Introduction

Fish and fisheries contribute substantially to local food consumption, livelihood, and export earnings of countries. The quantity of fish produced from different sectors has been increasing over the years and the growth is much higher for the developing countries. There was an increase of over 42 percent in the global fish production from both capture and aquaculture sectors over the last two decades reaching total of 179 million tonnes in 2018.  Aquaculture contributed 95 percent to this increase.

The per capita availability of fish as food has increased from 9.0 kg (live weight equivalent) in 1961 to over 20.0 kg in 2018, at an average growth rate of 1.5 percent per year (FAO, 2020). The rise in the total fish production, is due to a combination of different factors, in the value chain in terms of policy interventions, infrastructure development, reduction in losses, and due to the increasing purchase power.  It is estimated that globally in 2017, fish accounted for 17 percent of the total animal protein and, 7 percent of all proteins. This contribution of fish to the total animal protein is about 50 % in countries that lack other source of proteins and small Island developing States.

It is estimated that globally about 35% of the fish from capture and aquaculture is either lost or wasted every year and this is a serious issue, which has garnered much interest in research, policy, and implementation. Fish losses is mostly due to the inefficiency in the value chain and key issues being the lack of infrastructure, services, and access to suitable markets. Most of the studies related to losses in fisheries, addressed the physical losses while those related to the loss in quality of fish due to inefficiencies in the value chain are limited (Kruijssen et al., 2020). Globally, the total waste in terms of discards, between 2010 and 2014, in marine fisheries has been estimated as 9.1 million tonnes, with values ranging from 6.7 to 16.1 million tonnes, depending on the fisheries (Roda et al., 2019).

The total number of fishing vessels in 2018 was estimated at 4.56 million, which showed a decline of 2.8 percent compared to 2016. Asia with a total number of 3.1 million vessels, contributes about 68% of the total and 75% of these vessels are motorized (FAO, 2020).

Due to the prevalence of tropical shrimp trawling that contributes significantly to the discards, countries in South Asia have significant quantities of discards. India, which has one of the largest number of trawlers (35,228) operating in the region has adopted many technical measures such as seasonal closures and gear-based restrictions to improve the deteriorating state of marine fisheries (CMFRI,2012).

The countries in South Asia contribute about 10% of the global production and about 3.7% of the total trade in fish and fishery products. The countries in the region also show wide variation in the per capita availability of fish, with average protein from fish availability at 41.4 g/capita/day for Maldives, which is one of the highest and 0.065 g/capita/day for Afghanistan, which is one of the lowest, when compared to the global average of 5.6 g/capita/day (FAO, 2020).

Role of fish in Nutrition

Fish, including crustaceans and molluscs   play a major role in human nutrition by providing at least 20% of protein intake for a third of the world’s population. The importance of fish in the human diet and its beneficial effects has been proven in terms of food security as well as in combating under nourishment and micronutrient deficiencies in developing countries (Kawarazuka & Béné, 2011). World trade of fish for human consumption is projected to total 45.8 Mt live weight by 2028, up 11% on the 2016-18 base period. Exports of fish for human consumption are expected to concentrate in fewer exporting countries. Live, fresh or chilled is often the most preferred and highly priced form of fish and represents the largest share of fish for direct human consumption (45 %) followed by frozen (31 %), prepared and preserved (12 %) and cured (dried, salted, in brine, fermented smoked) (12 %). Freezing represents the main method of processing fish for human consumption; it accounted for 56 % of total processed fish for human consumption and 27 % of total fish production (FAO, 2018).  Throughout the world, post-harvest fish losses are a major concern and occur in most fish distribution chains; an estimated 27 % of landed fish is lost or wasted between landing and consumption. When discards prior to landing are included, 35 % of global catches are lost or wasted and therefore not utilized (Gustavsson et al., 2011). Climate change, weather variability and changes in the frequency and extent of extreme weather events are anticipated to have a major impact on the availability and trade of fish and fish products mainly through habitat destruction, changes in fish migration patterns and natural productivity of fish stocks.

Fish contains macro and micro elements, which are very vital for human health. Calcium in fish contributes to vital roles in human body viz maintaining required calcium level in blood, bone and cells and also for the proper secretion of hormones like insulin. Children, pregnant and lactating women require large amount of calcium and phosphorous, which can be met from sufficient consumption of fish. The role of phosphorous at cellular level is immense as in the production of energy through ATP or in activation of enzymes and cell signaling molecules by phosphorylation. Apart from calcium and phosphorus, fish is rich in Sulphur, potassium and magnesium. Fish contain significant amount of phosphorus which is essential for the above-mentioned vital body functions. Sulphur is a component of amino acids, cystine, methionine and B vitamins thiamine and biotin. Potassium plays a key role in electrolyte balance, maintains membrane potential. Magnesium is an element which is part of more than 300 metabolic reactions in the body. Iron deficiency can alter metabolic processes adversely leading to anaemia especially in children, lactating and pregnant women. Many varieties of fish are good source of iron and copper. For iron absorption in the body, copper plays a significant role, it is also necessary for hematologic and neural functions. Zinc is another micronutrient essential for the body functions, nearly 100 enzymes depend on zinc for their reactions. Its role varies from cell replication, protein synthesis to wound healing. Fish is considered as a delivery source for Zn and Mn.  Cobalt, chromium, selenium and nickel are other micronutrients in fish, whose beneficial roles in human body have been well established. Identified protein rich, oil rich and micronutrient dense fish species could be utilized in community nutrition programs like ‘mid-day meal’ program in operation in schools in countries like India. Such species include Anabas testudineus, Amblypharyngodon mola, Puntius sophore, Tenualosa ilisha which could provide wholesome nutrition to consumers (Mohanty et. al, 2019).

Marine fish contain significant quantity of Omega-3(n-3) fatty acids such as DHA and EPA. These contribute significantly in the functioning of vital organs viz., heart, brain, immune and reproductive systems. (Connor,2000). Their role in ameliorating many diseases, has been reported extensively viz., cardiovascular disease (Nordoy,2001), depression, lupus (Duffy et. al,2004), rheumatoid arthritis (Cleland et.al 2003) psoriasis, crohn’s disease (Tsujikawa et. al,2000), ulcerative colitis (Alex and Triadafilopoulos,1992) asthma (Nagakura et.al,2000), kidney disorders, diabetes and cancers (Larsson et. al,2004).

The development of a more diversified fish processing sector with raw and processed fishery products could be witnessed over the years. There are many references for the development of by-products from fish and their use in feed, fish silage, fertilizer, biofuels, food packaging, human food or nutraceuticals or pharmaceuticals (Arvanitoyannis & Kassaveti, 2008; Govindharaj, Roopavath, & Rath, 2019; Herpandi, Rosma, & Wan Nadiah, 2011; Kim & Mendis, 2006; Yuvaraj et. al, 2016). However, its use in food and nutraceutical fields is still challenging because of safety, stability and bioavailability issues and lack of good market potential.