With reference to the role of biofilters in Recirculating Aquaculture System, 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 nutrient for fish in water.
How many of the statements given above are correct?
Answer & explanation
Answer: (b) Only two
Statements 1 and 2 are counted as correct, and statement 3 is wrong. A biofilter is the waste-treatment unit of a recirculating fish farm: its bacteria turn toxic ammonia from fish waste and feed into less harmful nitrate, and it does not add phosphorus.
- ✓ 1. Waste treatment in a recirculating system includes removing waste solids, both faeces and uneaten feed, and the biofilter is part of that treatment train. Strictly, the mechanical filter removes solids and the biofilter handles dissolved nitrogen; UPSC's key counts this statement as correct.
- ✓ 2. Nitrifying bacteria in the biofilter convert ammonia into nitrite and finally into nitrate, which is far less toxic to fish than ammonia.
- ✗ 3. The biofilter removes toxic ammonia; it does not add phosphorus. Phosphate is an inert dissolved compound that simply passes through the filtration stage.
Remember · In a recirculating aquaculture system, the biofilter's nitrifying bacteria convert toxic ammonia to nitrite and then to less toxic nitrate. It adds no phosphorus.
Sources
- ICAR-CMFRI Training Manual Series No. 28 (2022), Recirculating aquaculture systems: waste treatment unit processes ↗ · reference work “include the removal of waste solids (both faeces and uneaten feed), the conversion of ammonia and nitrite-nitrogen (a non-toxic form of dissolved nitrogen), the addition of dissolved oxygen to the water … Nitrifying bacteria convert ammonia into nitrite and finally into nitrate. … Phosphate is an inert substance, with no toxic effect, but nitrogen in the form of free ammonia (NH3) is toxic and needs to be transformed into non-toxic form in the bio-filter.”
Question and answer: UPSC's official GS Paper I (2023, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·