📌 The Question

With reference to the role of biofilters in Recirculating Aquaculture Systems (RAS), consider the following statements:

1. Biofilters provide waste treatment by removing uneaten fish feed.
2. Biofilters convert ammonia present in fish waste to nitrate.
3. Biofilters increase phosphorus as a nutrient for fish in water.

How many of the statements given above are correct?

(a) Only one
(b) Only two
(c) All three
(d) None

✅ Correct Answer: (b) Only two

🧑‍🏫 Classroom Explanation

Statement 1 is correct
Recirculating Aquaculture Systems are closed-loop, tank-based systems where water is reused after treatment. Biofilters host beneficial microorganisms that help break down organic waste, including uneaten feed and dissolved organic matter, thus improving water quality.

Statement 2 is correct
Fish excrete ammonia, which is highly toxic. Biofilters support nitrifying bacteria:

• Nitrosomonas convert ammonia → nitrite
• Nitrobacter convert nitrite → nitrate
  Nitrate is far less toxic and can be safely managed within the system.

Statement 3 is not correct
Biofilters do not increase phosphorus. In fact, they help remove phosphorus-rich waste products, preventing nutrient buildup and eutrophication risks.

⚡ Curiosity Raiser

Can tiny bacteria quietly replace rivers, wetlands, and oceans inside a tank? 🐟

📚 Enrich Notes (UPSC Edge)

• RAS = Water-efficient + pollution-controlled aquaculture
• Biofilters perform:
  • Biological nitrification
  • Detoxification of ammonia
  • Reduction of nutrient discharge
• Widely used in:
  • Urban aquaculture
  • High-density fish farming
  • Regions with water scarcity
• Aligns with Blue Economy & Sustainable Fisheries

🕊️ IAS Monk Whisper

“When nature is miniaturized with wisdom, sustainability becomes a system—not a slogan.”