WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2024 47 (CONTINUED ON PAGE 48) of nitrate and total suspended solids are factors that influence the performance of macroalgae, demanding the establishment of limit concentrations. Using proportions of 100%, 75%, 50%, 25%, and 0% of a biofloc inoculum from an operational system generated concentrations of 0, 100, 200, 250, and 300 mg L-¹ of total suspended solids and 0, 28, 45, 56, and 73 mg L-¹ of nitrate. Although diluting the biofloc inoculum reduced the concentration of total suspended solids, it also diluted the concentration of nutrients, which became a limiting factor for macroalgae growth. The treatments with 250 and 300 mg L-¹ of total suspended solids achieved the best nitrate removal rates from the system, with values of 55% and 38%, respectively. However, only the treatment with 250 mg L-¹ of solids showed a phosphate removal rate of 31%. This result is associated with a better balance of nitrogen and phosphorus at the start of cultivation, with a lower concentration of solids compared to the 100% inoculum treatment. In the tanks where no inoculum was added, ammonia concentrations should have increased due to leaching from the shrimp feed and excretion, requiring the use of organic carbon for bacterial growth in the system (Krummenauer et al. 2011). However, there was no increase in ammonia concentrations, probably due to absorption by the macroalgae, as ammonia is the macroalgae’s primary nitrogenous compound and is rapidly assimilated from the system without much energy input (Castelar et al. 2014). Different nutrient availability, the predominance of a nitrogenous compound, and the concentration of solids not only influence the algae’s growth and rate of nutrient absorption but also modify their proximal composition and bioactive compounds (Duke et al. 1989). A higher protein and lower ash content was found in the macroalgae produced in biofloc with 250 mg L-¹, as well as a higher concentration of chlorophyll-a, compared to the control treatment (0% inoculum). These results show that the greater availability of nitrate in the system, despite not being the macroalgae’s preferred compound, is still utilized in the tissue. With the increase in protein content, having an indirectly proportional relationship, there was a decrease in the ash content of the macroalgae cultivated in biofloc, improving their nutritional value (Queirós et al. 2021). The increase in chlorophyll was due to the macroalgae’s need to increase pigments to maximize light absorption, which was affected by the high turbidity of the biofloc system (Levavasseur 1989) (Table 2). As a result, better nutrient absorption and increases in protein and pigments are found in macroalgae cultivated in an integrated system with shrimp and biofloc with initial solids levels of 250 mg L-¹. Effect of Organic and Inorganic Fertilization Different fertilization methods to initiate cultivation in a biofloc system will favor the growth of specific groups of bacteria, affecting water quality parameters, production costs, and the performance of the organisms. Chemical fertilization in the system promotes the growth of chemoautotrophic bacteria, which oxidize ammonia to nitrite and then to nitrate, which eventually accumulates in the cultivation cycle (Ferreira et al. 2021). This system is characterized by a high concentration of nitrate, low production of total suspended solids, and greater consumption of alkalinity by the bacteria. At the beginning of cultivation, chemical fertilizers are used to encourage bacterial growth, and inorganic carbon is used to increase the alkalinity that will be consumed in the nitrogen oxidation process. The establishment of bacteria in this system is slower, taking between 30 and 45 days with the use of an artificial substrate to fix the bacteria (Ferreira et al. 2021). For organic fertilization, the process involves adding organic carbon from products such as molasses and dextrose, among others (Ebeling et al. 2006). This fertilization favors the growth of heterotrophic bacteria, which establish themselves in the system more TABLE 2. Proximal composition and biocompounds of the macroalgae (dry matter) at the end of cultivation in the CONT (cultivation in clear water) and T250 (use of 75% biofloc inoculum, a concentration of approximately 250 mg L-1 of total suspended solids) treatments. TREATMENTS Proximal Composition CONT T250 Moisture (%) # 77.42 ± 0.09 b 75.50 ± 0.23 a Protein content (%) 22.85 ± 0.37 b 24.26 ± 0.89 a Lipids (%) 0.53 ± 0.19 0.48 ± 0.19 Ash (%) 30.17 ± 1.80 b 28.30 ± 0.64 a Fiber (%) 10.65 ± 0.78 11.59 ± 3.41 Non-nitrogenous extract (%) 35.77 ± 1.30 35.58 ± 1.44 Biochemical Analysis CONT T250 Protein (%) 23.30 ± 1.59 25.85 ± 2.81 DPPH (%) 90.31± 5.38 92.97 ± 5.80 Chlorophyll-a (mg g -1) 2.18 ± 0.03 b 2.27 ± 0.03 a Chlorophyll-b (mg g -1) 2.99 ± 0.28 3.31 ± 0.10 Carotenoids (mg g -1) 0.19 ± 0.10 0.10 ± 0.03 Total Polyphenols (mg GAE g -1) 0.38 ± 0.12 0.33 ± 0.09 # humid matter. Different letters represent significant differences (p ≤ 0.05) between treatments after Student’s t-test.
RkJQdWJsaXNoZXIy MjExNDY=