Biotechnology and Bioinformatics (1+1)

6.3.2.3. Applications in fish farming

· Azolla is useful in aquaculture practices primarily as a nitrogenous biofertilizer.

· Its high decomposition rates also make it a suitable substrate for enriching the detritus food chain or for microbial processing such as composting prior to application in ponds.

· Further, Azolla can serve as an ingredient of supplementary feeds and as forage for grass carp too.

· Studies made on Azolla biofertilization have shown that the nutrient requirements of composite carp culture could be met through application of Azolla alone at the rate of 40t/ha/yr providing over 100 kg of nitrogen, 25 kg of phosphorus and 90 kg of potassium in addition to about 1500 kg of organic matter. This amounts to total substitution of chemical fertilizers along with environmental upkeep through organic manuring.

· It is observed that about 1 ton of Azolla biomass could be harvested every week from a water spread area of 650m², with a phosphorus input-nitrogen output ratio of 1:4.80.

· With an approximate water to land ratio of 1 : 0.5 the total land requirement of such an Azolla farm is 0.1 ha. For fertilizing 1ha of water area at the above suggested rate of 40t/ha/yr, about 550m² of water spread is required (1.5kg/m²/week; 42t/yr) with the total area of 800m², accounting for 6% if the area to be fertilized.

· Larger production plots (20m x 5m) could be provided reducing the total land area required for mass cultivation. There would however be regional variations depending on the agro-climatic conditions, as some species of Azolla give poor yields during low temperatures in winter.

Azolla is a new aquaculture input with high potentials in both fertilization and trophic enrichment. Studies are also being made with regard to reduction of land requirement and production costs through in situ cultivation in shallow zones or floating platforms in fish ponds, use of organic inputs like biogas slurry, etc. The costs may be reduced further if the Azolla culture system is managed by the farmer or by his household members. The technology would pave the way for economic, eco-friendly and environment – conserving fertilization in aquaculture.

The suggested application rate of Azolla to meet the nutrient requirements in carp polyculture (and substitute for chemical nitrogenous fertilizer) is 40 tons/ha/year. This requires an area of about 800 sq m, a unit that could be taken up as a subsidiary farming activity. Along with the environmental benefits, a saving of up to 30-35% over the traditional manuring practices is estimated.