Fishes form one of the most important group of vertebrates for man, influencing his life in various ways. Millions of human beings suffer due to hunger and malnutrition, and fishes form a rich source of food and provide a means to tide over the nutritional difficulties of man. In addition to serving as an important item of food, fishes provide several byproducts to us. Fish have considerable economic importance are useful as well as harmful to man.
Useful Fishes:
1. Fish as Human Food:
Fish have formed an important item of human diet. Nearly all fish freshwater and marine are edible and have been an important source of protein, fat and vitamins A and D since time immemorial. In most fishes, the flesh is white, contains about 13 to 20% of protein and has a food value of 300 to 1600 calories per pound.
According to Pottinger and Baldwin, fish meat contains atleast 5 of the essential amino acids. Besides this, it contains vitamin A and D together with large amount of phosphorus present in it. Important marine fishes include salmon, cod, halibut, herring, eels, tuna, mackerel, and sardines. Important freshwater food fishes are cat fish, trout, bass, perch and mullet. Even eggs of certain fishes, such as Russian sturgeon are eaten as cavier.
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The major food fishes of India include Labeo, Catla, Cirrhina, Mystus Wallago, Notopterus, Ophiocepholus, etc. The cartilaginous sharks, skates and rays are also used as human food in several countries. They are eaten by poorer classes of people living along the sea coasts of India and Sri Lanka. The canned meat of sharks is sold commercially under the name of gray fish. In south-east Asian countries, shark fins are dried and boiled to get a gelatinous material used as soups.
Fresh fish meat is usually cooked for human consumption. However, large quantities are refrigerated, salted, smoked, canned or pickled. Today, fisheries of the world carry on business worth several hundred thousand rupees annually and also provide employment to thousands of people.
2. Fish as Food of Cattle:
The scrap from canneries, as well as entire fishes that are not relished by man, are dried and ground in mill. This is called fish meal and is used as artificial food for poultry, pig and cattle. Fish meal is produced in several states like Maharashtra, Andhra Pradesh, Tamil Nadu, Bengal and Kerala chiefly from sardines, meckerels, ribbon fish, etc. The fish is first cooked in large pots containing sufficient quantity of water, on fire or on steam.
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The cooked material is then pressed to remove moisture and dried in the sun on suitable platforms. The resultant product is then stored, and if preserved in airtight containers after sterilisation retains its nutritive value for a long time.
The fish meal contains about 60% protein and high percentage of calcium phosphate so that it is very valuable for cattle and poultry. The manufacture of fish meal can be undertaken as a cottage industry requiring little expenditure.
3. Fish Manure:
Fish that are unfit for human consumption are used to prepare fish manure for the fields. During peak season, when there is a large supply of fish, or they are landed in spoiled condition, they are sun dried on the beach. The dried fish is ground and converted to manure, which contains a high percentage of nitrogen and phosphate.
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Mostly sardines are used for preparing fish meal and the waste material forms the fish guano. It contains 8.9% nitrogen and phosphate, and when mixed with soil, forms a rich fertiliser for plants. It is several times richer than ordinary cattle manure.
4. Fish Oils:
The most important fishery by-product is that of the fish oil, which is of two kinds- body oil and liver oil. The oil extracted from the whole body of the fish is called fish body oil, while that obtained from liver of certain fish is called the fish liver oil. Liver oil contains vitamin A and D, while the body oil contains them in traces.
The refined oil from the liver of fishes has a medicinal use, being the source of vitamin A and D. The body oil from fish has many uses, such as in painting, varnishing, soap, candle, leather and steel industries. For preparing body oil, fish are boiled in large quantity of water. Oil is removed quickly and washed in boiling salt water.
Liver oil is prepared from the liver of several species, including sharks and rays. Oil is extracted from the liver soon after the fish are caught to avoid action of enzymes. Liver is cut into small pieces and boiled in sufficient quantity of water. Oil is skimmed from the surface of water and sent for purification. Liver oil contains 55-75% fat, 5-10% protein and the rest water. It is of considerable medicinal value.
5. Fish Skin and Leather:
The skin of several fishes like the sharks and rays are used for making polishing and smoothing material. Shark skin leather is of some commercial importance in the manufacture of many useful articles such as shoes and hand bags, etc. In Japan, lantern are prepared from the skin of puffer fishes (e.g., Tetrodon). Some tribal people used skins of puffer and porcupine fishes {e.g., Diodon) for war helmets.
Crude skins of sharks and rays are used by carpenters and metal workers. Shark skin tanned with placoid scales on it is called shagreen. It has been used as an abrasive for polishing wood and ivory and also for covering jewel boxes, fine books and sword handles.
6. Fish Glue:
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Liquid glues are prepared from skin, head and other trimmings of certain fishes. This glue has an adhesiveness of great power for paper, wood, leather and glass.
7. Isinglass:
It is a gelatinous product obtained from the air-bladders of certain fishes such as sturgeons, carps, perches, salmons, cat fishes, cods, etc. The isinglass is a shining powder and is used for clearing wine, beer, making edible jelly and in the preparation of adhesive material.
The air-bladder is removed from fish, washed in cold water and flattened by beating it on a piece of wood. The bladder is then dried in the sun, and is exported for the preparation of isinglass. The finest quality of isinglass is obtained from Russia.
8. Fish Fin:
The fins of sharks are exported to China where they are used for preparing soup.
9. Medicines and Disease Control:
The refined oils extracted from livers of cods and sharks are rich in vitamins A and D. Pituitary glands yield important extracts for medicines. Fishes like top minnows {Gambusia affinis), Trichogaster, Chela, Puntius, Barilius, Danio, Colisa, Rasbora, Esomus, Ambassis, Aplocheilus, Barbus, Panchax, etc., feed voraciously on mosquito larvae.
These larvicidal fishes are propagated and distributed widely into ponds, lakes and tanks to destroy mosquito that transmit malaria, yellow fever and other dreadful diseases of tropical countries. Certain fishes and their bye-products contribute to useful Ayurvedic and Unani medicines for treatment of duodenal ulcers, skin diseases, night blindness, general weakness, loss of appetite, colds, coughs, bronchitis, ashthma, tuberculosis, etc.
10. Sports and Recreation:
Sport fishing by individuals and fishing parties is a popular recreation of million of people, as well as a source of food, all over the world. The most commonly hunted fishes are the freshwater perch and trout and the marine tarpon. However, some of the best game fish is most famous for sport that it provides, but its flesh is not palatable.
Many people’s hobby is to cultivate certain tropical fishes as pets. Both native as well as foreign fishes are displayed in home aquaria for their beauty and graceful movements. Common aquarium fishes are gold fish (Carassius auratus), angel fish (Pterophyllum), sword tail guppy (Xiphophorus), minnow (Gambusia affinis), siamese fighter (Betta splendens), paradise fish (Macropodus), Hemigrammus, Aphyocharax, loach (Botid), Trichogaster, Tilapia, etc. Goldfish cultured and not found in nature and the Japanese have produced their several curious artificial varieties. Pet shops now-a-days stock many kinds of fishes for hobbyists and scientists.
11. Fancy Articles:
Scales of garpike (Lepidosteus) are used for jewelry and novelties. From scales of some fish is secured a pigment whose water suspension is known as pearl essence. It is used in the manufacture of artificial pearl in Europe, especially in France.
12. Scientific Study:
Fishes have considerable use as experimental animals, especially in the fields of Genetics, Embryology, Animal Behaviour and Pharmacology. Certain fishes such as Latimeria and dipnoans have anatomical features of great zoological interest. Fishes like dogfish (Scoliodori), perch (Perca) and carp (Labeo), etc., are dissected for anatomical study in zoological laboratories. Researches in ichthyology are conducted for the benefit of fisheries and mankind.
13. Industries:
As the fish forms a rich source of food, millions of people are engaged in fishing industry and depends on fisheries for their livelihood in various ways. Besides those who directly catch the fish for marketing, there are equally large number of people engaged in subsidiary industries like refrigeration, preservation, canning, and in the manufacture of fish products and by-products.
Harmful Fishes:
1. Destructive:
All the cartilaginous fishes are predaceous and feed chiefly on large quantities of crabs, lobsters, squids and other valuable marine animals. They cause great harm by destroying eggs, young and even adults of our food fishes. Sharks are extremely dangerous in the sea and injure fisherman and damage their nets, steal baits, devour captured fish and drive away squids and fishes to be netted. The damage done by these sharks amounts to several hundred thousand rupees.
2. Injurious:
Some larger sharks and sword fish may capsize small boats and injure or even kill fisherman. All sharks, small or big, are a menace to bathers and skin divers in shallow waters. The pirhanas of Central and South America have very strong teeth and are dangerous even to man.
Some fishes like cartilaginous electric ray (Torpedo) have electric organs which give powerful shocks to swimmers and fishermen. An extreme case of specialisation is the bony electric eel (Electrophorus electricus) of the Amazon. It is nearly 1.5 metres long and the postero-ventral four-fifth part of the body is occupied by the electric organ. It can generate electricity up to 600 volts in potential with a maximum output of 1000 watts. Carnivorous fishes eat away the larvae of useful insects.
3. Poisonous:
Poisonous glands are found in many cartilaginous fishes such as sting ray (Trygon) and eagle ray (Myliobatis). They can inflict painful wounds, sometimes fatal by the poisonous stings or spines. Poisonous glands are also found in Squalus (dogfish), Heterodontos, Chimaera, Diodon (porcupine fish), Tetrodon (globe fish), scorpion fish, etc. These are also capable of causing wounds by their spines or spiny opercula. Flesh of some tropical fishes (e.g., Tetrodon) is also poisonous and may prove fatal to man.