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

Abstract

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 (O₃NB) 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 O₃NB 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). O₃NB exposure altered microbial community composition in rearing water, with alpha-diversity indices (ACE, OTU, Shannon, Simpson) showing negative relationships with increasing O₃NB intensity. Taxonomic profiling indicated a marked reduction in genus richness under higher O₃NB exposure, with communities dominated by Moheibacter, Tepidimonas, and Sphingobacterium. Regular removal of dead organic matter increased hatching and survival compared with non-removal. O₃NB effects were dose-dependent: the highest mean larval body length and high hatching success (∼80 %) occurred under Low O₃NB treatment among surviving larvae, particularly under R-technique, while Moderate and High exposures reduced hatching (<40 %) and survival (<5 % in High-NR). Yolk-sac absorption occurred more rapidly under O₃NB exposure, but was completed across all groups by 77 dpF. Overall, these findings indicate that low-level O₃NB, when used to complement (rather than replace) standard hatchery practices such as the removal of dead organic matter, can support microbial control and early developmental performance of rainbow trout in hatchery systems with elevated organic load. In contrast, excessive exposure compromises embryo viability and larval survival. Further optimisation of O₃NB dosing and application strategies is therefore required, recognising the effectiveness and safety under different system-specific conditions.