Chemical analyses of 21 species of dried aquatic plants indicate that they contain the sufficient quantities of nutrients to be considered as livestock feedstuffs (Linn et al., 1975). Although considerable variations are among 21 species, 14 species contain more than 10% protein and all species contain less than 30% crude fiber. Mixed aquatic plant species (approximately 50% Myriopbyllus, 30% Ceratopbyllum, 10% Potamogeton, 5% Vallisneria and 5% unknown) have been ensiled with the organic acids (acetic, formic, propionic), corn or alfalfa. After 47 days of fermentation the silages have had pH values above 4.5 and lactic acid values below 0.4% of the dry matter. Acoording to Linn et al. (1975), acid-treated aquatic plant and alfalfa silages are higher in crude protein, indicating that acid additions decrease protein loss during fermentation.

To facilitate fish cultivation in rural areas of the Neotropics, the potential of cosmopolitan and locally available aquatic macrophytes from northern Colombia (Lemna minor, Spirodela polyrhiza, Azolla filiculoides and Eichhornia crassipes) as alternative fish feed are studied by Cruz et al. (2011). Considering the importance of fermentation in improving nutritional value of non-conventional feeds, fermentation properties and effects of anaerobic fermentation on the nutritional quality of the selected aquatic plants are evaluated. Although the fermentability coefficients (FC) of the selected aquatic macrophytes reveal hardly fermentable materials (FC < 35), the use of bacteria inoculants (Lactobacillus plantarum) and molasses (150 g kg^-1) results in good silage quality. Lactic acid fermentation positively affects the nutritional quality of the selected plants, reducing the concentration of some antinutritional substances (trypsin inhibitor, phytates, tannins and more) and crude fibre content.

According to Cruz et al. (2011), an amino acid profile of the raw macrophytes is sufficient to amino acid requirements of tropical fish Nile tilapia (Oreochromis niloticus) and pacu (Piaractus mesopotamicus). The amino acid profile is similar in the raw plants and represented by 5,30 to 6,28 g per 100 g protein in lysine and 1,72 to 2,04 g per 100 g protein in methionine. In addition, the tested aquatic macrophytes show to be rich in aspartic acid and glutamic acid. However, the effects of lactic acid fermentation on the protein content are conditional and strongly depend on the plant species. According to Cruz et al. (2011), the crude protein in fermented Azolla and Eichhornia decreases (due to slower acidification), but increases in fermented Lemna and Spirodela (maybe through an additional microbial synthesis).

Aquatic macrophytes such as Elodea nuttalli, Vallisneria natans, Alterranthera philoxerides that are widely distributed in water environments have been used as substrate of solid-state fermentation to produce crude protein extraction (Xiao et al., 2009). The experimental results show that the crude protein content of products with mixed strains fermentation is higher than that with single-strain fermentation. The crude protein content in V. natans fermented with the mold strain, Aspergillus niger, and yeast, Candida utilis, (taken in the ratio 1:1at 28^o C for 72 hours) is highest (39,88 %) among the fermented aquatic macrophytes examined in this study.

Among other inoculants to ferment aquatic and terrestrial plants, fish intestinal bacteria are widely used (e.g., Bairagi et al., 2004; Saha & Ray, 2011).

Molasses fermented, cow rumen content fermented and yeast fermented water hyacinth (E. crassipes) have been  incorporated into isonitrogenous and isocaloric test diets for fingerlings of Nile tilapia, O. niloticus, by El-Sayed Abdel-Fattah (2003). In final sum, diets with molasses fermented water hyacinth have been utilized more efficiently than diets with yeast fermented and cow rumen content fermented water hyacinth, respectively. According to Tham et al. (2013), addition of molasses and rice bran as an absorbent, but not an inoculant in the form of fermented vegetable juice (Brassica campestris), improve the quality of fermented water gyacinth as food.

Basic References

Bairagi A.., Sarkar Ghosh K., Sen S.K., Ray A.K. 2004. Evaluation of nutritive value of Leucaena leucocephala leaf meal inoculated with fish intestinal bacteria Bacillus subtilis and Bacillus circulans in formulated diets for rohu, Labeo rohita (Hamilton) fingerlings. Aquaculture Research, 35, 436-446.

Cruz Y., Kijora C., Wedler E., Danier J., Schulz C. 2011. Fermentation properties and nutritional quality of selected aquatic macrophytes as alternative fish feed in rural areas of the Neotropics. Livestock Research for Rural Development 23, article # 239

El-Sayed Abdel-Fattah M. 2003. Effects of fermentation methods on the nutritive value of water hyacinth for Nile tilapia Oreochromis niloticus (L.) fingerlings. Aquaculture 218: 471-478

Linn J.G., Staba E.J., Goodrich R.D., Meiske J.C., Otterby D.E. 1975. Nutritive value of dried or ensiled aquatic plants. I. Chemical composition. Journal of Animal Science 41, 601-609

Saha S., Ray A.K. 2011. Evaluation of nutritive value of water hyacinth (Eichhornia crassipes) leaf meal in compound diets for rohu, Labeo rohita (Hamilton, 1822) fingerlings after fermentation with two bacterial strains isolated from fish gut. Turkish Journal of Fisheries and Aquatic Sciences 11, 199-207

Tham H.T., Man N.V., Pauly T. 2013. Fermentation quality of ensiled water hyacinth (Eichhornia crassipes) as affected by additives. Asian-Australasian Journal of Animal Sciences 26, 195-201

Xiao L., Yang L., Zhanga Y., Gua Y., Jianga L., Qinb B. 2009. Solid state fermentation of aquatic macrophytes for crude protein extraction. Ecological Engeneering 35, 1668-1676