What are Recirculating aquaculture systems (RAS)?

Recirculating aquaculture systems (RAS) are unique engineered ecosystems that minimize environmental perturbation by reducing nutrient pollution discharge. They are indoor, tank-based systems in which fish are grown at high density under controlled environmental conditions.

What is the main benefit of Recirculating aquaculture systems (RAS)?

The main benefit of RAS is the ability to reduce the need for fresh, clean water while still maintaining a healthy environment for fish.

What is biofiltration in Recirculating aquaculture systems (RAS)?

All Recirculating aquaculture systems (RAS) relies on biofiltration to convert ammonia excreted by the fish into nitrate. Ammonia is a waste product of fish metabolism and high concentrations (>.02 mg/L) are toxic to most finfish.

Thus, a biofilter system purify the water and remove or detoxify harmful waste products and uneaten feed. Biofilters use microorganisms, which are capable of degrading many compounds, fixed to an inorganic/organic medium to break down pollutants present.

Ammonia is removed from an aquarium system through the use of a biofilter. The biofilter provides a substrate on which nitrifying bacteria grow. These nitrifying bacteria consume ammonia and produce nitrite, which is also toxic to fish. Other nitrifying bacteria in the biofilter consume nitrite and produce nitrate.

Biofilters are also used to remove phosphorus waste by-products generated by fish.

What are the advantages of Recirculating aquaculture systems (RAS)?

Reduced water requirements as compared to raceway or pond aquaculture systems.

Reduced land needs due to the high stocking density.

Site selection flexibility and independence from a large, clean water source.

Reduction in wastewater effluent volume.

Increased biosecurity and ease in treating disease outbreaks.

Ability to closely monitor and control environmental conditions to maximize production efficiency.

Similarly, independence from weather and variable environmental conditions.

What are the disadvantages of Recirculating aquaculture systems (RAS)?

High upfront investment in materials and infrastructure.

High operating costs mostly due to electricity, and system maintenance.

A need for highly trained staff to monitor and operate the system.

Higher greenhouse gas emissions than non-recirculating aquaculture

PRACTICE QUESTIONS

QUES . With reference to the role of biofilters in Recirculating Aquaculture System, consider the following statements: UPSC PRELIMS 2023

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?

(a) Only one

(b) Only two

(c) All three

(d) None

Show Answer