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Fish as a cheap source of protein, bioavailable minerals, vitamins and essential fatty acids, ensures global nutritional security. India witnessed around 14-fold increment in fish production from 0.7 million tonnes in 1950’s to 10.43 million tonnes in 2014-15. With a contribution of 5.05% to world’s capture production and 6.6% of total aquaculture fish production, India emerged as one among the most progressive fish producing countries in the world. Fisheries as a major agricultural sector, constitutes 0.92% of total GDP and 5.58% of total agricultural GDP of India. With the global fish export value of 148,147 million USD, India ranked seventh position among the top fish exporters of the world. The sector is crucial in securing food supply, job opportunities, nutritional needs and earning foreign exchange for the country, cataloguing it as a sunrise sector of Indian economy.

Technological developments in harvest sector

Introduction of new materials for fishing gears, mechanization of fishing crafts and modern electronic technologies for navigation and fish location, paved way for the significant increase in fish production in India over the years. ICAR-CIFT, Cochin has been involved in the design and optimization of a range of crafts and gears since its inception, which gave a major fillip to the harvest sector of Indian fisheries. Considering the plateauing/decline in catches perceptible since last two decades, ICAR-CIFT has shifted its focus from increasing production to responsible harvest of resources. As a result a large number of technologies for sustainable harvest and green technologies with reduced emissions were developed.

Finfish and aquatic invertebrates are part of Fish Genetic Resources (FiGR) that has actual or potential value for culture and capture fisheries. Fish as a group, have the highest species diversity among all the vertebrate taxa. Out of 62,305 species of vertebrates recognized world over, 32,064 (~ 52%) are valid fish species; of which, the great majority (97%) are bony fishes, mainly teleosts; and the remaining (3%) are cartilaginous fishes (sharks & rays) and jawless fishes (lampreys and hagfishes) (Eschmeyer and Fricke, 2012). India is blessed with vast fishery resources, like exclusive economic zone (2.02 m sq. km), coast line (8,129 km), ponds and tanks (2.254 m ha), beels, ox-bow lakes and swamps (1.3 m ha), reservoirs (2.90 m ha), rivers and canals (173,287 km), brackish water (1.235 m ha) (Ayyappan et al., 2011). The country is fortunate to possess vast and varied fish genetic resources in different aquatic ecosystems and being home to 7.84% of global finfish diversity, with 3535 species of fish, of which 3035 are native species, representing 46 orders, 252 families and 1,018 genera. The 500 exotic fishes are also covered and majority of them are of ornamental fishes. Out of the 3035 native fishes, 1016 are freshwater, 113 are brackish water and 1906 are marine species and at least 258 species are of commercially important (NBFGR, 2016-17). India harbours a rich diversity of fishes and four out of 34 biodiversity hotspot areas of the world. The biodiversity hotspots i.e. the Western Ghats and North East India harbours maximum endemic freshwater fishes. The Western Ghats harboring about 306 finfishes out of which nearly 69% are endemic to the region (Gopalakrishnan and Ponniah, 2000). Likewise North East India, another biodiversity hotspot area, harbors about 240 fin fishes and nearly 40% are endemic to the region (Sarkar et al. 2012). In the past one and half decades more than 50 new species were described from these areas and more than 10 new species were described from the marine environment.

Aquaculture or farming and husbandry of aquatic organisms and plants is the future for increasing aquatic food production. It is the fastest growing food production sector with an annual average growth of >6% in the last two decades. It increased from <1 million tonne in 1950 to 70.2 million tonnes in 2013. An update of aquaculture production (FAO) revealed that the total world aquaculture production continued to grow in 2013, reaching 97.2 million tonnes (live weight) with an estimated value of US$157 billion. A total of 575 aquatic species and species groups are grown in freshwater, seawater and brackish water have been registered in the FAO Global Aquaculture Production Statistics Database. The production of farmed food fish (finfish, crustaceans, molluscs and other aquatic animals) was 70.2 million tonnes in 2013, up by 5.6 % from 66.5 million tonnes in 2012. The production of 27 million tonnes of farmed aquatic plants was a 13.4% jump on the 23.8 million tonnes of 2012. The contribution of aquaculture to the world total fish production reached 43.1%, up from 42.1% in 2012. It was only 30.6% a decade ago in 2003. Meanwhile, world production of aquatic plants, mostly seaweeds, is still overwhelmingly dominated by aquaculture (95.5% in 2013). On a global scale, the production of major non-fed species contributed 30.7% to world food fish aquaculture production in 2013, including 13.9 million tonnes of bivalves and 7.7 million tonnes of filter-feeding carps.

Mariculture involves the cultivation of marine organisms for food and other products in an enclosed section of the sea (cages/pens), or in tanks, recirculating systems, ponds or raceways in seawater..It is a promising sector by which the additional marine fish requirement can be met in the future years. It is also the fastest growing sub-sector of aquaculture. At global level, mariculture produces many high valued finfishes, crustaceans and molluscs viz. oysters, mussels, clams, cockles and scallops. In 2013 mariculture has contributed around 25.5 million tonnes of foodfish globally which formed about 36.3 %of the foodfish aquaculture production(World food fish aquaculture production was 70.2 million tonnes in 2013). Molluscs dominated the global mariculture production (59.7%) followed by finfish (22.7%), crustaceans (16.2%) and others (1.4%). In addition about 26.9 million tonnes of macro algae were also produced by mariculture. The total mariculture production including seaweeds was 52.4 million tonnes in 2013 which constituted 53.9% of the total aquaculture production (The total global aquaculture production including the aquatic plants was 97.2 million tonnes in 2013).

The History of Fish Keeping

Philip Henry Gosse (1810-1888) coined a term “Aquarium” which is now familiar to all of us, in his 1854 book The aquarium: An unveiling of the wonders of the deep sea.

The idea of keeping aquariums can be dated back to 2500 BC and has evolved into a complex hobby that exists today. Ancient Sumerians and Romans kept fish in containers as early as 2500 BC, similar to what we now know as fish tanks. These tanks were designed to keep fish alive long enough to prepare the specimen for food. It is also known that Romans and Babylonians kept ponds filled with fish for ornamental use (History of Fish Keeping as a Hobby).

As time progressed, the art of fish keeping became a “luxury for the rich” (DuHammel 1). Many people consider the Chinese as being the most important contributors to the hobby. “By 1136 AD Emperor Hiau-Tsung started to breed and keep these fish in a more controlled environment. Several new breeds of ornamental fish ornamental emerged.” (DuHammel 1). As more people became involved in the idea of fish keeping, having a goldfish was no longer an indicator of a person’s status. Many common people began to keep goldfish; the fish that they kept represented a good luck charm.

India is situated north of the equator between 8°4' and 37°6' north latitude and 68°7' and 97°25' east longitude, is the largest peninsular country in the world bordered by Arabian Sea in the west, Indian Ocean in the south and the Bay of Bengal in the east. India has a coastline of 8118 km and 0.5 million t sq. km continental shelf endowed with 2.02 million sq. km of Exclusive Economic Zone (EEZ). It has a catchable annual fisheries potential yield of 4.41 million occupying third rank in world marine fish production (Table 1). India’s territorial waters extend into the sea to a distance of 12 nautical miles from the coast baseline. The vital details on marine capture fisheries of India are given in table

Netting yarns for the fabrication of fishing gear are either of textile or non-textile origin. Textile materials compose of netting, twine and rope while non-textile origin materials constitute floats, sinkers, hooks etc. Raw material for fish netting consists of fibres which can be distinguished into two groups: natural fibres and man-made fibres. Different kinds of fibres originating from plant and animal body parts have been used for production of textiles and other products and are termed as natural fibres. Natural fibres such as cotton, manila, sisal, jute and coir were the materials exclusively used in earlier days for fishing gear fabrication.

Later, the invention of polymers resulted in synthetic fibres the use of which revolutionalized the fishing industry. In recent decades advances have taken place in fiber technology, along with the introduction of other modern materials. With the introduction of man-made synthetic fibers in India in the late 1950s, natural fibers used for the fishing gears have been substituted by these synthetic materials due to their high breaking strength, low maintenance cost, long service life and better uniformity in characteristics. Most important synthetic fibres used in fisheries are polyamide (PA), polyester (PES), polyethylene (PE) and polypropylene (PP). Other synthetic fibres, which are less widely used and generally restricted to Japanese fisheries, are polyvinyl alcohol (PVA), polyvinyl chloride (PVC) and polyvinylidene chloride (PVD). Earlier, netting used to be fabricated manually, which is laborious and time consuming while the introduction of synthetic fibres paved way for machine made nettings which are almost exclusively used in fishing net fabrication.

Bottom or demersal trawling continues to be one of the most important fishing methods of the world. In India more than 35,230 trawlers of various sizes ranging from 9 to 30 m L_OA with engine power ranging from 45 to 495 hp @ 2000 rpm are in operation. Trawl is a bag net towed through water to filter out fishes, the mouth of which is kept open horizontally by means of a beam or otter boards and vertically by means of floats and sinkers. Horizontal mouth opening is also effected by dragging the net from two boats known as bull trawling or pair trawling. The principle of trawling is the movement of the net under water filtering the water through the mesh in the netting, without either permitting the fish to escape or gilling them (Fig. 1). Trawl net is fabricated using polyethylene netting after cutting and shaping the panels as per the design

The 20^th century had seen unprecedented increase in fishing capacity; in terms of the vessel number, increase in size of the vessels and advances in the electronic and navigational equipment coupled with easily manufactured and durable fishing nets. The effect of these innovations sequentially, was the burgeoning in the fish production, plateauing of catches and the myth of inexhaustibility of fishery resources in the sea was proven wrong. A large number of stocks world over have declined and the stock status of many are now alarming, but still the trend towards larger, more powerful and faster vessels continues.

Global fisheries production has reached a plateau and is now hovering around 80 million tonnes during the last decade. It is also noted that the status of world’s marine fish stocks have not improved overall. About 31.4% of assessed fish stocks are fished at a biologically unsustainable level and therefore overfished. Fully fished stocks accounted for 58.1% and underfished stocks 10.5%. It is evident that most of the stocks are fully fished with no further potential for increase in production.

The importance of reducing bycatch and minimizing ecological impacts of fishing operations has been emphasized by scientists and fishery managers and recognized by fishermen. Trawl fisheries in different parts of the world are now being required to use bycatch reduction devices as result of pressure from conservation groups and legal regimes introduced by the governments. The Code of Conduct for Responsible Fisheries (FAO, 1995), which gives guidelines for sustainable development of fisheries, stresses the need for developing selective fishing gears in order to conserve resources, protect non-targeted resources and endangered species. Although the problems of using non-legal gears and designs often with smaller mesh sizes are reported. Most of the problems due to generation of bycatch and damage to the ecosystem function, has been implicated due to trawling.

Quality of fish raw material plays an important role for the quality of the end-product. Once the fish raw material freshness and nutrition value is lost, it cannot be recovered in the processing stages. Products that are processed from low quality raw material are not always a safety risk, but the quality (nutrition value) and shelf life is significantly decreased. The quality deterioration can start right away during fishing and it continues all the way to the final user. Time-temperature abuse should be avoided at all stages of handling till landed fish reaches the consumer or the processor. In tropical countries more care in handling is necessary as fishes thrive in high ambient temperature has high body temperature and hastens spoilage.

Fish is highly perishable because of their chemical composition. It has high content of soluble substances in the flesh (many of which contain nitrogen and triglycerides characterized by polyunsaturated fatty acids) and high level of autolytic enzyme. After the death of the fish, spoilage starts due to the action of microbes, enzyme and oxidation. It is therefore, necessary to preserve fish after harvest if not consumed or disposed immediately.

Maintaining the quality of fish begins with harvest and carries through the harvest-to- consumption chain. Careful handling of fish and shellfish while harvesting and during transport to the processing plant is critical if the high quality of the product is to be maintained. There are, however, several constraints on handling the fish; the important among them are the bacteriological, chemical and physical processes that cause degradation of fish. The surface of dead fish is an ideal growth habitat for bacteria and the end result of such activity is spoiled fish. Reduction of temperature can prevent the growth of many bacteria that cause the spoilage. Chemical breakdown due to oxidative and enzymatic reactions can lead to off odours and flavours and rancidity. Digestive enzymes can initiate decomposition in the dead fish. Physical factors can enhance the bacteriological or chemical processes: bruising, tearing, cutting etc. can expose fish muscle to more rapid bacteriological growth, cause internal bleeding which darkens the fillets and expose greater surface area for chemical oxidation.

Since fish is a highly perishable item of food, it has to be immediately processed to various products to preserve the quality and to increase the shelf life. Fish requires proper handling and preservation to increase its shelf life and retain its quality and nutritional attributes. The objective of handling, processing and preservation is to control or reduce the spoilage process so that the final product is wholesome and safe for the consumer. Fish and fishery products brought to market in a well-preserved condition will generally command higher prices, both at wholesale and retail levels, and thus give better returns to the fishing operation.

Low temperature preservation by chilling and freezing methods are widely practiced to maintain the quality and freshness of fish and fish products. Chilled storage method, i.e., keeping the fish in the unfrozen condition has only limited shelf life and it will vary between 4 and 20 days depending on the condition and species of fish. In frozen storage also the shelf life is restricted but it varies from few weeks to years. The various factors that affect the frozen storage shelf lives are condition of fish at the time of catch, handling, processing and product development, packaging and glazing of the product, freezing method adopted, frozen storage temperature, stacking methods and transportation techniques. These factors can be put together and can be termed as ‘Product, Processing and Packaging’ (PPP) and ‘Time Temperature Tolerance’ factors (TTT).

Thermal processing also known as heat processing is commonly used processing method which helps in extending the shelf life of the food productswith high safety level, convenience and a healthy product.Seafood as a whole food is highly nutritious. Benefits to human health associated with the consumption of seafood is well recognized for multiple bodily organs and physiological functions but their high perishable nature is a concern. Seafoodundergoes spoilage due to autolytic, microbial action as well as oxidation of lipid. Proper handling and preservation is essential to maintain quality of fish. Heat processing is an age old preservation method practiced in many countries to extend the shelf life of food products. Heat treatment causes the destruction of microbes which increases the shelf life. There are number of thermal processing operations like- baking, blanching, canning, dehydration, extrusion, frying, pasteurization, sterilization, etc. All these operation serves various purposes and helps in manufacture of different food products.

Thermal processing is of utmost importance to low acid high water activity foods, where there are no hindrances to microbial growth. The proper delivery of heat is essential to cause the destruction of microbes to avoid food spoilage. In seafood’s processing, thermal processing through canning (retort pouch processing) is a common approach. In canning, the food is preserved by application of heat in hermetically sealed cans (pouches). Hermetic sealing means- complete airtight sealing. This prevents contamination from outside. Heating at very high temperature ranging from 110 to 135⁰C for a desirable time helps in killing all the vegetative forms of microorganisms as well as most heat resistant microbial spores. The amount of time needed for processing is different for each food type depends on hurdles present in the food and heat transfer characteristics. In thermal processing of seafood products, heat processing is aimed for the destruction of spores of Clostridium botulinum. A number of thermally processed ready-to-eat (RTE) products are available on market shelf.

Food processing involves the transformation of raw materials into consumer-ready products, with the objective of stabilizing them to prevent negative changes in quality and ensure food safety. To consumers, the most important attributes of a food product are its sensory characteristics like texture, flavour, aroma, shape and colour. The aim of food manufacturers is to develop and employ processing technologies that retain or create desirable sensory qualities or reduce undesirable changes which take place during processing. Alternative or novel food processing technologies are being explored and implemented to provide safe, fresher-tasting, nutritive foods without the use of heat or chemical preservatives. The major non thermal technologies gaining importance are High-pressure processing, Pulsed light technology, Pulsed electric field, Irradiation etc.

High pressure processing

The application of very high pressures (upto 87,000 psi, 6000 bar or 600 MPa) for preservation of food substances in combination with or without heat is known as high pressure processing (HPP). This process is also known as high hydrostatic pressure processing (HHP) or ultra-high pressure processing (UHP). When compared to thermal processing, pressure treated foods have a fresher taste, better appearance, texture and nutritional value. High pressure processing can be conducted at ambient or refrigerated temperatures, thereby eliminating thermal effects and cooked off-flavors. The technology is highly beneficial for heat sensitive products. The first high pressure processing line was introduced in Japan for jam manufacture in 1990’s and has since been upgraded to several food products. A number of HPP products have been commercialized in North America, Europe and in China. Machines are now available with operating pressures in the range 400-700 MPa and capacities ranging up to 900 kg per batch. Since HP processing affect mainly the non-covalent bonds of the food, the quality characteristics of foods such as color, flavor and nutrients generally remain unaffected (Knorr, 1993).

Smoking is an ancient method of food preservation, which is also known as smoke curing, produces products with very high salt content (>10%) and low water activity (~0.85). Smoking is a process of treating fish by exposing it to smoke from smouldering wood or plant materials to introduce flavour, taste, and preservative ingredients into the fish. This process is usually characterised by an integrated combination of salting, drying, heating and smoking steps in a smoking chamber. The drying effects during smoking, together with the antioxidant and bacteriostatic effects of the smoke, allow smoked products to have extended shelf-life. Smoked seafood includes different varieties like, smoked finfish and smoked bivalves. Many of the smoked products are in the form of ready-to-eat.

Developments of modern food preservation technology, such as pasteurization, cooling/refrigeration, deep-freezing, and vacuum packaging, have eclipsed the preserving functions of many traditional methods including smoking. Nowadays, the main purpose of smoking has been shifted for sensory quality rather than for its preservative effect.

Depending upon how the smoke is delivered into the food and smoking temperature, four basic types of smoking can be defined: hot smoking, cold smoking, liquid smoking, and electrostatic smoking. Hot smoking is the traditional smoking method using both heat and smoke, which usually occurs at temperatures above 70 °C. For smoked fish and fishery products, a minimum thermal process of 30 min at or above 145 °F (62.8 °C) is required by FDA (2001). Therefore, after hot smoking, products are fully cooked and ready for consumption.

Pre-processing of fish

Fish is a highly perishable food which requires proper handling and preservation to increase its self life and retain its quality and nutritional aspects. Therefore, fish pre-processing and preservation are become a very important part of commercial fisheries. Preservation means keeping the fish after landing in a condition of wholesome and fit for human consumption for a particular period. This preservation should cover the entire period from the time of capture of fish to its sale at retailer’s counter. The main aim of processing and preservation of fish is to prevent fish from deterioration. Methods which are commonly used to preserve fish and fishery products include the control of temperature using ice, refrigeration or freezing and control of water activity by drying, salting, smoking or freeze-drying etc (FAO, 2011). Fish has to be pre-processed in such a manner that it remains fresh for a long time with a minimum loss of flavour, colour, taste, odour, nutritive value and digestibility. Fish processing can be subdivided into fish handling which is the preliminary processing of raw fish and the manufacture of fish products.