Continuous or phased biofloc? Optimizing red tilapia reproduction

The application of biofloc technology (BFT) has revolutionized intensive aquaculture, yet its long-term use in broodstock management remains a largely unexplored area. Is it beneficial to maintain red tilapia (Oreochromis spp.) breeders in a continuous biofloc system? A recent study in Aquaculture International delves into this question, revealing that the key to success lies not in constant application, but in a strategic, phased approach that can maximize reproductive efficiency and safeguard fish health.

Broodstock management is a cornerstone of sustainable aquaculture production. Factors such as water quality, nutrition, and environmental stress directly impact gonadal development, hormonal regulation, and ultimately, spawning success. This study evaluated the effects of biofloc technology during the pre-spawning and spawning phases, offering a practical guide for optimizing red tilapia breeding programs.

The study design: A two-phase strategy

To understand the long-term impact of biofloc, researchers from the National Institute of Oceanography and Fisheries (NIOF), Tanta University, Tishk International University, and Alexandria University implemented an experiment divided into two key stages: the pre-spawning (conditioning) phase and the spawning phase. The experiment began with red tilapia fingerlings acclimated to a salinity of 18 ppt, considered optimal for the species under local conditions.

During the spawning period, four treatment groups were established to compare different strategies:

• Control (C-C): Broodstock were maintained in clear water during both phases (pre-spawning and spawning).
• Continuous Biofloc (BF-BF): Broodstock maintained in a biofloc system during both phases.
• Mixed Strategy 1 (C-BF): Maintained in clear water during pre-spawning and transferred to biofloc for spawning.
• Mixed Strategy 2 (BF-C): Maintained in biofloc during pre-spawning and transferred to clear water for spawning.

This design allowed for the isolation of biofloc’s effects at each critical stage of the reproductive cycle.

Pre-spawning phase: The power of biofloc for conditioning broodstock

The results during the pre-spawning phase were conclusive. Fish reared in the biofloc system showed significant improvements compared to those in clear water.

• Enhanced growth and feed efficiency: Broodstock in BFT achieved a higher final weight, weight gain, and specific growth rate. Furthermore, their feed conversion ratio (FCR) was notably lower, indicating more efficient feed utilization, partly because the microbial flocs serve as a supplemental protein source.
• Optimized digestion: The activity of key digestive enzymes such as protease, amylase, and lipase was significantly higher in the BFT group. This suggests improved assimilation of proteins, carbohydrates, and lipids, which is crucial for accumulating the energy reserves needed for reproduction.
• Boosted reproductive maturity: The Gonadosomatic Index (GSI) was significantly higher in BFT females, reflecting greater ovarian development. Both males and females in BFT showed superior gamete quality, with higher sperm counts and lower sperm mortality in males, and a greater number of eggs, larger egg diameter, and higher fecundity in females.

The biofloc system also maintained superior water quality, with lower concentrations of total ammonia nitrogen (TAN), nitrite, and toxic ammonia (NH3​), creating a healthier environment for conditioning.

Spawning phase: The strategic shift that makes the difference

This is where the research reveals its most significant finding. While biofloc was excellent for conditioning, its continuous use during spawning (the BF-BF group) proved to be counterproductive.

The groups that underwent an environmental change (BF-C and C-BF) achieved the best reproductive outcomes:

• Higher egg and fry production: The mixed strategies, particularly C-BF (clear water in pre-spawning, biofloc in spawning), demonstrated the highest number of spawnings per tank, the greatest absolute fecundity, and, crucially, the highest total fry production.
• Improved egg and larval quality: Eggs from the C-BF and BF-C groups had a higher hatching rate (up to 82.7% in C-BF) and greater weight. The resulting larvae were also longer, indicating better nutrient transfer from the mother to the egg, likely due to the nutritional composition of the biofloc.
• Shorter inter-spawning interval: The inter-spawning interval (ISI) was shorter in the C-BF and BF-C groups, which translates to higher reproductive frequency.

The risk of continuous biofloc: Too much of a good thing?

The group maintained continuously in biofloc (BF-BF) exhibited signs of physiological stress and hormonal imbalance. Despite the initial benefits, prolonged exposure to high suspended solids and intense microbial activity appears to negatively affect the broodstock.

This group recorded:

• The longest time to first spawning.
• The lowest fecundity and total fry production.
• Altered levels of reproductive hormones such as FSH and cortisol, indicating stress and a potential suppression of reproductive function.
• Blood and liver indicators suggesting homeostatic imbalance.

Overall health: Biofloc as a protective shield

Beyond reproduction, the study confirms that biofloc has a potent protective effect on fish health.

• Strengthened immune system: Fish in BFT treatments (especially C-BF and BF-C) showed improved immune parameters, such as higher levels of total protein, globulins, lysozyme, and immunoglobulin M (IgM).
• Lower bacterial load: Researchers reported a drastic reduction in intestinal pathogenic bacteria like E. coli, Salmonella sp., Shigella sp., and Aeromonas sp. in the BFT groups, particularly in females. This demonstrates the probiotic and competitive exclusion effect of the biofloc microbial community.
• Improved liver and kidney function: Levels of liver enzymes (AST, ALT), which are indicators of stress or cellular damage, were significantly lower in the BFT groups, as were markers of renal function like urea and creatinine.

Conclusion: The recommended strategy for producers

This study conclusively demonstrates that biofloc technology is a powerful tool for red tilapia broodstock management, but its effectiveness depends on intelligent application.

The recommendation for producers is to adopt a phased strategy:

1. Utilize the biofloc system during the pre-spawning (conditioning) phase. This capitalizes on its benefits for improving growth, feed efficiency, gamete quality, and the overall condition of the broodstock.
2. Transfer the broodstock to a clear water system during the spawning phase. This change prevents the physiological stress and hormonal imbalances associated with prolonged exposure, allowing the fish to optimally channel their accumulated energy into spawning.

This strategic approach allows producers to maximize the benefits of biofloc (nutrition, water quality, pathogen control) while minimizing its long-term risks, thereby ensuring a more efficient, healthy, and sustainable production of fry.

Contact
Mohammed F. El Basuini
Faculty of Agriculture, Tanta University
Tanta City, 31527, Egypt
Email: mohammed.elbasuini@agr.tanta.edu.eg

Akram Ismael Shehata
Department of Animal and Fish Production, Faculty of Agriculture (Saba Basha), Alexandria University
Alexandria City, 21531, Egypt
Email: akramismael2@gmail.com

Reference (open access)
Sallam, G.R., El Basuini, M.F., Alhoshy, M. et al. Strategic application of biofloc technology for optimizing physiological homeostasis and reproductive efficiency in red tilapia (Oreochromis spp.) broodstock under long-term rearing conditions. Aquacult Int 33, 464 (2025). https://doi.org/10.1007/s10499-025-02141-2

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.