Effects of ozone and oxygen nanobubbles on water quality, fish pathogens, and early life stages of rainbow trout (Oncorhynchus mykiss)

Nanobubble technology has recently been applied in various aquaculture systems. However, its application in seed production remains understudied. This study evaluates the effects of ozone nanobubbles (O₃NB) during the embryonic stage and oxygen nanobubbles (O₂NB) during the fry stage in rainbow trout ( Oncorhynchus mykiss ). Fertilized eggs at stage pigmented eyes were treated daily with O 3 NB at concentrations of 0.22 ± 0.02 – 0.23 ± 0.02 mg/L for 1 h (T1), 2 h (T2), and 3 h (T3), along with a non-treated control group. Each group was replicated three times. Hydrochemical parameters, including temperature, pH, Dissolved Oxygen (DO), Oxidation-Reduction Potential (ORP), ozone (O 3 ), N-NH 4 , H 2 S, N-NO 2 , Chemical Oxygen Demand (COD), and P-PO 4 3- , as well as pathogenic agents (fungi), embryo morphology, and histopathology were monitored daily. The results showed that water quality in groups T1, T2, and T3 differed significantly from the control group, with higher ORP values and lower levels of COD, N-NH₄, and total heterotrophic bacterial count (p < 0.05). The infection rate of Saprolegnia spp. in T1, T2, and T3 (0.89 ± 0.8 %, 0.33 ± 0.7 %, and 0.78 ± 0.4 %, respectively) was significantly lower compared to the control group (5.44 ± 1.9 %) (p < 0.05). The larval deformity rate in T1 (0.87 ± 0.11 %) was lower than in T3 (1.63 ± 0.25 %) (p < 0.05). Our study recommends that treatment with ozone nanobubbles (0.23 - 0.23 mg/L for 1 h) during embryogenesis, combined with maintaining dissolved oxygen at 10 mg/L using oxygen nanobubbles post-hatching, effectively reduces pathogen infections and enhances survival in rainbow trout. • Ozone nanobubbles (0.22–0.23 mg/L, 1 h) had no harm on rainbow trout embryos. • Ozone nanobubbles reduced Saprolegnia spp infections during the embryo stage. • Ozone nanobubbles (0.22–0.23 mg/L, 1 h) and oxy nanobubbles (10.26 – 10.38 mg/L) treatment raised hatching rate to 90.12 %.