🌊 How Oxygen Levels Shape Microbial Communities in Aquaculture

Yes, we are still talking about oxygen in this second bulletin!

In aquaculture, dissolved oxygen (DO) isn’t just another water quality metric, it’s the lifeline of your system.
Hypoxia usually means <3 mg/L, but many sensitive species will already be stressed above that threshold.

What Happens Under Low DO?

• Microbial shift: Beneficial aerobic bacteria (your waste-processing “clean-up crew”) slow down. Anaerobes step in, leaving behind toxic byproducts — ammonia, nitrite, hydrogen sulfide, methane.

• Nitrification stalls: Nitrosomonas and Nitrobacter can’t function well, so ammonia and nitrite accumulate, stressing or even killing stock.

• Pathogens rise: Vibrio and Aeromonas (facultative anaerobes) thrive in low oxygen, while fish and shrimp immunity collapses.

• Algal boom-and-bust: Algal die-offs dump organic matter, driving DO even lower — a vicious cycle that favors disease.
  
  

Think of it like a crowded nightclub where the bouncers (aerobic microbes) step outside for a smoke break… and suddenly the troublemakers (pathogens) slip in and take over the dance floor.

🔑 Key Takeaways for Farmers

• Keep DO safely above 5 mg/L.

• Invest in proper aeration and circulation.

• Avoid overfeeding and manage organic load.

• Probiotics (aerobic strains) help — but only if there’s enough oxygen for them to work!

• Monitor DO at night and early morning when photosynthesis shuts down and respiration dominates.

💡 Bottom line: In aquaculture, oxygen is your best insurance policy. Lose it, and you don’t just lose water quality — you hand pathogens the upper hand.

🫧 Water oxygenation in fish farming: a topic too often overlooked

⁉️ The title of this post can seem paradoxical: why would fish farmers neglect a parameter that can lead in a few hours to the loss of one, or even several years of hard work?

🐟 Because in some fish farms such a disaster actually never happens: the water renewal rate is high enough compared to the density of fish to prevent any massive mortality event. Recently, we visited a fish farm where water oxygenation was not monitored, and no device was used to increase water oxygen concentration, except a few paddle wheels.

‼️ We were surprised to see that some fish were more than a decade old, proving that such a set-up can work without any accident happening for many years, although the climate is tropical. However, this is only the tip of the iceberg…

🔎 After discussing with the farmers, they told us that the fish growth was underwhelming, and that they were facing chronic health issues (notably skin lesions). We also observed that the fish were rather lethargic, with a low appetite: they were wasting the feed that was supplied to them.

📉 This is the hidden part of the hypoxia iceberg! The lack of oxygen is often not a sudden killer, but a chronic one that silently saps performance! The water oxygen concentration is high enough for animals to survive, but already too low for them to fulfill all their necessary biological functions…

The sublethal effects of hypoxia notably include:

1️⃣ Reduced swimming activity

2️⃣ Degraded growth and feed efficiency, high feed wastage

3️⃣ Lower fertility

4️⃣ Impaired embryonic development and high mortality in juveniles

5️⃣ Weaker immune system leading to a surge of disease outbreaks

6️⃣ Higher secretion of cortisol (stress hormone)

👍 Fortunately, many tech tools now exist to end hypoxia: IoT-based systems that track oxygenation with high precision, AI programs that detect suspicious patterns, and nanobubble generators that ensure efficient and long-lasting oxygenation.

If these issues sound familiar to you, do not hesitate to contact us!