Ozone nanobubble effects on early development of rainbow trout (Oncorhynchus mykiss) and rearing-water microbial communities in a flow-through hatchery

Nanobubble technology is increasingly being explored in aquaculture for its potential to enhance water quality, control pathogens, and improve fish performance. This study investigated the effects of ozone nanobubbles (O 3 NB) on rearing-water microbial communities and early development of rainbow trout ( Oncorhynchus mykiss ) in a pond-water-sourced flow-through hatchery system. A two-factorial experimental design combined four O 3 NB water treatments (Control; Low: 277 ± 104 mV; Moderate: 392 ± 134 mV; High: 610 ± 122 mV) with two rearing techniques (with or without regular removal of unfertilised eggs and dead individuals; R and NR). O 3 NB exposure altered microbial community composition in rearing water, with alpha-diversity indices (ACE, OTU, Shannon, Simpson) showing negative relationships with increasing O 3 NB intensity. Taxonomic profiling indicated a marked reduction in genus richness under higher O 3 NB exposure, with communities dominated by Moheibacter, Tepidimonas , and Sphingobacterium . Regular removal of dead organic matter increased hatching and survival compared with non-removal. O 3 NB effects were dose-dependent: the highest mean larval body length and high hatching success (∼80%) occurred under Low O 3 NB treatment among surviving larvae, particularly under R-technique, while Moderate and High exposures reduced hatching (