Peptides are organic molecules formed by the union of two or more amino acids through peptide bonds, which occur between the carboxyl group of one amino acid and the amine group of another. These molecules differ from each other according to the number and type of amino acids that form them. When they are made up of two, three, and four amino acids, they are called a dipeptide, a tripeptide, and a tetrapeptide, respectively, and so on. However, peptides with more than seventy amino acids are called proteins.
In the 1950s, it was discovered that peptides have beneficial health properties. At this time, many peptides had their chemical structures defined, such as insulin and glucagon. Since then, their syntheses, separations and applications have been studied.
Peptides perform many diverse and important functions in the body. Some peptides act as hormones or hormone regulators, others are neuropeptides, neurotransmitters, analgesics and even antibiotics[4,5].
In this context, bioactive peptides are defined as those peptides that deliver different physiological effects or biological functions, such as those mentioned above. According to López-Barrios, Gutiérrez-Uribe and Serna-Saldívar, bioactive peptides are defined as fragments of amino acid sequences in a protein that confers biological functions and nutritional value.
Being molecules of chemical structure smaller than proteins, peptides are absorbed and used directly by the body. This absorption occurs in the intestine and generates some functional properties equivalent to those of proteins.
In animals, these biomolecules present and exert some physiological or regulatory functions or both, crucial for their development. For example, the peptide PEC-6o activates ATPases in the small intestine and other tissues, enzymes that act directly in the production of cellular energy, essential for life.
Besides these, some peptides have an antimicrobial function, responsible for the health of the local microbiota. In the brain, several peptides are released, regulating the endocrine status, food intake and behavior of animals. Therefore, peptides are considered excellent and important supplements to incorporate into animal nutrition, such as those related to aquaculture.
Aquaculture: Definition and Perspectives
According to Embrapa, Empresa Brasileira de Pesquisa Agropecuária (2019), aquaculture can be defined as the science that seeks to study and promote advances in the techniques of farming aquatic animals. Among these animals, we can cite fish, crustaceans (such as lobsters and shrimp), molluscs (squids and octopuses), algae and other organisms created in aquatic environments, such as frogs, turtles and alligators — exotic animals that can be cultivated and consumed as food by humans.
Internationally, the economic impact derived from this practice became known as the Blue Revolution. This denomination makes an analogy to the term Green Revolution — linked to the transformations agriculture went through since the 1950s.
The transformations related to the practice of aquaculture, after this period, still provide a great perspective for the development of a sustainable market for the cultivation of aquatic species, both for controlled and semi-controlled systems.
Since 2016, the production and trade of animals through aquaculture have surpassed fishing and, since then, aquaculture has been responsible for half of the fish production in the world. Since the year 1980, when fish production through fishing suffered stagnation, production has maintained in the range of 90 million tons per year. In 1989, the yearly production through aquaculture increased to 16.5 million tons, and in 2015 to 106 million tons per year.
With a perspective of constant growth in the aquaculture market, there is a demand for continuous improvement in managing this culture. Thus, it is of great importance to understand the nutritional needs of each species, seeking adequate food for the ideal development of animals.
However, some foods used to feed these species may not meet all their requirements, as they may not be very attractive for animals or be of low digestibility to the organism.
As previously mentioned, bioactive peptides offer high absorption to the body, along with also providing several biological and functional properties. Therefore, they are considered interesting supplements to add to feeds oriented for aquatic animals.
Employment of Bioactive Peptides in Aquaculture
The use and development of an adequate supplementation for each species of aquatic animals requires previous studies in order to understand the individual dietary needs, especially when it comes to proteins.
The investment in an adequate diet will provide better health for these animals, as well as a higher survival rate, thus contributing to their growth and performance. In this way, a good quality product is delivered to the consumer market, along with a consequential financial return to cultivators.
The species Oreochromis niloticus, popularly known as Nile Tilapia, is an aquatic animal of easy culture, being raised in several regions of the world, especially in tropical and subtropical climates. However, the nutrition of these species, in which the protein fraction of the feed is considered the main ingredient for growth and nutrition[14,15], presents a high cost of operation, reaching up to 70% of the total spent on the breeding practice[16,17]. One of the main obstacles new alternatives face is the low acceptability by the animals. As a parameter of acceptance or rejection (or both) of consumption, palatability is used, and it aims to find out whether or not the species in question has eaten the food. Therefore, palatability becomes a determining factor for the success or failure of these alternative sources, making it necessary to search for a nutritionally rich food that is at the same time accepted by the species.
Brazil is a country that globally stands out in the market of poultry and swine production, as it has these processes widely established. As by-products of these production chains, viscera, feathers and offal can be mentioned. As a way of using these products and consequently reducing production costs, they can be utilized after processing and commercialized in the form of protein hydrolysates.
According to Peixe BR (2020), Nile Tilapia species were submitted to a diet based on Chicken Protein Hydrolysate, a product developed by BRF Ingredients. This protein has bioactive peptides, smaller amino acid chains, and is produced through enzymatic hydrolysis.
The Hydrolyzed Chicken Protein (PHF) from BRF Ingredients is formulated with the objective of improving the performance and health of the animals. It is produced through an enzymatic hydrolysis process that generates smaller chains of amino acids, the so-called bioactive peptides. These peptides may have specific biological activities such as antimicrobial, antioxidant, antihypertensive, and immunomodulatory activities.Besides the fact that 100% of the peptides had a molecular mass below 3,000Da, in a peptidomic analysis, 78 peptides were identified with functionalities such as anti-amine, antioxidant, immunostimulant, angiotensin inhibitor (ACE), stomach membrane regulator, and others.
Based on the existence of these peptides in CPH, it was possible to observe results of improved blood pressure in cats, increased survival rate in shrimp, and better yield in tilapia fillets, when the ingredient was included in the formulations.
With the continuous growth in the aquaculture market, the need and search for knowledge about the appropriate diet for the rearing of each species is perceived. Due to the promotion and growth of this market, there is a need to seek alternative sources of hydrolyzed proteins, that provide nutrients and also the differential of the presence of bioactive peptides to the animals, since they are more easily absorbed by the body and have additional functionalities due to the presence of bioactive peptides that help in animal performance and health.
Bioactive peptides present themselves in this market as important nutrients for the development of feeds for aquatic animals and are essential for the reproduction, growth and development of aquatic species.
From what research concludes, Chicken Protein Hydrolysate, obtained through enzymatic hydrolysis, has the appropriate nutritional requirements and acts in specific functionalities, favoring animal health and performance (due to the presence of bioactive peptides) while also having a high acceptance by the fish.
 WU, G. Amino acids: biochemistry and nutrition. Boca Raton: CRC Press; 2013.
 GUTTE, B. Peptides: Synthesis, Structure, and Applications. Academic Press: New York, 1995.
 ACHADO, A.; LIRIA, C. W.; PROTI, P. B.; REMUZGO, C.; MIRANDA, M. T. M. Sínteses química e enzimática de peptídeos: princípios básicos e aplicações. Química Nova, 27, 2004.
IRANDA, M. T. M. Tese de Livre Docência. Universidade de São Paulo, Brasil, 2000.
 DIAS, G. M. P. Avaliação do perfil dos peptídeos bioativos do queijo coalho fresco produzidos no município de Cachoeirinha – PE. 2010. 53fls. Dissertação (Mestrado em Ciências Biológicas) - Universidade Federal de Pernambuco, Recife. 2010.
 LÓPEZ-BARRIOS L.; GUTIÉRREZ-URIBE, J. A.; SERNA-SALDÍVAR, S. O. Bioactive peptides and hydrolysates from pulses and their potential use as functional ingredients. J Food Sci. 2014.
 SCOTT, G. F. Biologia do desenvolvimento. 5ª ed., FUNPEC Editora, 2003.
 LI-CHAN, E. C. Y. Bioactive peptides and protein hydrolysates: research trends and challenges for application as nutraceuticals and functional food ingredients. Curr Opin Food Sci. 28–37, 2015.
 KAIRANE, C.; ZILMER, M.; MUTT, V.; SILLARD, R. Activation of Na, K-ATPase by an endogenous peptide, PEC-60. FEBS Lett.1–4 1994.
 ALVES, D. S. Atrato-palatabilidade para juvenis de Tilápia do Nilo (Oreochromis niloticus). Universidade Estadual do Oeste do Paraná. Programa de Pós-Graduação em Recursos Pesqueiros e Engenharia da Pesca. Tese de doutorado, 83f., 2019.
 BEVINS, C. L.; SALZMAN, N. H. Paneth cells, antimicrobial peptides and maintenance of intestinal homeostasis. Nature Rev Microbiol. 9, 356–368, 2011.
 ENGEL, J. A.; JERLHAG, E. Role of appetite-regulating peptides in the pathophysiology of addiction: implications for pharmacotherapy. CNS Drugs, 28, 875–886, 2014.
 SIQUEIRA, T. W. Aquicultura: a nova fronteira para produção de alimentos de forma sustentável. R. BNDES, Rio de Janeiro, v. 25, n. 49, p. 119-170, jun. 2018.
BRITO, J.M.; PONTES, T.C.; TSUJII, K.M.; ARAÚJO, F.E.; RICTHER, B.L. Automação na tilapicultura: revisão de literatura, desempenho, piscicultura, tecnologias, tilápias. Nutritime, v.14, p. 5053-5062, 2017.
 National Research Council (NRC). Nutrient requirements of fish and shrimp. National Academies Press, Washington, 379p., 2011.
SILVA, T.C.; ROCHA, J. D. M.; MOREIRA, P.; SIGNOR, A.; BOSCOLO, W. R. Fish protein hydrolysate in diets for Nile tilapia post-larvae. Pesq. Agropec. Bras. 52(7): 485-492, 2017.
 CRIVELENTI, L. Z.; BORIN, S. A. PIRTOUSCHEG, J.E.G. NEVES & E.M. ABDÃO. Desempenho econômico da criação de tilápias do Nilo Oreochromis niloticus em sistema de produção intensiva. Veter. Notic., 2(12): 117-122, 2006.
 FURUYA, W. M. Tabelas Brasileiras para a Nutrição de Tilápias. 1ª ed. Toledo: GFM. 100p., 2010.
 FRIES, E.M., J.D. LUCHESI, J.M. COSTA, C. RESSEL, A.A. SIGNOR, W.R. BOSCOLO & A. FEIDEN. Hidrolisados cárneos proteicos em rações para alevinos de Kinguio Carassius auratus. Bol. Instit. Pes., 37(4): 401-407, 2011.
 MERINO, G.; BARANGE, M.; MULLON, C. Climate variability and change scenarios for a marine commodity: modelling small pelagic fish, fisheries and fishmeal in a globalized market. J. Mar. Syst., 81(1): 196-205, 2010.
 KOTZAMANIS, Y. P.; GISBERT, E.; GATESOUPE, F. F.; INFANTE, J. Z.; CAHU, C. Effects of different dietary levels of fish protein hydrolysates on growth, digestive enzymes, gut microbiota, and resistance to Vibrio anguillarum in European sea bass Dicentrarchus labrax larvae. Comp. Biochem. Physiol. Part A, 147(1): 205-214, 2007.
 OVISSIPOUR, M.; KENARI, A.A.; NAZARI, R.; MOTAMEDZADEGAN, A.; RASCO, B. Tuna viscera protein hydrolysate: nutritive and disease resistance properties for Persian sturgeon Acipenser persicus L. larvae. Aquaculture Research, v.45, p.591-601, 2014.
 SRICHANUN, M.; TANTIKITI, C.; KORTNER, T.M.; KROGDAHN, A.; CHOTIKACHINDA, R. Effects of different protein hydrolysate products and levels on growth, survival rate and digestive capacity in Asian seabass Lates calcarifer Bloch larvae. Aquaculture, v.428-429, p.195-202, 2014.
 CAHU, C.L.; ZAMBONINO INFANTE, J.L.; QUAZUGUEL, P.; GALL, M. M. L. Protein hydrolysate vs. fish meal in compound diets for 10-day old sea bass Dicentrarchus labrax larvae. Aquaculture, Amsterdam, 171: 109-119, 1999.
 HEVRØY, E.M.; ESPE, M.; WAAGBØ, R.; SANDNES, K.; RUUD, M.; HEMRE, G.-I. Nutrient utilization in Atlantic salmon (Salmosalar L.) fed increased levels of fish protein hydrolysate during a period of fast growth. Aquaculture Nutrition, Oxford, 11(4): 301-313, 2005.