Study determines the ideal protease dosage to enhance tilapia growth

There is a constant search for strategies to improve the efficiency and sustainability of aquaculture. One of the greatest challenges is optimizing the use of protein in feed, the most expensive component of the diet. A recent scientific study by researchers from the Universidade Federal de Santa Maria (UFSM) evaluated the impact of an exogenous protease in the diet of Nile tilapia (Oreochromis niloticus) juveniles, revealing not only significant performance improvements but also the optimal dosage to achieve them.

Key findings

• The addition of exogenous protease to the diet significantly improves the productive performance of Nile tilapia juveniles.
• The optimal dose to maximize relative weight gain was estimated at 440 mg/kg of feed (equivalent to 33,000 U/kg).
• The protease increased protein and lipid retention and bodily deposition, indicating better utilization of dietary nutrients.
• At a genetic level, the inclusion of 390 mg/kg of protease upregulated the expression of the growth hormone receptor (GHR) gene in the liver, which is directly linked to enhanced growth.
• The use of the enzyme produced no negative effects on hematological and physiological health indicators, proving to be a safe and effective strategy.

The protein challenge and the role of enzymes

Traditionally, fishmeal has been the premier protein source in aquaculture, but its availability is limited and its cost is high. This has driven the use of alternative ingredients like soybean meal and animal by-products (e.g., feather meal, fish residue meal). However, these sources may contain less digestible components that limit their utilization by fish.

This is where exogenous enzymes like protease come into play. These enzymes supplement the action of the fish’s own digestive proteases, helping to break down complex proteins into simpler components such as free amino acids and oligopeptides, thus facilitating their absorption and use.

How was the effect of protease evaluated?

To determine the ideal dosage and its effects, researchers conducted a 49-day experiment using 300 Nile tilapia juveniles with an average initial weight of 5.69 grams.

The researchers formulated a control extruded diet and, from it, created four experimental diets supplemented with different concentrations of a commercial protease (Ronozyme ProAct):

• 194 mg/kg
• 316 mg/kg
• 390 mg/kg
• 600 mg/kg

Throughout the trial, parameters for growth performance, feed efficiency, body composition, blood indicators, and the expression of growth-related genes were measured.

Direct impact on growth and feed efficiency

The results demonstrated a clear benefit from using the protease.

• Significant performance improvements: Fish fed the diet containing 390 mg/kg of protease showed superior performance compared to the control group (without protease). This was reflected in a higher final weight, daily weight gain, and better feed and protein efficiency ratios.
• Determining the optimal dose: Using a quadratic regression analysis, the study calculated that the optimal inclusion level of protease to achieve maximum relative weight gain (RWG) is 440 mg/kg of feed. This data is crucial for feed formulators seeking to maximize zootechnical performance.

Beyond growth: Nutrient retention and gene expression

The effect of the protease was not limited to weight gain.

• Improved protein and lipid utilization: Supplementation with the enzyme significantly improved both protein and lipid retention and bodily deposition. The 390 mg/kg group, for example, exhibited higher protein and lipid retention compared to the control group. This indicates that the enzyme allows fish to more efficiently use nutrients from the feed to build body tissue.
• Stimulation at the genetic level: A highly relevant finding was the protease’s effect on the expression of growth-regulating genes. Fish that consumed the diet with 390 mg/kg of protease showed higher expression (upregulation) of the growth hormone receptor (GHR) gene in the liver. This receptor is key in the somatotropic axis that regulates growth, and its increased expression is directly associated with the observed performance improvements.

Health effects: Blood and metabolic indicators

The study also confirmed that protease inclusion is a safe practice.

• Blood health: Researchers observed a positive linear effect on the number of red blood cells (erythrocytes) as the protease dose increased. This suggests a greater oxygen-carrying capacity to support faster growth, without adverse effects on other hematological parameters.
• Efficient protein metabolism: The protease promoted a more efficient use of amino acids. While the concentration of amino acids in plasma decreased with high doses of the enzyme, their concentration in tissues (liver and muscle) increased. Concurrently, the ammonia content in these tissues decreased.

Collectively, these results suggest that amino acids were being used effectively for protein synthesis and growth, rather than being catabolized and excreted as ammonia. This is not only beneficial for the fish but also for the culture water quality.

Conclusion

Supplementing diets for Nile tilapia juveniles with protease (Ronozyme ProAct) is an effective strategy for improving productive performance. The study concludes that the optimal dosage to maximize weight gain is 440 mg/kg. This inclusion not only enhances growth and feed efficiency but also improves nutrient retention and positively modulates the expression of key growth-related genes, all without compromising the physiological health of the fish.

These findings offer a valuable tool for the aquafeed industry, enabling the formulation of more efficient and sustainable diets that make better use of alternative protein sources.

Contact
Thamara Luísa Staudt Schneider
Programa de Pós-Graduação em Zootecnia, Universidade Federal de Santa Maria (UFSM)
Campus Sede, Santa Maria 97105-900, Brazil
Email: thamara.schneider@acad.ufsm.br

Reference
Schneider, T. L. S., Hermes, L. B., Schmidt, M. R., Loureiro, B. B., Peixoto, N. C., Graichen, D. A. S., & Lazzari, R. (2025). Protease improves performance, GHR gene expression, nutrient deposition, hematological, and biochemical indicators of Nile tilapia. Animal Feed Science and Technology, 329, 116496. https://doi.org/10.1016/j.anifeedsci.2025.116496

Milthon Lujan

Editor at the digital magazine AquaHoy. He holds a degree in Aquaculture Biology from the National University of Santa (UNS) and a Master’s degree in Science and Innovation Management from the Polytechnic University of Valencia, with postgraduate diplomas in Business Innovation and Innovation Management. He possesses extensive experience in the aquaculture and fisheries sector, having led the Fisheries Innovation Unit of the National Program for Innovation in Fisheries and Aquaculture (PNIPA). He has served as a senior consultant in technology watch, an innovation project formulator and advisor, and a lecturer at UNS. He is a member of the Peruvian College of Biologists and was recognized by the World Aquaculture Society (WAS) in 2016 for his contribution to aquaculture.