Improvement of biofloc quality and growth of Macrobrachium rosenbergii in biofloc systems by Chlorella addition

This research aimed to elucidate the effect of Chlorella sp. addition on biofloc quality and growth of Macrobrachium rosenbergii juveniles in biofloc systems. Four treatments of freshwater prawn nursery culture systems were tested, i.e., control system with clear water system at a regular water exchange at about 50% every 2 weeks; control system with Chlorella sp. addition with regular water exchange and weekly addition of Chlorella sp.; biofloc system without Chlorella sp. addition; and biofloc system with Chlorella sp. addition. Freshwater prawn juvenile at an average initial body weight of 0.25 g was randomly distributed into 16 units of aquarium with a working volume of 100 L at a density of 20 prawn/aquarium (50 prawn/m 2 ). Molasses was added every day into biofloc treatments at an estimated C/N ratio of 6.25. Chlorella sp. was added into the microalgae treatments at the initiation of the experiment and every 2 weeks at 10% of the total volume to reach an estimated final density of about 10 5 /mL. Microbial aggregation was inhibited by vanillin (a quorum sensing inhibitor) addition regardless the presence of Chlorella sp. The microalgae addition resulted in biofloc with higher density, larger particle size, and higher protein content. Different amino acid and fatty acid profiles of biofloc were observed between the biofloc treatments. Essential amino acid index of biofloc with the addition of Chlorella sp. was about 39% higher compared to that of biofloc without Chlorella sp. addition. The growth of freshwater prawn in biofloc systems was generally higher than those of the control with and without Chlorella sp. addition. In conclusion, the addition of Chlorella sp. could improve biofloc quality and the growth performance of freshwater prawn juveniles.