Fish byproducts

Most of the captured fishes are utilized as food in fresh condition, while several others are distasteful and considered unsuitable for human consumption. Similarly, the materials discarded during fish processing  .Such  inedible fishes and discarded fish materials form  materials for fish by-product industries. Some of the economically important  byproducts produced from Fishes  are the following.

a. Fish meal

Fish meal is prepared either from the whole fish or from the fish waste collected from markets and fish oil manufacturing units. The nu- trients of fish meal include 6-l2% moisture, 50-70% protein, 2-15% fat, 10-20% minerals and a variety of vitamins. Proteins of fish meal have high digestibility and biological values. The fish meal is rich in calcium phosphorus and appreciable amounts of iodine. Vitamins A, D, E and Kare present in some meals. Vitamin B 12, which promotes growth in animals, is the predominant vitamin in fish meal. The other B complex vitamins include thiamine, riboflavin, nicotinic acid, pantothenic acid, pyridoxine, choline and inositol. High grade fish meal is used as an in~ gredient of the feed of farm animals, such as fish, duck, chicken, pig, etc. Low grade fish meal is used as manure. For producing fish meal the fish and/or their wastes are ground well and the resultant product is steam cooked and pressed for the removal of water. The cake thus formed is packed and marketed as fish meal.

b.Fish Oil : The most important fishery by-product industry is that of the fish oil, which is of two kinds-liver oil and body oil. The oil extracted from the whole body of the fish is called fish body oil, whilethat obtained from the liver of certain fish is called the fish liver oil. Liver oil contains vitamins A and D, while the body oil contains them in traces only. The refined oil from the liver of fishes has a medicinal use, being the source of vitamins 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% lat, 5-10% protein and the rest water, and is of considerable medicinal value.

c. Fish protein concentrate (F PC)-Fish is esteemed for its highly digestible, superior quality proteins. For preparing fish protein concentrate, protein from the flesh is extracted in its purest form, free from fat. A good quality FPC is a fine white powder, with high protein content (80—9O%) and less than 1% fat. It is free from fish odour and has a bland taste. FPC of. desired nutritional quality forms an excellent supplement to the human diet. High grade FPC is used as a substitute for egg albumin in baking cakes and icecreams. It is also used as an ingredient in some pharmaceutical products.

d. Isinglass (fish maws) Isinglass is a high grade collagen, produced from the air (swim) bladder of some fishes, such as eels, catfishes, carps and thread fins. For preparing isinglass, air bladders are thoroughly washed, their black outer cover is scrapped off and then dried. Then, they are soaked in water, cut into pieces of required size and pressed. They are again dried and marketed. Isinglass is used primarily for the clarification of beverages. It also finds use as an adhesive base in confectionery products and Indian ink, and as an adhesive for glass, pottery and leather. It is a good substitute for gelatin. 

e.Biochemical and Pharmaseutical compounds:A variety of materials, such as nucleic acids, nucleosides, protamine,insulin, strepogenine, cortisone, glutathione, bile salts and proteolytic enzymes, have been isolated from various tissues and organs of fishes. However, only protamine and insulin have been produced on a commercial scale. Protamine, in combination with insulin, forms a suitable compound for the treatment of diabetes. Protamine slows down the action of insulin and thereby prolongs the effectiveness of insulin. Protamine is found in the sperms of various fishes. Insulin is found to be associated with the gall bladder or bile duct of fishes and therefore it can be easily isolated in high purity and high concentration. Further more, insulin from fishes normally remains stable even after the death of the fish. Tunas and bonits are the most suitable fishes for the extraction of insulin.

f.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 by spreading them on the beach. The dried fish is ground and converted to manure, which contains a high percentage of nitrogen and phosphate. The head, tail and body shell of prawn is used to prepare prawn manure and contains about 6% nitrogen and 3.49% (phosphate with an appreciable amount of lime. Fish guano is prepared from the material left over after extracting oil from the fish. Mostly sardines are used for preparing fish oil and the waste material forms the fish guano. It contains 8.9% nitrogen and phosphate, and when mixed with soil, forms a rich fertilizer for plants. It is several times richer than ordinary cattle manure.