58 MARCH 2024 • WORLD AQUACULTURE • WWW.WAS.ORG effect on growth, feed conversion, haematological indicators and biochemical parameters of fish. Azolla is often referred to as a “super plant” due to its high productivity and nitrogen fixing characteristics, and its potential as a dietary nitrogen source for fish. Dietary Azolla positively affects growth, feed utilization, and intestinal endogenous enzymes as well as improves haematobiochemical parameters, oxidative responses, and flesh quality of fish (Figure 4). Azolla may also show a synergistic benefit in fish upon the addition of probiotics to their diet. The incorporation of Azolla in fish diets lowers their cost, and the use of cheaper feed ingredients helps to achieve higher profit margins to the farmers. In cage culture of Nile tilapia, a farmer may improve net revenue by 22 percent through the replacement of 25 percent commercially available formulated feed with Azolla (Mansour et al. 2023). Challenges for Azolla Use in Aquafeed Plant cells can contain high amounts of fibers and starch, and diets with amounts of fiber are generally indigestible for carnivorous fish species due to the absence of cell-wall breaking enzymes in these fish. Additionally, anti-nutritional factors (ANFs) like protease inhibitors, phenolic compounds, phytates, lectins, and oligosaccharides exist in high amounts in plant-based protein sources, and these should be neutralized before incorporating them into aquafeed (Yohana et al. 2023). For instance, the presence of ANFs in soybeans can induce an inflammatory response and cytosolic enzyme activities, which adversely affect disease resistance in fish. While ANFs of plants negatively affect the health of farmed fish by interfering with nutritional metabolism, many plant-based ingredients can be used in aquaculture feed by minimizing these ANFs. ANF Reduction Techniques for Azolla Thermal processing and chemical processing are two methods for lowering ANFs in plant-based feed ingredients. Thermal treatments improve the feed’s nutrient availability, and fish digestion, by changing its chemical structure. Cooking, toasting, steaming and extrusion are heat-treated techniques that deactivate these dangerous compounds. For example, extrusion can denature lectins, which restrict carbohydrate absorption, and boiling can diminish trypsin inhibitors, which suppress protein digestion in soybeans. ANFs are also inactivated by certain chemical treatments Nutrient Profiling Azolla is an ultimate source of feed for livestock and fish and can be used as an alternative source of artificial feed and fodder to improve the production of farm animals. Azolla has 20-30 percent protein content, 10-15 percent mineral content, and 7-10 percent amino acids on a dry weight basis (Table 2). Application of Azolla in Aquaculture Azolla can be used either as fresh feed or mixed in dried condition with other feed ingredients for aquafeeds. Azolla feed can be prepared either solely using plant-based protein sources without adding fishmeal or when partially adding fishmeal. Azolla should be incorporated into the diet of cultured fish as recommended in Table 3. Relating to the high nutrient composition of Azolla, even the fry and fingerling stages of many fish perform extremely well in terms of growth and survival when consuming Azolla-based diets. Consumption of Azolla improves fish disease resistance, resulting increased survival. High levels of essential amino acids, vitamins, minerals, and carotenoids in Azolla help in the improvement of the immune and digestive systems. However, phenol content, carotenoids, flavonoids, and tannins of Azolla are also linked to increasing antioxidant and immunostimulant functions. For example, the consumption of dietary Azolla by Nile tilapia has been shown to enhance resistance to Streptococcus agalactiae infection due to improvements in the active immune system. If the harvested Azolla is directly used for feeding fish (Figure 3), the total quantity of Azolla should be given as 10 percent of fish biomass. Therefore, the area of Azolla production depends on the method of Azolla applied for fish feeding. For Example, if 10,000 fingerlings averaging 10 grams each are stocked in a pond, the total biomass of fish = (10000*10 gm)/1000 = 100 kg, and the daily requirement of fresh Azolla is 100*10/100= 10 kg at the time of stocking. The area of Azolla production required is at least 15-20 m2 at the time of stocking. Effects of the Azolla in the Diet of Fish Azolla can be used to formulate an eco-friendly and costeffective feed for mass production of fish through intensification. Azolla can be a good replacement for high cost animal protein for fish at levels of 10-50 percent incorporation without any adverse FIGURE 3. Feeding of fresh Azolla in aquaculture pond FIGURE 4. Effects of Azolla feed on cultured fish
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