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 above statements are correct?

1. Biofilters provide waste treatment by removing uneaten fish feed. In RAS, biofiltration is part of the waste-treatment train and helps improve water quality by processing organic waste associated with fish culture; UPSC appears to treat this broadly as part of biofilter-based waste treatment. Verdict: Correct (as per exam framing).

2. Biofilters convert ammonia present in fish waste to nitrate. This is the core function of biofilters in RAS: nitrifying bacteria convert ammonia -> nitrite -> nitrate. Verdict: Correct.

3. Biofilters increase phosphorus as nutrient for fish in water. Biofilters are not designed to enrich water with phosphorus; their main role is waste conversion/removal, especially nitrogenous waste. Verdict: Incorrect.

Hence, two statements are correct. Answer: (b).

Disclaimer: Technically, uneaten feed is usually removed mainly by mechanical filtration/solids removal, so Statement 1 is somewhat loosely worded. But given the official UPSC key, Statement 1 is being interpreted in a broader waste-treatment sense.