Broodstock nutrition is the most essential constituent of sustainable aquaculture production. Its impact on the reproductive performance and profitability of commercial aquaculture has been the subject of considerable research. The present paper reviews the literature available on the subject, examining the implication of Nile tilapia broodstock nutrition on parameters including maturation, fecundity, fertilization, embryo development, larval quality, and survival rate. The provision of a nutritive diet composed of essential macro and micronutrients including proteins, lipids, carbohydrates, vitamins, minerals, and functional additives, such as prebiotics, enzymes, hormones, and probiotics, in different proportions is discussed. Special emphasis is given to literature dealing with the effects of dietary protein and lipid on vitellogenesis and ovarian maturation, fecundity, egg hatching rate, larval quality, and fry survival number. The impact of the feeding regime on reproductive performance is described.
1 Introduction
Nile tilapia (Oreochromis niloticus) is one of the most commercially important fish species native to tropical and subtropical water bodies in the eastern and western parts of Africa, such as the Nile and Niger River basins and Lakes Tanganyika, Albert, Edward, and Kivu. This species is also found outside of its native range in many parts of the world. Its suitability to different culture techniques; its broad ecological tolerance to various environmental and physicochemical water quality parameters such as fluctuations in pH and salinity, low dissolved oxygen, and high concentrations of chemical nutrients; and its ability to reproduce in captivity make this species one of the most widely cultivated fish around the globe. For this reason, the commercial importance of Nile tilapia is undeniable, especially in the top tilapia-producing Asian and African countries where the demand for tilapia larvae and juveniles is increasing exponentially . To ensure the sustainable growth and expansion of tilapia farming all over the world, prolific measures such as improved nutrition, feeding, and management, with particular emphasis on broodstock, are essential to providing large and high-quality eggs. Providing a balanced diet for broodstock fish is essential not only for the maximum growth and health of juveniles but also to ensure the prime condition of the broodstock fish.
Proper dietary composition is fundamental to broodstock nourishment, as there is a wealth of evidence on nutrient quality affecting health and both quality and quantity of the supply of offspring. Nutrition, which is highly determined by diet, has direct and indirect effects on fish maturation, fecundity, semen quality and quantity, fertilization, embryo development, larval quality, and larval survival. Despite the importance of broodstock fish nutrition, the nutritional requirements of broodstock fish have become poorly understood and less researched due to both the lack of suitable culture facilities that maintain large groups of adult fishes and to the increased costs of extended broodstock feeding investigation. To date, the nutritional requirements of tilapia broodstock have been summarized in previous reports as key factors in tilapia production strategies. Since then, research has expanded to consider specific dietary needs associated with the improvement of tilapia reproductive performance. However, these results are not presented in an organized manner. Therefore, this review aimed to gather information about broodstock nutrition in Nile tilapia and its implications on reproductive efficiency.
2 Methodologies
A recent innovative PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analysis), is a standard that brings together a set of evidence-based practice tools intended to help authors of scientific articles scan a large number of sources when conducting systematic literature reviews or meta-analyses ,checklist approach was used to conceptualize findings, synthesize concepts, and include and exclude articles (Salameh et al., 2020). The literature search for this review was performed using a number of scientific databases, including ScienceDirect, ResearchGate, Google Scholar, Web of Science, SciELO, LibGen, PubMed, Science-Hub, Internet archives, Scopus, CrossRef, and EcoPapers, among others. The searched scientific articles had been published over the previous 30 years.
3 Relevance of broodstock nutrition
Proper dietary composition is fundamental to broodstock nourishment and to a sustainable aquaculture system. There is a wealth of evidence on nutrient quality being able to considerably affect the reproductive performance in fish. Therefore, for many cultured species, broodstock nutrition coupled with the availability of optimal diet is the most limiting factor in determining the variability and unpredictability of reproductive performance. Apart from improved egg and sperm quality, good broodstock nutrition results in the mass production of juveniles and the enhanced growth of fish in order to reach a large size. Despite speciesspecific variations in fecundity, many large-sized fish species tend to produce more eggs, resulting in larger larvae with enhanced survival benefits. Similarly, the quality and the quantity of broodstock nutrition affect the survival of the young. In some fish species, certain essential dietary nutrients, e.g., proteins, lipids, vitamins, and other inorganic compounds, highly determine the fecundity and gonad development aspect of broodstock nutrition.
Sustainable commercial production of tilapia is ensured by the continuous year-round supply of high-quality fish eggs. For this reason, broodstock tilapia could produce good quality fertile eggs with maximum growth and survival rates if they are supplied with formulated, nutritive diets composed of essential nutrients. Nile tilapia are also known to reach sexual maturity at a relatively small size. Furthermore, studies have shown that providing broodstock tilapia with a nutritive diet composed of essential nutrients not only reduced age at first maturity, but also improved vitellogenesis, enhancing the egg quality and progeny development.
Although it is evident that broodstock nutrition has a significant impact on the breeding performance of males, females, and juveniles, there is little information regarding the optimal dietary requirement of many farmed broodstock fish species like the Nile tilapia. This might be due to the short history of commercial intensive aquaculture system, the lack of information on the demand of species-specific broodstock diet, technological dependence, and the financial limitations in conducting these studies. Recently, broodstock nutrition research in aquaculture has been given great attention due to the formulation of quality feed and the use of genetically selected stocks that would improve the profitability of commercial aquaculture. Therefore, the production of an adequate amount of quality seeds with the formulation of appropriate nutritive broodstock diets can highly enhance the reproductive potential, such as a short generation time, high fecundity, and low mortality of fishes, making the industry profitable.
3.1 Nutritional requirements of Nile tilapia broodstock
The provision of a formulated and balanced nutritive diet composed of proteins, lipids, carbohydrates, vitamins, and minerals, along with ration size and feed frequency, to broodstock tilapia that is low cost and environment-friendly would result in optimum growth and improved reproduction.
3.2 Proteins
Protein is an indispensable dietary ingredient in broodstock tilapia feed that provides essential and nonessential amino acids and is used to offer highly available energy when other energy sources are inadequate and for the synthesis of new tissues, hormones, enzymes, and antibodies. Proteins are used as a source of energy for the reproductive process, including the aggressive behavior of the males, for mating, territory defense, and in oral egg incubation. Hence, the inclusion of optimum dietary protein in broodstock nutrition would be fundamental in the formulation of fish feed to avoid poor reproductive performance, stunted growth, and weight loss. Numerous research findings have shown that the breeding results on larval quality and progeny obtained by protein nourishment are better than those by other purified macronutrients. Similarly, the dietary protein level and the feeding regime of female tilapia highly influence oocyte growth, puberty, spawning performance, and egg quality. Subsequently, the quality and performance of larvae will be exceedingly dependent only on the stored nutrients in the yolk.
The provision of an optimum level of dietary protein to broodstock tilapia would improve the growth, development, health, and maintenance of the species, with a knock-on effect on improved reproduction. However, there are great variations in the quality and quantity of the protein requirement of broodstock tilapia. For example, the water temperature, salinity, age, sex, amino acid composition, maturation, spawning period, feeding frequency, and dietary energy level are major determinants of the protein requirement. Hence, in broodstock tilapia, the optimal amount of dietary protein is the lowest level of protein that results in the best performance under certain circumstances. Thus, quantification of the total dietary protein requirement of broodstock fish is essential for sustainable and profitable aquaculture since the cost of dietary protein is the most expensive component of culture systems, accounting for approximately 50% of the feed costs. Apart from the dietary protein level, the source of protein (i.e., animal, plant, or both) also vastly determines growth, survival, and other outputs.
The contribution of broodstock protein toward improved reproduction could be ascribed to the strong association of body size growth with prior maturation of gonads, as many investigations have reported on the earlier development of eggs in large-sized broodstock species. Thus, for egg development, fishes might use protein from their body reserve, as indicated by the highest amount of protein in the egg being observed from fishes supplied with 40% dietary protein, which conferred an increased amount of dietary protein and led to the increased amount of protein in the egg. it was recommended that using diets containing 44% of crude protein for Nile tilapia brood fish is adequate.
3.3 Amino acids
A well-balanced broodstock fish diet composed of essential amino acids is crucial for enhancing reproduction and for the normal growth of tilapia: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Deficiency in any of these amino acids can limit protein synthesis, growth, and metabolic activity, leading to reduced weight and reproductive potential. Furthermore, some amino acids, e.g., arginine and glutamate, are essential in the regulation of hepatic glucose and lipid metabolism. Other amino acids including glutamate, glycine, and tyrosine are also involved in the release of pituitary hormones that regulate food intake and the reproductive behavior of fish.
By including the essential amino acids in the broodstock diet in optimal amounts, tilapia farmers can promote the optimal growth, reproductive performance, and overall health of their fish. Furuya et al. (2023) elucidated three levels of CP (i.e., 350, 380, and 400 g kg−1 of the diet) that corresponded to different broodstock.
3.4 Lipids
Dietary lipids are a major source of essential fatty acids and highly digestible energy required by fish to attain optimal growth and development, improved reproductive performance, and health maintenance. Broodstock diets supplemented with oils and fatty acids that are rich in n-3 and n-6 improved the feed flavor, texture, and cell membrane permeability. Moreover, fatty acids play a significant role in the absorption of fatsoluble nutrients such as sterols and vitamins A, D, E, and K. For many freshwater species like the Nile tilapia, the provision of dietary lipids, particularly essential fatty acids, is crucial for numerous physiological functions related to growth and reproduction as they cannot be synthesized in the body.
Although there are variations in requirements due to species, sex, age, breeding stage, and other physiological conditions, the levels of dietary lipids significantly influence reproductive performance, such as the induction of secondary vitellogenesis and ovarian maturation, fecundity, the rate of egg hatching, the quality of larva, and the number of fry survival of many species, including tilapia . Numerous studies elucidated that a lipid level of 10%–20% in fish broodstock diet results in optimal growth without any accumulation of excess fatty tissue. Conversely, the provision of excess dietary lipids to broodstock fish would lead to the excess deposition of fat in the body cavity, which may adversely affect the growth, reproductive performance, value, and storage of processed products and, ultimately, the profitability of the culture system. Limiting the fatty acids in the diet of tilapia broodstock can have a significant impact on their reproductive performance. Several studies have demonstrated that the incorporation of specific lipid sources into the broodstock diet can enhance reproductive outcomes.
3.5 Carbohydrates
Carbohydrates are abundant but nonessential components in the broodstock diet that provide inexpensive energy to spare lipids and proteins for growth and reproduction. Due to its herbivore–omnivore feeding habit, broodstock tilapia has a greater chance of taking more plant materials exposed to higher carbohydrate contents. This species is capable of utilizing dietary carbohydrates as the primary energy source and responds with poor fecundity and spawning efficiency. This might be due to the low nutritional value of the diet for improving reproduction. Carbohydrates in the broodstock diet are used as a major source of energy for courtship, territorial defense, reproduction, mouth brooding, nest building, and osmoregulation, leaving only a small amount of energy for reproductive performance. However, in the case of energy deficiency for these activities, the dietary or stored proteins or lipids will be catabolized for energy production in the sparing process. Although there is no specified amount for the carbohydrate requirement of broodstock tilapia, many authors have suggested a dietary level of 30%–40% digestible carbohydrate as optimal.
3.6 Vitamins, minerals, and other trace elements
Vitamins are among the most essential micronutrients required by broodstock tilapia. Since they cannot be synthesized in the body due to the lack of the gulonolactone oxidase enzyme, the only route wherein fish can access vitamins is through formulated feeds or supplements. The most common and basic vitamin supplements used in the broodstock diet are ascorbic acid or vitamins C, D, and E, which play important roles in various metabolic activities such as detoxification reaction, steroid synthesis, collagen formation, and stress tolerance. Furthermore, the inclusion of dietary vitamins in broodstock tilapia diet promotes the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which improve vitellogenesis, spawner number, egg hatching, and fry survival rates with improved immune response in females, as well as the synthesis and maintenance of normal sperm, increased motility, and reduced infertility in males. The optimal dietary vitamin requirements of Nile tilapia ranged between 25 and 119 mg/kg diet. However, the exact values vary due to species-specific demands, the presence of antioxidants, and several environmental parameters. For example, in brood tilapia, vitamin C degradation will be accelerated under conditions of hyperoxia, whereas the dietary vitamin E requirements are highly influenced by the dietary lipid levels.
Nutritionally, minerals and trace elements are those inorganic substances required at the micro or macro level for normal physiological functioning, such as in soft tissue and structural skeletal formation, nerve impulse transmission, osmoregulation, growth, reproduction, and healthy body. Moreover, minerals are vital components of many enzymes, hormones, and various metabolic activities. Fishes absorb essential minerals either from their diet or from water. Hence, excess or deficient provision of minerals to fish will affect all of the benefits mentioned above. Conversely, optimal dietary supplements of minerals and trace elements could also be wasted through the interactions and formations of complex products. Thus, their deficiency will inhibit reproductive performance. The dietary provision of minerals and trace elements plays a significant role in improving reproductive performance . For instance, Ca is essential during the sexual maturity of females and is used as a major binding component to the vitellogenin in egg and Ca binding protein. It has been shown that optimal supplementation of Fe, Cu, Zn, and Mg is essential to the regulation of enzymatic and hormonal activities, an enhanced immune system, vitamin synthesis, and improved growth.
In contrast, deficient or excess provisions beyond the required limits will cause toxicity and have adverse effects on the physiology of the fish. Despite the paucity of information and the lack of common agreement on quantifying the level of dietary requirement, several studies recommended provision of trace elements within a certain range to enhance hormonal and enzymatic activities (See table).
Table: Optimal requirements of vitamins, minerals, and trace elements in the broodstock Nile tilapia diet.
| Micronutriment | Dietary required amount |
| Vitamins | |
| Vitamin C | 25–119 mg/kg |
| Vitamin D | 400–420 mg/kg |
| Vitamin E | 120 mg/kg |
| Minerals | |
| Ca | 0.7% |
| Se | 0.21–1.18 mg/kg |
| P | 0.65–0.86 g/100g |
| Mg | 0.2 g/kg |
| Trace elements | |
| Fe | 30–170 mg/kg |
| Cu | 3–5 mg/kg |
| Zn | 32 mg/kg |
| Mn | 13–15 mg/kg |
3.7 Functional additives in brood fish nutrition
Functional additives such as enzymes, hormones, prebiotics, probiotics, and synbiotics are substances that exert benefits for a specific biological function. Hence, supplementing broodstock diet with these additives in different quantities will improve the progeny quality, egg viability, hatching rate, and larval survival. Furthermore, functional additives improve the efficiency of commercial diets in meeting the required nutritional demands by reducing the anti-nutritional factor in the diet. However, the provision of some additives like hormones beyond the optimum level will bring about malformations in larvae. The reproductive performance of fish can potentially be improved through the application of functional feed additives. Probiotics as a feed additive have been demonstrated to have a positive impact on reproductive performance through improving the egg diameter, fecundity, fertilization, egg hatching rate, and juvenile survival rate in fish.
The effect of probiotics in indicating the responsiveness of incompetent follicles to maturation-inducing hormones and changing the oocyte chemical composition during vitellogenic development is well established. The positive role of probiotics in testicular cells has also been validated through their role in upregulating the transcription levels of leptin and the bdnf and dmrt1 genes, hence facilitating spermatogenesis. The importance of phytobiotics as an additive in aquaculture feed is increasingly being recognized, i.e., as one agent that improves the reproductive performance of fishes. Thus, administering prebiotic, probiotic, and synbiotic supplements to broodstock species in adequate amounts will provide health benefits and enhance the performance and overall well-being of fish.
4 Broodstock nutrition and its implication on reproductive efficiency
Physical, chemical, and biological factors strongly affect the reproductive performance of broodstock fish. However, the influence of nutrient composition, such as the energy, lipid, and protein levels, in the diet is an inevitable limiting factor for the maturation, fecundity, and survival of larvae. This includes the availability of essential nutrients that initiate gametogenesis, growth, and reproductive control. Various biomolecules and micronutrients only required in minute amounts play fundamental roles in achieving successful reproductive performance. Nevertheless, dietary nutrient deficiency would lead to failure in reproduction, poor hormonal functioning, and delayed puberty, resulting in common reproductive dysfunctions. The feed must therefore provide tilapia broodstock with optimum protein requirements, essential amino acids, lipid and unsaturated fatty acid intake. In addition, feeding tilapia broodstock on a high-energy diet leads to significant oocyte development, higher fecundity with increased egg diameter, and improved fertility and egg hatch rates.
4.2 Role of Spawner Nutrition on Egg Fertilization in Tilapia
Egg fertilization in aquatic ecosystems is strongly influenced by sperm motility and water chemistry, i.e., salinity and hardness, which make it progressively more difficult for the egg to penetrate. In addition, essential fatty acids, for example EPA and arachidonic acid, present in sperm are closely related to motility and fertilization. Conversely, a delay in the moment of spermiation or ejaculation reduces the fertilization rate because the egg remains in the water for a while, making fertilization more difficult.
Fecundity refers to the total number of eggs in the ovaries of female fish before the next spawning season, which is beneficial in determining egg quality and quantity. However, an imbalance in essential nutrients from the broodstock diet, combined with a decrease in the amount of feed, reduces fertility.
4.3 Role of broodstock nutrition on the embryo development of tilapia
For the normal embryonic development of fertilized eggs, the contributions of essential dietary nutrients such as lipids and vitamins are necessary. The increased level of HUFA such as n-3 in the diet of broodstock reduces the number of morphologically deformed embryos. Because of its phospholipid component, fatty acids play a remarkable role in the structural makeup of numerous biomembranes, enzymes, and cells, and that quality protein consisting of essential amino acids in the diet exerts a significant influence on the embryonic development of larvae.
4.4 Role of broodstock nutrition on the larval quality of tilapia
All essential maternal reserves are transferred into the oocytes during the early stages of ovarian development. Thereafter, the provision of high-quality nutritive feed has a significant role in the improvement of larval quality through increased survival, growth, and swim bladder inflation. Hence, the quality of broodstock diet and its nutritional composition highly determine larval quality until the beginning of exogenous feeding.
5 Conclusions and recommendations
The lack of balanced, nutritive, and formulated diet that improves rapid body growth and other reproductive conditions is the main constraint in commercial aquaculture. The dietary nutrient composition, including lipids and fatty acids, vitamins, minerals, proteins, carbohydrates, and feed size, has a strong influence on the breeding condition and progeny of many broodstock species such as the Nile tilapia.
For successful and profitable aquaculture production, further research focusing on the formulation of a nutritive diet and the implications of each nutritional component, e.g., vitamins, minerals, and trace elements, toward the reproductive performance of broodstock species is recommended.
Source : Engdaw F and Geremew A (2024). Broodstock nutrition in Nile tilapia and its implications on reproductive efficiency. Front. Aquac. 3:1281640.
doi: 10.3389/faquc.2024.1281640
