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?

1. A

   Only one

   Only one. Nitrification in the biofilter is the core job; uneaten feed is mechanical, not biofilter.

2. B

   Only two

   Only two. Biofilters convert ammonia to nitrate. They do not primarily remove uneaten feed, and they do not dose phosphorus for fish.

3. C

   All three

   All three. Phosphorus is not increased as a nutrient service of the biofilter.

4. D

   None

   None. Ammonia-to-nitrate is textbook RAS.

Summary. Official key is (b) only two. In a recirculating aquaculture system the biofilter is a nitrifying bed: ammonia → nitrite → nitrate. Solids / uneaten feed are settled or screened first. The unit does not add phosphorus as fish food.