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Aquaculture stands out as one of the most rapidly expanding sectors in global food production, with various fish species serving as crucial components farmed across diverse regions worldwide. The primary component of fish flesh is water, comprising approximately 70–80% of the fillet’s weight. The water in the muscle of fresh fish is closely bound to the proteins within its structure. Proteins are vital nutrients crucial for growth and as integral components of the body’s cells. Amino acids (AAs) play a significant role as the fundamental building blocks of proteins. The conformational structure, as well as the chemical and biological properties of a protein, are influenced by the type and rank order of its AAs. Therefore, it is important to elucidate the protein content, its requirements, and its significant role in different species of fish. This book chapter elucidates a literature-based survey about the types of protein found, the approximate protein and AA content present in different fish species, and the requirement of AAs in different species of fish, which will be helpful for aquaculture.

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Aquaculture production is becoming more demanding with each passing day to meet the increasing demands for fish protein sources. Around 17% of the animal protein supply worldwide and 7% of all the protein consumed by humans comes from fish, and it is expected that seafood will be considered the future trustworthy food source for the population living below the poverty line. Maintaining the sustainability of aquaculture production is a challenging task because the different challenges faced in aquaculture include feeding efficiency, overfeeding, food wastage, nutrient loss, and disease-free conditions to maintain health, which can be achieved by providing an adequate amount of feed in a completely balanced diet. The variations in dietary requirements arise due to different species, sex, developmental stages of fish, and the environmental conditions in which the fish are living. The important aspect of feed is to meet the nutritional requirements and be easily digestible to promote fish growth. Consumption of feed also depends on taste to prompt fish to consume feed and 32maintain digestibility, because feed ingredients influence the sensory and qualitative characteristics of fish, which in turn meet consumer expectations. Fish protein diets containing essential amino acids (EAAs), amino acid composition, and protein structural configuration are the best choice for feed preparations for optimal growth and reproduction, as well as other physiological processes of fish. Dietary nutrients that are eliminated through feces are included in the undigested components but not in the fish’s nutrition; thus, an important condition of the diet is to provide a high level of digestibility. The energy digestibility coefficient is considered when designing complete feeds.

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In fish farming, nutrition is usually reflected as one of the most critical factors because it is directly related to fish performance and health, as well as total production costs. To avoid reduced or unhealthy growth and high feeding costs, and ultimately lower gross margins, nutritional requirements should be accurately determined for commercially important fish species in different growth stages, considering the end product of farming. 48Proteins are among the essential nutrients and are considered an integral part of fish feed due to their significant role in body maintenance, growth, and health status of fish. According to most of the available literature, total protein requirements have been extensively studied in fish nutrition. First, optimal levels of protein content are usually established in fish feeds to achieve maximum performance of different species of fish. Second, most of the available literature has reported crude protein content, and little attention has been paid to improving the quality of dietary protein (DP). Third, protein requirements are established for feeding fish that are usually marketed as whole fish, while other marketing methods are completely neglected. All these three concerns about protein requirements need to be properly addressed because this important nutrient is composed of amino acids (AAs) that are needed in appropriate proportions, particularly EAAs, for the synthesis of optimal body protein. Its extra amounts and/or unbalanced forms in feed are utilized as an energy source, which may result in high fat deposition or high nitrogen excretion in water. Consequently, the growth and health of fish, as well as the total costs of production, and hence net profits, are adversely affected. In addition, feeding fish with DPs without considering the way the harvested product would be sold could also result in significantly lower net profits. Taking into account all these scenarios, this chapter stresses the establishment of DP requirements through appropriate models by considering multiple factors such as DP quality, energy content, sustainable growth, species with high market demand, growth stage, cost-benefit analysis, and the way the end product is marketed. Comprehending sustainable and ecosystem-supporting fisheries and aquaculture practices is suggested in accordance with the recommendations of the “Food and Agriculture Organization Code of Conduct for Responsible Fisheries” to promote sustainable and healthy fish farming to ensure long-term food security, food safety, and livelihoods of fishermen and consumers.

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Lysine, an indispensable amino acid (AA), is crucial for fish growth, health, and feed efficiency. The shift towards sustainable aquaculture practices and the increasing inclusion of plant-based proteins in diets highlight the importance of lysine supplementation. This chapter provides an synthesized review of lysine’s metabolic roles, emphasizing the need for species-specific lysine requirements to optimize aquafeed formulations and support the productivity of farmed fish. Advances in understanding the molecular impact of lysine on nutrient-sensing pathways have profound implications for improving the utilization of alternative protein sources. The chapter also addresses lysine’s interactions with other AAs, noting the potential for antagonism that can affect metabolic processes. Additionally, it considers the environmental and economic aspects of sourcing highquality lysine for aquafeed, underscoring the need for innovative solutions to meet nutritional demands sustainably. Collectively, the chapter sets a foundation for future research directions, focusing on refining lysine supplementation strategies in line with the evolving landscape of global aquaculture.

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Methionine, an essential amino acid (EAA), is a linchpin in the complex web of metabolic pathways that govern fish nutrition. This chapter of the book delves into the multifaceted nature of methionine, shedding light on its vital functions, dietary requirements, and its profound implications in the context of sustainable aquaculture practices. Methionine is pivotal in protein synthesis, methylation reactions, and numerous other critical processes. This chapter emphasizes the importance of comprehending these roles in the context of maximizing growth and health in farmed fish and reducing environmental impacts. The chapter provides insights into the diverse dietary sources of methionine and explores the intricate interactions that methionine has with other amino acids (AAs). Moreover, the chapter discusses the exciting prospects in methionine research within aquaculture to enhance its efficiency and sustainability and minimize its ecological footprint. Conclusively, this chapter underscores the indispensable role of methionine in fish nutrition, influencing growth, health, and the sustainability of aquaculture practices. It aims to provide valuable insights 120and guidance to researchers, aquaculturists, and nutritionists operating in the dynamic and evolving field of aquaculture.

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With the expansion of aquaculture to ensure global food security over the last few years, research has been able to unveil the functional roles of essential amino acids (EAAs) contained in fishmeal, which is becoming expensive and scarce, in optimizing the effective nutrition of farmed fish species, which has become a major concern for the commercial success of aquaculture. Valine is considered one of the EAAs in fish, and its content in aquaculture feeds depends on the type of ingredients used. Valine is a glucogen, while the synthesis of participating proteins is the most important physiological function of this AA, so it is closely linked to fish growth and plays an important role in regulating growth. It also plays an important role in fish immunity as it acts on intestinal absorption. Several studies have shown that a deficient or excessive level of valine in diets negatively affects the growth performance of fish. Valine cannot be synthesized de novo by fish and other animals and must be obtained by breaking down proteins in the diet, particularly fishmeal. To overcome this problem, dietary supplementation with synthetic L-valine is used as an alternative to reduce dependence on fishmeal in fish diets. Given the importance of valine in animal and fish production, its production has become industrialized through synthesis using microorganisms.

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Appropriate nutrition plays a vital role in increasing fish production through aquaculture. However, this system cannot succeed and sustain without practical feeds that are species-specific, nutritionally balanced, easily affordable, and environmentally friendly. Of all the nutrients needed by fish, protein is one of the most expensive components of fish feed since it is used for tissue growth and repair, as well as providing both essential and non-essential amino acids (EAAs) required to build protein and energy for growth and maintenance. Among all the nutrients, protein is one of the main essential nutrients required by fish for maintaining their life and growth. It is not only essential for growth and maintenance but also important for enzymatic activities and hormone production, which are vital for normal metabolism. Therefore, it is imperative to determine the precise protein requirement of different fish species. Since the quality of protein is actually determined on the basis of amino acid (AA) mixture, it 188is significant to understand the role of individual AAs in the growth of fish. AAs play a vital role in almost all the bodily functions of fish. Among 22 AAs, 10 are considered essential and 12 are considered non-essential in fish. Among EAAs, phenylalanine, in the form of an aromatic AA, is required for protein synthesis and growth promotion in fishes. Fish have different specific phenylalanine requirements based on their species, life stage, size, and habitat. Fish nutritionists and academics studying aquaculture frequently use feeding trials to ascertain the dietary needs for phenylalanine and other important AAs. In these experiments, diets containing different amounts of the tested AAs are prepared, and the fish’s growth performance, feed efficiency, and other pertinent characteristics are monitored. Usually, the ideal dietary phenylalanine needed for a given fish species is stated as a ratio to other necessary AAs or as a percentage of the overall diet. Furthermore, phenylalanine needs in fish can be influenced by water temperature, water quality, and the presence of other nutrients in the diet. It is advised to confer with specialists in fish nutrition and aquaculture, examine scientific literature, or read publications on aquaculture research for precise and species-specific information on the phenylalanine requirements of fish. This chapter reviews the research on the phenylalanine requirement of diverse fish species, which would be helpful in boosting their production.

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Tryptophan is an essential amino acid (EAA) that plays a vital role in the growth, development, and general health of fish. The function and precise requirements in fish nutrition have garnered great interest in recent years. Detailed investigations regarding the understanding of tryptophan requirements in various fish species include the physiological significance of tryptophan and the effects of tryptophan excess or deficiency on fish growth and health conditions. Understanding the specific tryptophan requirements for different fish species is paramount for conceiving tailored nutrition strategies that promote sustainable aquaculture practices. Furthermore, continued research efforts aimed at unraveling the intricate metabolic pathways and physiological functions of tryptophan will contribute to the advancement of fish nutrition and welfare, ultimately fostering the growth and development of the aquaculture industry. The aim of the present chapter is to consolidate the current knowledge related 220to various aspects of tryptophan requirements in fish, which is of great significance in aquaculture and fisheries management.

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The management of fisheries and aquaculture is significantly impacted by the histidine requirements of different fish species. This study delves into the specific histidine necessities of different fish species with the aim of optimizing their growth, health, and overall performance within aquaculture systems. The research has yielded invaluable insights into the diversity of histidine requirements among these species, underscoring the significance of customized nutritional approaches to meet their distinct dietary requirements. Meeting histidine requirements is a fundamental step in promoting the progression of sustainable aquaculture practices, safeguarding the well-being of a variety of fish species, and upholding the production of top-quality seafood to meet the demands of a growing 244global population. Ongoing research in this field holds the potential to further enhance our comprehension and refine the effectiveness and sustainability of fish farming practices.

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Accurate estimates of the maintenance requirement of amino acids (AAs) are important for feed formulation. Branched-chain amino acids (BCAAs) serve not only as substrates for protein synthesis but also play a role in regulating protein synthesis. BCAAs regulate various key signaling pathways. Leucine is believed to be an indispensable AA in most aquatic species because its carbon skeleton cannot be synthesized in vivo. It functions as a major regulator in body composition, growth performance, mTOR activation, and metabolism at multiple levels. Leucine plays a crucial part in investigations, which have consistently emphasized the significance of dietary quantities of BCAAs in the development and growth of fish. Based on the existing 266evidence, it appears that fish need slightly greater quantities of BCAAs throughout the early stages of life compared to later stages. The optimum dietary leucine requirement of fishes can be revealed by various trial data and analysis of feed conversion ratio (FCR), protein efficiency ratio (PER), specific growth rate (SGR), final weight (FW), weight gain rate (WG), leucine retention efficiency, and body protein deposition (BPD). This chapter provides full information on leucine metabolism, the empirical method used for leucine requirements, the dietary leucine requirement of different fish species, natural or synthetic leucine sources, the interaction of leucine with other AAs, the ideal protein concept, important functions in the fish body, nutritional disorder of leucine deficiency, and factors affecting leucine requirement. The optimum dietary leucine requirement has been determined for various fish species, showing a wide range of values ranging from 11.5 to 91.0 g/kg of dietary protein (DP) to date.

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Amino acids (AAs) are essential ingredients in fish nutrition for physiological functions, optimum growth, and development. Arginine is an essential amino acid (EAA) and must be incorporated into the diet. The requirement of arginine ranges from 3% to 8% of dietary protein (DP). Among the various feed components, the arginine level ranges from 1.12% to 11.23% of the DP basis. Arginine has a range of physiological functions, including growth, osmoregulation, immunity, antioxidant effects, and ammonia detoxification. It acts as the precursor for nitric oxide (NO), polyamines, and other important metabolites. Arginine plays a role in insulin and growth hormone stimulation to maintain growth and development. It regulates homeostasis by altering the mechanism that adenosine 5’-monophosphate (AMP) activates to the activated protein kinase (AMPK) pathway, activates the target of rapamycin (TOR) signaling pathway, and hence regulates protein synthesis. The aforementioned functions of the AA arginine have been covered in this chapter to provide a complete understanding of the role of arginine and its necessity in the fish diet for optimal growth.