Bioflocs-assisted mass culture of Brachionus plicatilis under prolonged zero-water exchange and its application to Pagrus major larviculture

The sustainable mass production of rotifers is crucial to sufficiently supply marine fish hatcheries. However, maintaining a stable rotifer culture is still a challenge mainly due to unionized ammonia (NH 3 ) toxicity and biological contaminants. This study investigated the effectiveness of single initial inoculation of bioflocs (BF) in addressing the abovementioned problems on rotifer mass culture using Brachionus plicatilis subjected to three treatments for 29 days, namely: 1) water exchange (WE), 2) zero water exchange (ZE), and 3) bioflocs × zero water exchange (BF × ZE). The effects of feeding BF-cultured B. plicatilis and supplementing BF in the rearing water on the survival and growth of red sea bream Pagrus major larvae for 14 days were evaluated. Bacterial composition of BF was determined. BF inoculation resulted in significantly higher rotifer densities from day 14 to day 29 (BF × ZE with 226–434 individuals/mL vs WE and ZE with 69–131 individuals/mL). BF inoculation significantly controlled ciliate contamination (BF × ZE with 7–25 ciliates/mL vs ZE with 421–531 ciliates/mL) from day 21 to day 25. TAN and NH 3 concentrations were significantly reduced in the BF × ZE than in ZE and WE treatments on day 29. P. major larvae fed BF-cultured rotifers and reared in BF-supplemented water did not show reduced survival and growth. BF inoculation significantly improves B. plicatilis productivity through the effective removal of NH 3 via the ammonia-oxidizing activity of Nitrosomonas nitrosa and bacteria within the phylum Chloroflexota under prolonged zero-water exchange conditions. Furthermore, the study demonstrates the viability of BF in P. major larviculture. • Bioflocs enhance rotifer production under prolonged zero-water exchange. • Bioflocs-associated bacteria regulate TAN and NH 3 in rotifer mass culture. • Bioflocs control ciliate contamination in rotifer mass culture. • Bioflocs-cultured rotifers in Pagrus major larviculture.