Correct Option (B)
Recirculating Aquaculture Systems (RAS) utilize bio-filters as a critical component for maintaining water quality. Their primary function involves biological treatment of waste products generated by aquatic organisms.
- Statement 1 is correct: Bio-filters contribute to the overall waste treatment process in RAS. While mechanical filtration systems are primarily responsible for removing solid waste like uneaten fish feed and fecal matter, bio-filters break down dissolved organic compounds originating from these wastes. This biological degradation reduces the organic load in the water, thereby contributing to the removal of components derived from uneaten feed.
- Statement 2 is correct: This is a fundamental role of bio-filters. They facilitate the nitrification process, where specialized nitrifying bacteria (e.g., Nitrosomonas and Nitrobacter) convert highly toxic ammonia (NH₃), produced from fish excretion and decaying organic matter, first into nitrite (NO₂⁻) and then into significantly less toxic nitrate (NO₃⁻). This conversion is essential for fish health and survival in a closed system.
Incorrect Options
- Statement 3 is incorrect: Bio-filters do not increase phosphorus levels in the water. Their primary function is nitrogenous waste removal. Phosphorus is a key nutrient, but its accumulation can lead to eutrophication and algal blooms, degrading water quality. Managing phosphorus levels in RAS typically involves feed management, sludge removal, and sometimes specific phosphorus removal technologies, not bio-filtration.
- Options (1), (3), and (4) are incorrect because only two of the given statements (1 and 2) are factually accurate.