6 tropical and warm species (A. filiculoides, A. pinnata, etc.). The aquatic fern Azolla contains a symbiotic, heterocystous, blue-green alga, Anabaena azollae within cavities in its leaves. By the process of nitrogen-fixation the alga is capable of fulfilling the N requirements of the association.
An Azolla plant consists of a short, branched, floating stem, bearing roots which hang down in the water. Each leaf is bi-lobed, the upper lobe containing green chlorophyll while the lower lobe is colourless. Under certain conditions, an anthocyanin pigment, also occurs giving the fern a reddish-brown colour. This is particularly associated with over-fertilization of ponds, pollution and excess sunlight. Shaded conditions are preferred to full exposure to tropical sunlight.
The plant is highly productive with the ability to double its weight in 7 days. It can produce 9 tonnes of protein per hectare of pond per year. It is used as green manure (in rice paddies), stock feed and for controlling mosquitoes by blocking water-surface. Because the fern can form dense mats on water surfaces, it is classified as a water weed in many areas.
Azolla has reportedly been used as a feed for pigs and ducks in SE Asia; for cattle, fish and poultry in Vietnam; and for pigs in Singapore and Taiwan. It is described as an excellent substitute for green forage for cattle in Vietnam and may replace up to 50% of the rice bran used as feed for pigs in that country.
Although very low in DM, it contains a high level of protein (24% CP). The amino acid composition of Azolla compared well with reference protein sources. Methionine is low, as with many leaf proteins, but the value for lysine is more than twice that of corn.
As a supplement for growing pigs, performance was reduced compared to controls in the growing phase but the animals compensated and grew faster in the period from 24-89 kg. It has been used as a sole feed for lactating sows which have a higher intake to deal with the low DM content.
Ducks (650-1800g LW) consumed 350g Azolla when given free-choice with sugarcane juice and soya (about 5% of the diet). It is also used for grazing ducks and geese in paddy fields where the Azolla is used as a fertilizer.
As % of dry matter
Amino acid composition as % of crude protein
Azolla filiculoides Ref: 634