📘 Q.13 IAS Prelims 2023 — Environment & Ecology (Recirculating Aquaculture Systems)
📌 The Question
With reference to the role of biofilters in Recirculating Aquaculture Systems (RAS), consider the following statements:
- Biofilters provide waste treatment by removing uneaten fish feed.
- Biofilters convert ammonia present in fish waste to nitrate.
- 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.”