WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2024 49 Applying the Biomass Produced Macroalgae have significant economic value, particularly in the pharmaceutical, food, and cosmetics industries (Almeida 2013). Their applicability is extensive, ranging from the use of fresh or dried biomass to obtaining by-products such as polysaccharides and pigments (Siddik et al. 2023). To obtain macroalgae with the best nutritional value, the type of cultivation system and management methods must be taken into consideration. It was found that macroalgae cultivated in biofloc had their protein content doubled (24%) compared to cultivation with laboratory solution (12%) (Carvalho et al. 2023), along with a decrease in ash and an increase in the concentration of pigments. Therefore, producing macroalgae biomass with high nutritional content represents a high-quality product that can be reintegrated into the production system. The transformation of waste into resources aligns with the “Circular Economy” concept, where resources produced in the system are reused multiple times in a closed circuit (Cornejo-Ponce et al. 2020). Instead of disposing of waste, materials and products are reused, recycled, and recovered (Velenturf and Purnell 2021). As a result, due to their nutritional characteristics, macroalgae of the genus Ulva have begun to be used as additives or substitutes for some ingredients in shrimp and fish feed (García-Vaquero 2018) ruminants (small and large animals. Marinho et al. (2013) tested inclusions of 10%, 15%, and 20% macroalgae meal in tilapia diets and found that diets with up to 10% macroalgae inclusion are feasible without affecting species performance. Consequently, to utilize the macroalgae biomass produced in previous experiments in an integrated system with biofloc, four isoprotein (41%) and isolipid (8.0%) diets were prepared for this experiment, with different levels of macroalgae inclusion in the diet (Table 3). In the control treatment, no macroalgae were added (T0), then 5.0% macroalgae were added to one diet (T5), 10% macroalgae were added (T10), and 15% macroalgae were added (T15). The results show that the addition of macroalgae to the diet did not affect the tilapia’s performance (Table 4, Figure 4). More studies need to be conducted to assess the antioxidant and physiological effects of macroalgae on fish, given that macroalgae contain (CONTINUED ON PAGE 50) TABLE 3. Ingredient composition and proximate analysis of experimental diets (% dry matter) containing U. lactuca meal at different levels. EXPERIMENTAL DIETS Ingredients (%) T0 T5 T10 T15 Fish meal 40.00 40.00 40.00 40.00 Soybean meal 33.00 32.00 31.00 30.00 Wheat bran 12.00 8.00 4.00 0.00 Gelatin 2.00 2.00 2.00 2.00 Soy oil 2.00 2.00 2.00 2.00 Fish oil 2.00 2.00 2.00 2.00 Cellulose 4.00 4.00 4.00 4.00 Vitamin/ mineral mix 5.00 5.00 5.00 5.00 Ulva meal 0.00 5.00 10.00 15.00 Proximal composition (%) T0 T5 T10 T15 Feed crude protein 42.44 41.82 41.37 39.98 Feed crude fat 8.23 8.07 8.05 8.64 Feed ash 16.28 17.45 19.01 20.02 TABLE 4. Tilapia performance in treatments T0 (no macroalgae included), T5 (5% macroalgae included in the diet), T10 (10% macroalgae included in the diet) and T15 (15% macroalgae included in the diet) during 42 days of cultivation. TREATMENT Parameters T0 T5 T10 T15 Final average weight (g) 10.78 ± 0.51 11.44 ± 0.84 10.35 ± 0.92 10.33 ± 0.15 WWG (g week-1) 1.64 ± 0.09 1.75 ± 0.14 1.57 ± 0.15 1.56 ± 0.35 SGR (% dia-1) 5.82 ± 0.11 5.95 ± 0.15 5.71 ± 0.20 5.70 ± 0.40 FCR 1.00 ± 0.07 0.96 ± 0.09 0.99 ± 0.06 1.02 ± 0.02 Survival (%) 87.50 ± 15.00 85.00 ± 5.77 95.0± 5.77 90.00 ± 0.00 WWG weekly weight gain; SGR specific growth rate; FCR feed conversion rate.
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