Nanobubbles (NBs) are ultra‑fine gas bubbles (<100–1000 nm) with high internal pressure and surface charge that remain suspended in water for extended periods. Compared to conventional macro- or microbubbles, NBs dissolve slowly and enhance gas transfer efficiency, often yielding much higher oxygen transfer (70–90% efficiency) than traditional aeration.
In live fish transport, NB technology (typically oxygen or ozone NBs) can maintain a near-saturated DO level (~8–9 mg/L) for much longer, reducing hypoxia, ammonia build-up, and physiological stress. For example, a recent trial with rainbow trout fingerlings over a 12 h transport period showed survival >99% with NB aeration versus ~65–90% with conventional aeration. Ozone NBs also reduced bacterial loads with minimal gill damage. Nanobubble systems promise lower oxygen use and energy costs (e.g. ≥ 30–75% savings in O₂) while simultaneously improving animal welfare and water quality.
Nanobubble Definitions and Physics
Nanobubbles are gas-filled cavities in water with diameters typically below 200 nm. They include bulk nanobubbles (freely suspended in the liquid) and surface nanobubbles (attached to surfaces). Unlike larger bubbles which quickly rise to surface and burst, nanobubbles have extremely high internal pressure (governed by Laplace’s law) and carry a large negative surface charge (high zeta potential), this charge prevents coalescence and allow them to persist suspended and dispersed in water for days to weeks. These physical traits give NBs a huge surface-area-to-volume ratio and a very slow rise velocity.
As a result, NBs provide enhanced mass transfer of gases (O₂, O₃) into water. Compared to conventional bubbles, nanobubbles yield much higher gas dissolution efficiency and can even generate reactive oxygen species (hydroxyl radicals) in situ. For example, nanobubble infusions have been shown to maintain DO levels far longer than normal aeration: dissolved O₂ can increase much faster and stay elevated. In aquaculture, stable, oxygen‑rich nanobubble water can boost fish growth and survival by enabling continuous oxygen delivery without significant gas losses.
Mechanisms of NB Effects
Dissolved Oxygen and Gas Transfer: Nanobubbles substantially increase the rate and efficiency of O₂ dissolution. Their high surface area and prolonged suspension allow near-constant O₂ diffusion into water. Compared to macro aeration, NB systems can raise DO levels several-fold faster and maintain elevated DO even under high fish respiration. In transport trials, NB aeration kept DO around 8–9 mg/L for hours, whereas conventional aeration or static O₂ dropped to 4–5 mg/L. This continuous high-DO environment prevents hypoxia.
Oxidative Chemistry and Stress: Oxygen nanobubbles can generate low levels of reactive oxygen species (ROS) like hydroxyl radicals, especially under UV or turbulence. These ROS can help break down organics and pathogens, but might pose oxidative stress if excessive. NB systems use pure O₂ or air; the ROS effect mainly aids water “self‑purification” without harming fish.
Pathogen Control and Biofilm Removal: Nanobubble treatments (air or O₃ NBs) are reported to inactivate bacteria, viruses, and algae. Review studies note that air/ozone NBs “demonstrated effective control of infectious bacteria and viruses”. Laboratory tests with ozone NBs showed rapid reduction of Vibrio and other pathogens without harming shrimp or fish. The hypothesized mechanism is involved in oxidative damage to microbes and improved microbial metabolism in biofilters. In transport, reducing pathogen load (e.g. via brief O₃ NB pulses) could lower infection risk.
Fish Physiology and Stress. Stable oxygenation and water quality benefit fish health. High DO keeps metabolism aerobic and suppresses stress hormones (cortisol) associated with hypoxia. Lower ammonia also reduces toxicity. NB aerated fish experienced near zero mortality, whereas conventionally-oxygenated fish faced heavy losses. Preliminary data suggest NB-exposed fish may exhibit lower cortisol and lactate, reflecting lower stress.
Overall, NB aeration is believed to reduce transport stress by avoiding hypoxia and toxin buildup.
Comparison with Conventional Aeration/Oxygenation
Traditional transport systems use aeration stones with air or pure O₂ injection. Pure-O₂ systems often produce extremely high saturation (>150–200%), which must be relieved slowly to avoid gas-bubble disease. NB technology seeks to match or exceed pure-O₂ performance more safely. In head to head trials, NB aeration achieved higher DO as pure O₂, but with much lower O₂ use. Reports suggest NB systems can cut O₂ consumption by 30–75% compared to standard bubble oxygenation. Mechanistically, NBs dissolve oxygen efficiently without large free bubbles, whereas conventional air stones waste ~50–90% of oxygen to the air.
In head-to-head trials, NB treatment usually yields far better survival than conventional methods. Devkota et al. found NB aeration (with O₂) boosted trout survival to ~99%, whereas conventional O₂ aeration or pure-O₂ packing only gave ~65–90%. These differences likely stem from NBs’ ability to maintain stable DO and remove CO₂ and NH₃ more effectively. No study showed NB performing worse than traditional aeration.
Conclusion
Nanobubble technology offers a promising approach to improving the efficiency and reliability of live fish transport by maintaining stable dissolved oxygen levels, enhancing gas transfer, and improving overall water quality throughout the transport period. Unlike conventional aeration, nanobubbles remain suspended in water for extended durations, allowing oxygen to be delivered more efficiently while reducing oxygen wastage. This sustained oxygen availability helps minimize hypoxia, limits ammonia accumulation, and reduces physiological stress on transported fish.
Experimental studies have consistently reported higher survival rates with nanobubble-based transport systems compared with conventional aeration, particularly during long transport durations. In addition to improving oxygenation, ozone nanobubbles have demonstrated the ability to reduce microbial loads, offering an added benefit for maintaining hygienic transport conditions. The technology also shows potential for lowering oxygen consumption and operating costs without compromising fish welfare.
Although transport performance ultimately depends on factors such as species, stocking density, transport duration, temperature, and water quality, current research indicates that nanobubbles can serve as an effective process enhancement for live fish transport. Nanobubbles are expected to play an increasingly important role in improving transport efficiency, animal welfare, and the sustainability of aquaculture operations.
References
- Nirmalkar, N., Pacek, A. W., & Barigou, M. (2018). On the existence and stability of bulk nanobubbles. Langmuir, 34(37), 10964–10973.
- Devkota, H. R., Jha, D. K., Joshi, T. P., Shrestha, S., & Bhandari, M. P. (2023). Enhancing the Survival Rate in Live Fish Transport by Utilizing Nanobubble Technology. Nepalese Journal of Aquaculture and Fisheries, 10(1), 33–42.
- Yaparatne, S., Morón-López, J., Bouchard, D., Garcia-Segura, S., & Apul, O. G. (2024). Nanobubble applications in aquaculture industry for improving harvest yield, wastewater treatment, and disease control. Science of the Total Environment, 931, 172687.
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- Jhunkeaw, C., et al. (2021). Ozone nanobubble treatments improve survivability of Nile tilapia (Oreochromis niloticus) challenged with a pathogenic multi-drug-resistant Aeromonas hydrophila. Journal of Fish Diseases.
- Meegoda, J. N., Hewage, S. A., & Batagoda, J. H. (2018). Stability of Nanobubbles. Environmental Engineering Science, 35(11), 1216–1227.
- Wang, X., et al. (2023). Mechanisms on stability of bulk nanobubble and relevant applications: A review. Journal of Cleaner Production, 426, 139153.