Blue-violet light (405 nm): a non-chemical intervention for Metanophrys sp. infection in large yellow croaker (Larimichthys crocea)
摘要
Scuticociliatosis inflicts substantial economic losses on the large yellow croaker (Larimichthys crocea, LYC) farming industry in China. To explore the efficacy of blue-violet light in controlling scuticociliatosis in LYC, Metanophrys sp. (3 × 104 ciliates) were exposed to 365 nm, 405 nm, and 465 nm light-emitting diode (LED). The mortality rate and morphological changes of the ciliates were monitored to identify the most effective wavelengths. Furthermore, in vivo treatment experiments were performed to evaluate the therapeutic effects of 365 and 405 nm LED light against scuticociliatosis, following experimental infection of LYC with Metanophrys sp. A safety assessment of LED illumination on the fish was also conducted alongside the efficacy trials. Results showed that exposure to 365 nm light for 80 min (10.9 J/cm2) or to 405 nm light for 120 min (125.1 J/cm2) induced 100% mortality of Metanophrys sp. Under irradiation at these wavelengths, the ciliates underwent a sequential series of morphological alterations: they first transformed from an oval to a spherical shape, followed by ciliary detachment, and ultimately cellular rupture. In contrast, 465 nm light exerted only a negligible effect on the parasites, resulting in a mere 2% mortality rate with no observable morphological changes. In the in vivo trial, the survival rate of Metanophrys sp.-infected LYC exposed to 405 nm LED light reached 76.7%—a value that was not significantly different from that of the healthy control group (90.0%) but markedly higher than those of the infected-untreated group (35.7%). The safety assessment revealed that exposure to 405 nm light for 14 days caused reversible changes in ocular melanin levels in LYC, whereas exposure to 28 days resulted in a significant decrease in survival rate and more severe eye damage. In conclusion, 405 nm blue-violet light safely and effectively controlled Metanophrys sp. infection in LYC. This finding validates its potential as an eco‑friendly non-chemical intervention for the managing of parasitic ciliate diseases, offering a practical and sustainable solution particularly suited to intensive aquaculture systems.
Graphical Abstract