Effects of different biofloc sizes on the short‐term stress of Japanese seabass, Lateolabrax japonicus (Cuvier), juveniles reared in biofloc aquaculture systems

Abstract

Biofloc technology (BFT) is a new approach widely studied and applied in aquaculture (Avnimelech, 2012). In BFT systems, the bacterial communities involved in water treatment processes are stimulated to grow in suspension and form flocs through flocculation mechanisms. The major role of flocs in aquaculture is their ability to treat aquaculture water for continual use over several production cycles (Avnimelech, 2012;Kim et al., 2020), as natural food and probiotics (Avnimelech, 2012). BFT systems can also be associated with the set-up of recirculating aquaculture systems (RAS) and are often applied in the treatment of wastewater (Liu et al., 2021).However, when the C/N ratios in BFT are elevated in the aquaculture system, they not only maintain and enhance growth, including the population of microorganisms involved in heterotrophic assimilation and conversion of ammonia nitrogen into bacterial biomass, but also create problems, such as the rapid growth of flocs and total suspended solids (TSS) (Avnimelech, 2012;Hargreaves, 2006). In the BFT, high TSS levels can simultaneously increase the difficulty of controlling parameters such as dissolved oxygen (DO) (Avnimelech, 2012;Hargreaves, 2006) and exert biological effects of chronic stress on aquatic animals, thus affecting the stable operation and