Updated: Oct 4
One of the major quality problem in intensive aquaculture Is the accumulation of nitrogen species(NH4+, and NO2 -) in water and the sources are -
a. Excreta of animals and its deposition
b. Protein-rich feed which is needed for the growth and development of animals, because the energy production pathway depends, to a large extent, on the oxidation and catabolism of protein.
In highly aerated ponds, ammonia is oxidized to NO2- by bacteria and ultimately forms NO3-.
Generated CO2 is released to the air by diffusion or forced aeration. But there is no effective mechanism to release the nitrogenous metabolites out of the pond. Hence the water body is getting enriched with ammonia and other inorganic nitrogenous species.
This problem can be sorted out by frequent water exchange but has got the limitations (3 limitations mainly).
1. Environmental regulation prohibits the release of nutrient-rich water into the environment.
2. The danger of introducing pathogenic bacteria
3. The high expense of pumping water
Apart from that, the frequent water exchange may cause the temperature shock to the animals and the animals may go under stress due to such frequent change of environment.
The other approach is to encourage and enhance nitrification of ammonia to nitrite to nitrate by employing BIOFILTERS ( Large surface service area with immobilized nitrifying biomass in a controlled environment). Again it has the limitations,
1. High-cost involvement and high preparation period for a stabilized system.
2. Needs to target and digest a large mass of feed residue( almost 50% of the feed)
The other strategy that has got the attention is the removal of ammonia from water through its assimilation into microbial protein by addition of carbonaceous material into the system.
The advantage of this approach is that….it provides a potential source for fish/prawn and maybe a potential substitute of external feed.