuning.

i. Fish fin: The fins of the sharks and rays are used to make tasteful sauce and soups. It is a popular soup item of Chinese cuisine usually served at special occasions such as weddings and banquets, or as a luxury item in Chinese culture.

j. Fish caviar: Caviar is a high value fish product. It is a salt-cured eggs of certain species of fish such as sturgeon, salmon and trout. Traditionally the term caviar refers only to the eggs from some species of wild sturgeon in the Caspian and Black Sea. Depending on the country, caviar may also be used to describe the eggs of other fish such as salmon, trout, lumpfish and whitefish. Caviar is considered a delicacy and luxurious food and is eaten as a garnish or a spread.

For preparation of caviar, ovaries are first removed from the sedated female sturgeon and passed through a sieve to remove the membrane. Then the eggs are rinsed to wash away impurities. The eggs are then ready to become caviar by adding a precise amount of salt for taste and conservation. The fresh preparation is tasted and graded according to quality. Finally, the shiny eggs are packed into lacquer lined tins that will be further processed or sold directly to customers. It can be sold as fresh (non-pasteurized) or pasteurized, with pasteurization reducing its culinary and economic value. The price of caviar generally depends on age and species of the fish. For example, caviar of 60 to 100 years old Iranian beluga sturgeon costs about $35,000/kg. Caviar from salmon and trout are cheaper.

k. Fish pearls: The material obtained by scraping the silvery coating of the scales of certain fishes is used for polishing the hollow glass beds. These beds are then filled with wax and marketed as artificial pearls which are used as jewelry.

l. Fish insulin: Insulin is extracted from the pancreas of large sized fishes such as sharks. Prior to the introduction of biosynthetic insulin, insulin derived from sharks and other fishes was extensively used for glycemic control in human.

V. Biological control
Many species of carnivorous and larvivorous fishes prey upon insects and their larvae in water. These fishes can be used to control harmful insects, mosquito larvae, etc. Gambusia affinis is a well known fish for mosquito control, hence called mosquito fish. Other larvivorous species are Brachydanio spp., Rasbora spp., Puntius spp., Esomus spp., Colisa spp., Barilius spp., Chela spp., etc. They help in biological control of dengue, malaria, filaria, encephalitis, etc.

Similarly, the herbivorous species like grass carp (Ctenopharyngodon idella), tilapia (Oreochromis spp.), silver barb (Puntius gonionotus), etc. are used to control aquatic weeds and vegetations.

VI. Sports and games
Sport or recreation fishing is the fishing for pleasure or competition. Sport fishing can be done in a variety of ways. The most common form of sport fishing is done with a rod, line and hooks with baits, called angling. The most common sport fishes of Nepal are sahar (Tor spp.), asla (Schizothorax spp.) and rainbow trout (Oncorhynchus mykiss).

VII. Decorative value
Many species of colored fish are kept in aquarium, ocenarium, ponds and lakes for decoration or ornamentation. The common ornamental fish species kept in aquarium in Nepal are gold fish (Carassius spp.), gourami (Colisa spp.), zebra fish (Brachidanio spp.), guppy (Poecilia spp.), fighting fish (Betta splendens), koi (Cyprinus carpio), etc.

VIII. Employment opportunity
Fisheries and aquaculture sector provide, either directly or indirectly, a great employment opportunity for millions of people around the world. In 2012, about 500 million people were directly engaged in the world, part time or full time, in production of fish, either by fishing or in aquaculture. Fisheries and aquaculture sector in Nepal is relatively small, which provides employment to about 0.6 million people in 2013/14.