This study aimed to determine the protein requirements of the fattening phase for Nile tilapia (Oreochromis niloticus) fed fish meal-free diets. A total of 75 Nile tilapia were maintained in a water recirculation system, and five isoenergetic diets were formulated with increasing protein levels encompassing three repetitions each. The findings revealed that protein levels significantly affected certain Nile tilapia performance, yield, and composition parameters. The determined parameter values clearly indicated that Nile tilapia can be fed fish meal-free soybean meal and corn-based diets. Furthermore, the metabolic plasticity of this species concerning dietary protein concentrations was also demonstrated, with adequate performance results achieved in treatments containing from 267 to 294 g/kg digestible protein (DP), or 298 to 327 g/kg crude protein (CP), where the balance between essential and non-essential amino acids and energy resulted in adequate performance correlated to satisfactory feed conversion values and filet yields and composition. A DP concentration of 267 g/kg (298 g/kg CP) is recommended when offering corn and soybean meal-based diets during the Nile tilapia fattening phase to fish weighing between 400 and 700 g.
1. Introduction
Aquaculture plays a fundamental role in ensuring global food security and is the food production sector that has expanded the most in the last 50 years, with total fish production growth estimates of over 15% by 2030. In this sense, Nile tilapia (Oreochromis niloticus) stands out as the third most cultivated species, contributing to 9% of the 2020 global production. About 92% of the worldwide production of this species employs commercial feed, representing around 70% of total production costs.
Among basic tilapia feed nutrients, protein stands out as a fundamental dietary component, significantly affecting Nile tilapia performance. Inadequate digestible protein (DP) levels can result in several issues, such as reduced feed consumption, consequently compromising fish growth.
Protein is an essential component in the construction and maintenance of cellular structures, tissues, and organs, playing a crucial role in metabolic processes. When ingested, proteins undergo a hydrolysis process, and part of the derived amino acids are absorbed, following several possible metabolic pathways. The nitrogen resulting from oxidative amino acid processes is then excreted into the water in the form of ammonia (NH3), which can cause significant environmental impacts, contributing to issues such as eutrophication and other negative water quality effects. Therefore, fish diet formulations should be adjusted to meet the specific needs of each species, ensuring an adequate nutrient balance to optimize animal growth and health and minimize negative environmental impacts.
Recently, several studies have determined the optimal levels of dietary protein for Nile tilapia at different stages of development: 318 ± 6.50 g/kg [12,13,14,15,16], 292 ± 18.19 g/kg [17,18,19,20,21], and 255 ± 16.5 g/kg [6,22,23] for tilapia with an average final weight of 12 ± 2.5 g, 57 ± 2.39 g, and 415 ± 3.37 g, respectively. These requirements are lower than those presented in the NRC (2011) [7], where fish with an average weight of less than 20 g, from 20 to 200 g, and from 200 to 600 g have a requirement of 400, 340, and 300 g/kg of crude protein, respectively. In this sense, it is worth noting that the evolution of the tilapia production chain, combined with the use of new strains with higher productivity, demands new studies to better meet the nutritional requirements of this species. In addition, there is a lack of studies on protein requirements in the fattening phase for fish with an average weight above 500 g.
To meet these nutritional requirements, fish meal has been recognized as the most appropriate protein source option for this species, due to its high nutritional value and palatability. However, in addition to its production having plateaued for some years, reduced fish meal availability was noted between 2018 and 2020, contradicting market demands. This decline, driven by rapid aquaculture production growth and use by other animals, has led to significant fish meal price increases.
In this sense, plant protein sources have emerged as a promising alternative, capable of partially or fully replacing fish meal in Nile tilapia diets. This approach not only provides satisfactory results in terms of performance and immune response enhancement but also contributes to reduced total feed costs.
In general, studies investigating the protein needs of tilapia employing fish meal-free feed have reported positive results compared to other studies assessing similar developmental stages but employing diets containing animal ingredients. The developmental stage of the fish directly influences their protein requirement, with a tendency for this requirement to decrease with the increasing weight and age of the fish. However, when evaluating studies conducted on the protein requirement of Nile tilapia, Meurer et al. (2024) identified that these studies have focused on the early developmental stages of this species, with the few studies conducted during the fattening phase (with a final average weight above 500 g) showing a tendency for an increase in the protein requirement compared to the growth phase of these fish. Additionally, although it has been scientifically proven that it is possible to use fish meal-free feed in Nile tilapia feeding, no study has been conducted on this developmental phase. Therefore, this study aimed to determine Nile tilapia fattening phase protein requirements employing fish meal-free diets.
2. Materials and Methods
This study was carried out at the Aquaculture Technology Laboratory (Lataq) belonging to the Federal University of Paraná (UFPR), located at the Advanced Jandaia do Sul Campus (PR, Brazil). The experimental procedure protocol was approved by the UFPR Palotina Sector Ethics Committee on the Use of Animals (Protocol n. 05/2021—CEUA/Palotina).
2.1. Fish Subjects and Experimental Design
The experiment lasted 84 days, beginning at the end of December 2022. A total of 75 adult Nile tilapia (Genetically Improved Farmed Tilapia—GIFT lineage) with an average initial weight of 412 ± 8.06 g were acclimatized for 60 days. After this period, the fish were anesthetized by immersion in a 50 mg/L eugenol solution, weighed, and randomly distributed into five treatments encompassing three repetitions each.
A recirculating aquaculture system (RAS) consisting of 15 circular 1000 L tanks installed in a cultivation greenhouse was used. The tanks were connected to a 2000 L mechanical filtration tank and a 30,000 L biofiltration tank. Each 1000 L tank was considered an experimental unit. A water recirculation rate of 12 times a day was maintained in each experimental unit during the experiment. The 1000 L tanks were aerated using a porous hose connected to an air system that was connected, in turn, to a 0.5 hp radial blower, with an individual water inlet and outlet.
All experimental units were equipped with a self-siphoning system at the bottom of the tank, with a centralized slope of 5% and a central outlet for the removal of feces and other waste. The mechanical filtration and biofiltration tanks were siphoned weekly (500 L) to remove residues. The biofiltration tank was partly occupied by Eichornia crassipes, which were removed as necessary, maintaining between 50% and 80% total coverage.
2.2. Experimental Diets and Fish Feed Management
Five experimental fish meal-free diets were formulated, namely isoenergetic, isocalcium and isophosphoric, mainly composed of soybean and corn meal and containing increasing DP levels (216, 244, 268, 294 and 316 grams per kg). DP, digestible energy (DE), and the calculated composition of essential amino acids were determined. The experimental diets were weighed daily and provided equally to the fish in all experimental units in two daily feedings, one at 8 a.m. and the other at 5 p.m.
3. Results
3.1. Zootechnical Performance
The zootechnical performance results of Nile tilapia fed fish meal-free diets containing increasing protein levels during the fattening phase are presented in Table 3. The offered protein levels significantly influenced (p < 0.05) WG (Weight Gain) , DWG (Daily Weight Gain), SGR (Specific Growth Rate), FCR (Feed Conversion Ratio), and PER( Protein Efficiency Ratio). Better WG, DWG and SGR results were observed in the T27 and T29 treatments. The worst result was noted for the T22 diet, and the T24 and T32 diets did not differ from each other or from the other treatments.
Figure 1. Feed conversion of Nile tilapia fed diets containing different concentrations of DP (a) and CP (b) during the fattening phase, analyzed using the combination of linear-plateau regression (broken-line) and quadratic polynomial regression models.
3.2. Body yield
Fillet yield (FR) (Figure 2) showed a quadratic effect with increasing dietary protein, with a maximum value of 281.45 g/kg PD and 314.19 CP. When analyzing the same parameter using a combination of linear-plateau (broken line) and quadratic polynomial regression models, the intercepts of the lines indicated a value of 256.78 g/kg PD and 286.20 g/kg CP (Figure 2a,b).
Fig 2. Fillet yield of Nile tilapia fed diets containing different concentrations of DP (a) and CP (b) during the fattening phase, analyzed using a combination of linear-plateau regression (broken-line) and quadratic polynomial regression models.
4. Discussion
Proteins, alongside peptides, are composed of amino acids. Thus, protein requirements, whether crude or digestible, should be ultimately translated in terms of amino acid requirements. Amino acids can be essential or non-essential, with their essentiality correlated to the possibility of a given individual’s capacity to synthesize these elements in adequate amounts, which may vary according to growth phase or a specific momentary physiological situation. The importance of assessing protein levels should, thus, be verified, as amino acid requirements should be the preferred parameters. However, protein assessments are made easier by the fact that their analyses are much cheaper than amino acid assessments and can be performed easily in feed mills. Furthermore, specifically concerning this study, soybean meal composition values vary only slightly [36]. Thus, when compared to other ingredients, feeds formulated with these ingredients allow for adequate indirect amino acid-level estimates.
Nile tilapia performance is directly influenced by dietary protein levels, which are, in turn, associated with several biochemical and physiological processes that directly affect fish growth, development, and health. Proteins play crucial roles in tissue synthesis, metabolic regulation, immune responses, and other vital fish organism functions. Therefore, if fish are offered inadequate dietary protein amounts or imbalanced essential amino acids, protein synthesis can be compromised, negatively affecting performance indices. This was evidenced herein by the data analysis according to the Tukey test or the linear-plateau (broken-line) and quadratic polynomial regression models (Figure 1 and Figure 2), which revealed that both the lowest and the highest protein levels were associated with Nile tilapia performance declines. This non-linear response highlights the need for precise dietary formulations, highlighting that adequate protein levels are essential to optimize Nile tilapia growth and body composition. This, in turn, suggests an optimized Nile tilapia response to a specific DP concentration, indicating the importance of adequate diet formulations to maximize fish growth rates during the fattening phase.
As stated previously, our findings indicate that varying the dietary protein concentrations significantly influences Nile tilapia performance indices. The T27 treatment resulted in the highest values for several of the assessed variables. These results are in line with previous studies indicating tilapia sensitivity to diet composition variations, especially concerning DP.
5. Conclusion
Based on the study results and the parameters evaluated, Nile tilapia can indeed be fed a soybean- and cornmeal-based, fishmeal-free diet. Results also verified the species’ metabolic plasticity concerning dietary protein concentrations, with adequate performance results noted for DP treatments containing 268 to 294 grams per kg, or 298 to 327 grams per kg CP. In this sense, the balance between essential and non-essential amino acids and energy results in adequate Nile tilapia performance correlated to good feed conversion values, fillet yields and composition. Overall, a DP concentration of 267 grams per kg (298 grams per kg CP) is recommended for Nile tilapia that are fed a corn or soybean meal-based diet and that weigh between 400 and 700 grams in the grow-out phase.
Source : Novodworski, J.; Matos, É.J.A.; Gonçalves, R.M.; Bombardelli, R.A.; Meurer, F. Protein Requirements of Fattening Nile Tilapia (Oreochromis niloticus) Fed Fish Meal-Free Diets. Aquac. J. 2024, 4, 135-147. https://doi.org/10.3390/aquacj4030010
