Commercial fishing and aquaculture usually generate large amounts of waste that must be disposed. This include trash fish – a term widely used for those fish which are not used for direct human consumption, which may be either landed and discarded at the sea itself or low value fish used for human consumption. In a country such as India where marine fishery is of multispecies composition, the occurrence of by-catch consisting of several species of fish is quite common and a study that estimated the quantity of by-catch discarded by the trawlers operating along Indian coasts had been significantly huge. In addition, seafood processing activities have raised serious waste production and disposal concerns all across the globe. Most of the objections to off-shore dumping of wastes were based on odour problems, floating debris and visible surface slick, attraction of undesirable predator species, increased turbidity and dissolved oxygen depression of bodies of water. The authors discuss about the common practice of disposing residue of the seafood industry by coastal states into natural open bodies of water, landfills, which are dumped aside as heaps in nearby harbours and seafood processing units which raises environmental concerns and the solutions that could be applied for their effective utilization in a circular economy.
The consumption of fish products owing to its nutritional properties has been progressively increasing around the world, as it is one of the most dependable sources of vital nutrients to promote good health. Fish food is an important nutrient source in various parts of the world to meet the dietary requirement of essential nutrients such as amino acids, fatty acids and minerals, etc. Fish production contributes a major source of income for specific population groups and aquaculture is considered to be a growing industry that has been supporting their livelihood in many developing countries. In Asia, Africa and America, fish food also plays an essential role in the socio-economic growth of rural and urban communities. As per the report of FAO (2016), around 78% of the seafood products are being supplied to International Markets.
Seafood is an important source of nutrition among people in different parts of the world. The presence of multiple nutritional value in seafood, especially in fish such as high-quality proteins, essential amino acids, n-3 polyunsaturated fatty acids (PUFA), vitamin D, iodine, trace elements and minerals attracts consumers to promote a healthy lifestyle. Numerous research findings have disclosed the positive health promoting benefits of consuming fish in diet, especially among adults. The bioactive constituents such as n-3 PUFAs, protein, fibre, taurine, sterol and pigments present in the sea food supports various biological functions such as the growth of the human brain and nervous system. Therefore, fish is considered as a functional food and consumption of the same can help in alleviating food crisis in many developing countries and to ensure dietary availability of essential nutrients. Hence, large-scale production of wide variety of edible fish species is rapidly increasing in developed countries for maintaining a healthy life.
Between 1954 and 2014, net fisheries and aquaculture productivity increased by more than eightfold, owing to advances in fishing technology and significant developments in aquaculture. In 2016, the total fisheries production was about 171 million tonnes (MT), in which about 151.2 MT was estimated as essentially being made available for human food supply. As per the reports of FAO, 2020, the Global Seafood Production was about 178.5 million tons (MT) in the year 2018. Further, it has been reported that progressive growth in the human consumption of fishery products will reach upto 204 MT by the year 2030. (Venugopal., 2021)
Fish/Seafood Processing Industry is one of most important industries in the world. The increased consumption of sea food products, owing to the fact that they offer multi-nutritional benefits has led to larger production of global seafood and this is only expected to increase in the future. Most importantly, aquaculture sector has been rapidly growing across the world and it has been supporting the livelihood of millions of people engaged in fishing related activities. Further, with the production of a variety of seafood there is a major impact in the socio-economic development of rural and urban populations of several developing countries. It has been estimated that 15% of the animal protein requirement comes from fisheries products alone and this accounts for 4-5 % of the calculated minimum requirements for protein.
Among the fish producing countries, India ranks second in the world, which accounts for an estimated 7.56% of the global fish production. Fisheries sector has been demonstrating stupendous growth with record fish production that comprised of approximately 245 lakh tons in the financial year 2020-21. The revenues generated by the fisheries sector from export of their various products was INR 46,663 crores during 2019-20.
India’s fisheries production are majorly sourced from both inland and marine resources, as it has a long coastline stretching almost two-thirds of the country (about 8129 km) with economic zones of approx. 2 million square kilometres and huge reservoirs offering surplus production of fish and fishery products. India is a major exporter of over 50 different types of fish and shellfish products to 75 different countries around the world and has exported seafood worth USD 5.96 billion (EUR 4.9 billion) during the financial year 2020-21. The marine products export from India is targeted to reach USD 14 billion by 2025.
Generation of Fish Processing Waste
Fish processing activities involves sequence of processing steps from the time of harvest up to the time of delivering the final marketable product ready for supply. Fish processing firms located in developing countries experience more losses or wastage during different stages such as loading and unloading, processing, storage, transportation and marketing, due to technical, financial, infrastructural and managerial constraints. The generation of wastes due to spoilage and quality downgrading of the product is influenced by several factors, such as high ambient temperatures, lack of access to services, infrastructure, basic technology, a reliance on more traditional smoking and drying techniques for preservation and lack of cooling (cold chain) facilities. This results in substantial loss in the form of waste from the period of harvest and during the stages of processing.
The generation of waste from the entire fisheries sector accounts for 35% of global catches where 9-15% of these losses arise from by-catch. The amount of production lost (spoilage or thrown away) after landing and prior to consumption was estimated to be 46.17 metric tons. The generation of fisheries waste during post-harvest fish losses (PHFL) comprises the fish distribution chain: harvesting, transporting, marketing, processing, packaging till consuming that finally ends up with waste of about 27%. The wastes generated during the PHFL are mainly attributed to enzymatic, oxidative and microbiological spoilage. There is an estimation of postharvest losses in fisheries in developing countries to be up to 50 % of their domestic fish production (FAO, 2016).
The FAO fisheries glossary outlined that the proportion of the total organic material obtained through catch, which are discarded or dumped into sea contains postharvest wastes such as offal containing a mixed composition of dead or alive. Production of fish waste (%) in major coastal cities of India (Ahmad and Bhuimbar, 2019) shows that among the coastal regions, high level of fish waste is generated in Mumbai (23%) followed by Chennai (15%); Mangalore (14%) and Kochi (12%) respectively. The waste generated in India during various fish processing showed significant difference in the percentage of waste produced for fish fillets (70%); fish steaks (30%); whole and gutted fish (10%). The non-edible parts generated from the processing is defined in various synonyms such as fish waste; by-product; co-product; fish offal, fish visceral mass; fish discards (Suresh and Prabhu, 2012) or rest raw materials or secondary raw materials. The processing residues contains a mixture of solid waste, such as whole fish waste, fish head, viscera, tails, skin, bones, blood, liver, gonads, guts, belly flap trimmings and liquid waste effluent or stickwater.
Composition of fish waste
The organic by-products which consist of the inedible fractions are the most abundant segments that constitute the solid waste. Most of the fish solid waste is produced from different levels such as fish capturing at sea, aquaculture activity, fish processing firms and fish markets having retail trade and restaurants. This comprises of discards from processing of both aquaculture and wild capture.
Apart from processing waste, trash fish are another segment of discards that constitutes significant proportion of marine solid waste. Most commonly, trash fish is comprised of juveniles of commercial species of small benthic and mesopelagic fish, etc. below the minimum landing size which has less or no economic value. The wastewater or effluent released from processing is characterized by the presence of high concentration of organic matter such as fats, oils and grease, excess nutrients (nitrogen and phosphorus); proteins and salts. Particularly, protein remains present in the effluent comprises of myofibrillar proteins, collagen, gelatin, enzymes, soluble peptides and volatile amines. Also, the effluent is characterized by high salinity, due to frequent application of sodium chloride to exude slime, blood and other particles for improving cleaning efficiency and water removal.
Effect of fish waste on aquatic environment
Improper fish waste disposal poses the threat of a negative environmental impact from the release of organic materials into aquatic ecosystems. The decomposition of the wastes is influenced by autolysis, bacterial degradation and lipid oxidation. During degradation of the fish waste, emission of offensive odour along with leakage of body fluids imposes serious ill-effects to the environment. Primarily, the degradation process is initiated by membrane-bound enzymes leading to autolysis of the decaying waste. Further, the degradation is carried out by rapid growth of bacteria existing on the outer surface of fish entrails (skin, gills and intestines). Various bacterial communities such as Aeromonas spp., Enterobacteriaceae; Shewanella putrefaciens and Psychrotolerant are involved in the microbial reduction of trimethylamine oxide (TMAO) (osmoregulant) present on the decaying tissues, leading to production of ammonia-like fishy odour. Further, the microbial metabolism also leads to the release of various biogenic amines: putrescine, histamine and cadaverine, organic acids, sulphides, alcohols, aldehydes and ketones responsible for offensive odour.
Oxidation of lipids: Polyunsaturated acylglycerol present in tissues is a free radical process catalyzed by light, heat and enzymes, etc. This produces glycerol with numerous oxidative products such as alcohols, aldehydes, ketones, hydrocarbons, volatile organic acids and epoxy compounds responsible for malodour and rancidity.
Fish waste disposal methods and issues
Fish waste is costly to dispose, due to its high organic content. Most of the processed solid fish waste is disposed in rigid manner, such as (i) disposal or dumping in water bodies; (ii) land filling and (iii) incineration methods that are discussed below.
One of the most traditional practices of discarding fish waste is simply dumping huge quantities of residues into water bodies such as sea and ocean which adversely affect the marine environmental health. Ocean dumping related activities causes multiple pollution issues such as lower oxygen levels at ocean bottom, burial or stifling of aquatic organisms and spreading pathogenic infections from putrefying organic matter (Venugopal, V., 2021).
Direct disposal to land is also widely practiced all over the work. This kind of improper disposal of fish waste rich in protein and lipids to lands has serious environmental impacts such as release of bad odour. Beside, proteolytic and other hydrolytic enzymatic activity occurring in tissues of viscera and muscles will rapidly degrade the protein-rich wastes with release of volatile ammonia and high ammonia concentration facilitating the microorganisms to produce nitrates. Hayes et al., 1993 has reported that calcium from the fish bones cause ammonia gas resulting in an alkaline medium unsuitable for acidic soils.
Fish waste is categorized as a certified waste to dispose at landfill due to its high organic load. The cost requirement for landfill dumping can go up to US$150 per ton (Knuckey et al, 2004). Most commonly, this kind of disposal involves aerobic composting that transforms the organic matter into valuable bioproduct rich in humus.
To overcome the impact of toxic gases, well-designed landfill operations are of utmost importance in order to minimize its impact. Further, landfill method of disposal contributes significantly to emission of greenhouse gases (GHG). A recent study on fish waste disposal by landfill in Port of Vigo, Spain has observed that decomposition of fish wastes of about 9120 tons under anaerobic condition resulted in emission of gases provided in Table 3.4. The same study has reported that the environmental impact of the landfill assessed by ecological footprint (measuring and communicating human induced environmental impacts) method in which air emissions were depicted as main contributors to the EF value was calculated to be 0.15 ha/ton.
Incineration is an approved method of waste utilization which involves combustion of the fish waste in a special combustion unit with fuel addition to achieve the appropriate temperature. This practice finally produces ash which could be landfilled. During this process, heat is retrieved indirectly through heat transfer into hot water or steam. This approach is not economically viable, as high cost is involved for setting up incinerator to treat fish waste typically having high moisture, low energy content and excess chloride which affects the process. (Archer et al., 2005)
Minimizing fish waste disposal through developing valuable products
Since fish solid waste is produced in large quantities by the fish processing units and urban markets, it is difficult to handle them for reutilization purpose and is commonly disposed along with other municipal solid waste. It is quite common that high levels of municipal solid waste are disposed by landfill in developing countries: India (90%);Sri Lanka (85%); China (50%) and Thailand (65%) (Ojha et al., 2012).
Most of the landfills located in dump sites face challenges related to toxic gas emission, water and soil contamination (Visvanathan et al., 2005). Fish waste has certain distinct characteristics such as high moisture content, microbial load, endogenous enzyme that provokes rapid degradation of organic matter (Villamil et al., 2017). Due to such characteristics, land filling and incineration are regarded as ineffective ways of disposing them. The environmental impact level of fish processing waste is depicted in Figure 3.10 showing the risk and possibilities of reutilization towards effective marine bio waste management.
With the demand for seafood increasing rapidly, implementation of cleaner production methods that ensure proper environmental management systems is needed to mitigate the hazards imposed by seafood processing activities. From recycling perspective, dumping of these byproducts in water bodies and landfills not only affects environment, but also leads to loss of bioactive materials which could be transformed into numerous value products for effective waste management. Hence, solid waste and effluents from processing is one of the most important issue from both economic and the environmental point of view in fisheries (Catchpole et al., 2010). It is of utmost necessity to address the issue of such disposal, in order to minimize the ecological impacts of fishery (Bellido et al., 2011). The wastes are an excellent source of protein, lipids and minerals with high biological value (Kacem et. al., 2011) that could facilitate the adoption of new technologies to recover useful products from fish waste.
Conventionally, the wastes are being used for preparation of non-food products such as fish meal, fish sauce, animal feed, etc. (Abdul-Hamid et al. 2002). Most commonly, fish silage is produced, which involves treating the fish solid wastes with organic or inorganic (mineral) acids. However, nutritive loss such as degradation of amino acid (tryptophan); high cost and less silage productivity of organic acids are certain limitations being reported (Arruda et al., 2007). Development in industrial biotechnology processes have led to the exploration of possibilities of utilizing by products of finfish processing to deliver various high value-added products such as fatty acids, peptides, oligosaccharides, enzymes (Ross & Stanton 2011); collagen and gelatin (biopolymers); calcium, vitamins and minerals (micronutrients); flavour and functional ingredients, etc. (Suresh and Prabhu., 2012). Fish oil derived from processing waste is used for the production of renewable energy such as biodiesel (Dave et al., 2014) and biogas (Mshandete et al., 2004).
Numerous technical approaches such as physical, chemical and biological are being adopted for effective management of the wastewater, which are characterized by presence of heavy load of organic matter (Palenzuela-Rollon et al., 2002). However, the high cost and energy consumption of physical and chemical treatments and chance of secondary pollution limits their practical efficiency. Anaerobic digestion involves utility of sophisticated instruments, post-treatment, increased maintenance, odour problems, etc. (Montero et al., 2008). Designing anaerobic digestion system for fish waste material is economically unviable and the intrinsic high nitrogen levels present in the waste leads to excessive generation of ammonia that inhibits the digestion process.
Further, de-watering of oily sludge is difficult and requires expensive disposal to landfills (Ward and Slater, 2002). Although, anaerobic digestion is advantageous in terms of producing biogas apart from having low energy requirements, poor operational stability restricts its wide spread usage for treating the effluents. (Shanmugam and Horan, 2009)
Fish waste as a sustainable nitrogenous organic fertilizer for plant growth
Apart from recovery of high value byproducts from fish solid waste, other feasible approaches to utilizing fish waste is in developing organic fertilizers. Fish waste is rich in nitrogen and could be used as a valuable plant fertilizer. Plants requires various macro nutrients such as nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), sulphur (S) and micronutrients such as zinc (Zn), copper (Cu) and manganese (Mn) for their growth.
Fish processing waste is a potentially valuable source of protein, fat and numerous minerals such as Ca, P, K, Na, Mg, Fe, Zn, Mn and Cu and amino acid in a well-balanced proportion. Additionally, they contain other macronutrients such as potassium, magnesium and sulphur. The concentration of nutrients in the waste varies greatly among each species, their size and particularly among the waste segments. Particularly, the level of important macronutrients such as nitrogen, phosphorus and potassium differ among different fish species.
Studies have identified variation in the nutrient levels such as frames and gills of Tuna fish containing high levels of calcium as compared to trimming fractions; high levels of phosphorus in gill waste of Tuna than frames; head waste of Cod fish are reported to comparatively contain a higher concentration of calcium and phosphorus. Based on these study reports, it is highlighted that fish processing waste is a good source of essential bioactive agents to support plant growth with potential of being used as an organic fertilizer.
In summary, developing alternative viable and cost effective eco-friendly procedures is of utmost importance, in order to prevent the environmental pollution caused due to dumping fish processing waste into water bodies and landfills. Most importantly, biotransformation methods could be developed for effective conversion of this nutrient rich waste into beneficial organic products, especially for promoting their sustainable applicability in organic farming.
About the Authors:
1. Radhika Rajasree S.R.
Department of Fish Processing Technology
Kerala University of Fisheries and Ocean Studies (KUFOS),
Kochi – 682506, Kerala.
Email ID: email@example.com
2. L. Aranganathan
Centre for Ocean Research
Sathyabama Institute of Science and Technology,
Rajiv Gandhi Salai, Chennai – 600119.
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