It is generally known that fermentation of cereal brans improves their numtrient value, in particular through increasing protein content (e.g., Hassan et al., 2008; Silveira & Badiale-Furlong, 2009). In the field experiments described below, we have tested the attractiveness of fermented and unfermented white brans for cyprinid fish.

Wheat bran for human consumption was fermented with 0,2 % of dry baker yeast (Saccharomyces cerevisiae). Fermentation of moistured bran was carried out at 25^o C within 2 days in plastic bags with the leaking lids.

Moist fermented and moistured unfermented brans were mixed with the pure dry grey clay in proportion 1:1 or 1:2, depending on the clay quality. Both mixes were rolled into the balls (3 cm diameter) and dried in air within 12 hours. Then dry balls (that had practically the same color) were strung on the lines ended by the small button like stoppers, with marks to distinguish them.

In the field, lines with the two compared balls were tied (25 cm between centers of the balls) to the cross bar placed above the water with the help of two racks. Narrow channels (40-50 cm width) in the shallows between macrophytes (usually water lily, Nuphar lutea, and pondweeds Potamogeton spp.) were selected. Balls went down to the depth of about 5 cm, to attract roach and other top dwelling fish, or about 30 cm, to attract crucian and other bottom dwelling fish.

In the surface tests, mainly juvenile roach, Rutilus rutilus, rudd, Scardinius erythropthalmus, as well as juvenile and adult river bleak, Alburnus alburnus, were attracted. In lentic waters, lake bleak, Leucaspius delineatus, occured instead of river bleak. In the bottom tests, mainly juvenile crucian, Carassius carassius, tench, Tinca tinca, as well as juvenile and adult bitterling, Rhodeus amarus, (in areas with the sandy bottom) were attracted.

After immersion into the water, clay balls with fermented and unfermented wheat brans were beginning to crumble with bran particles and attract fish. The fish were biting and destroying the balls. So, the first touch of fish to one of the balls and the destruction of the most attractive ball first were used as criteria for statistical estimations.

The following results were obtained in the first session. Fish first touched 12 balls with the fermented wheat bran versus 3 balls with unfermented bran of 15 pairs of both kind balls offered (sign test, n = 15, z (+) =12, p < 0,05). Similarly, fish first destroyed 13 balls with the fermented bran (sign test, n = 15, z (+) =13, p < 0,01) showing in this way the attractiveness (both olfactory and gustatory) of fermented bran. The same preferences were observed in other four sessions.

Basic References

Hassan E.G., Award Alkareem A.M., Mustafa A.M.I. 2008. Effect of fermentation and particle size of wheat bran on the antinutritional factors and bread quality. Pakistan Journal of Nutrition 7, 521-526

Silveira C.M., Badiale-Furlong E. 2009. Sperathe effects of solid-state fermentation in the functional properties of defatted rice bran and wheat bran. Brazilian Archives of Boilogy and Technology 52, 1555-1562

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

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