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UPSC Prelims 2023 · Environment · Species Watch
With reference to the role of biofilters in Recirculating Aquaculture System, consider the following statements: How many of the statements given above are correct?
- Biofilters provide waste treatment by removing uneaten fish feed.
- Biofilters convert ammonia present in fish waste to nitrate.
- Biofilters increase phosphorus as nutrient for fish in water.
- (a) Only one
- (b) Only two
- (c) All three
- (d) None
Show the answer and explanation
Answer: (b) Only two
Waste treatment and ammonia-to-nitrate conversion are right; biofilters don’t add phosphorus for fish.
Statement by statement
1. ✓ CORRECT The biofilter helps treat waste, including breaking down uneaten feed and organic matter.
2. ✓ CORRECT Nitrifying bacteria convert ammonia → nitrite → nitrate, which fish tolerate far better.
3. ✗ WRONG Biofilters don’t add phosphorus; excess phosphorus is a pollutant to be removed.
The idea
In a recirculating system the same water is cleaned and sent back to the fish tank again and again. The danger is ammonia from fish waste and rotting feed, which is poisonous to fish. The biofilter is a bed of helpful bacteria that changes ammonia into nitrate, which fish can tolerate.
Water leaves the fish tank → Solid waste is strained out → Biofilter bacteria: ammonia → nitrite → nitrate → Oxygen is added → Water returns to the tank
The trap
Fish do need phosphorus in feed; the error is that a biofilter adds it.
Also know
These are the same nitrifying bacteria that work in soil. If plants are grown on the nitrate-rich water, the system is called aquaponics. Such systems save water and land and are promoted under the national fisheries scheme.
🔒 RAS biofilter = nitrifying bacteria: ammonia → nitrite → nitrate.