Detailed Explanation:

Answer: Option 2 — Only two

This question tests understanding of biofilter functions in Recirculating Aquaculture Systems (RAS). Out of three statements, two are correct regarding waste treatment and ammonia conversion, while the statement about phosphorus is incorrect.

✅ Statement 1 – Correct: Biofilters provide waste treatment by removing uneaten fish feed and organic matter, as beneficial bacteria on biofilter media break down these wastes.

✅ Statement 2 – Correct: Biofilters convert toxic ammonia from fish waste to less harmful nitrate through the nitrification process performed by beneficial bacteria (ammonia → nitrite → nitrate).

❌ Statement 3 – Incorrect: Biofilters do not increase phosphorus levels in water; their primary role is waste removal and ammonia conversion, while phosphorus management is handled through feed formulation and water quality control.

📝 Short Notes: Recirculating Aquaculture System (RAS) and Biofilters

• RAS Definition: A technology for farming fish in tanks where water is filtered and recirculated, minimizing water usage and waste discharge.
• Biofilter Function: Core component of RAS that hosts beneficial bacteria for biological filtration and waste treatment.
• Nitrification Process: Two-step bacterial process where Nitrosomonas bacteria convert ammonia (NH₃) to nitrite (NO₂⁻), then Nitrobacter bacteria convert nitrite to nitrate (NO₃⁻).
• Waste Removal: Biofilters remove solid wastes including uneaten feed, fish feces, and other organic matter through bacterial decomposition.
• Phosphorus Management: Controlled through fish feed formulation, mechanical filtration, and water exchange, not through biofilters.
• Benefits of RAS: Water conservation, reduced environmental impact, disease control, and intensive fish production in limited space.