High Doses of Norfloxacin Nicotinate Induce Apoptosis, Developmental Neurotoxicity, and Aberrant DNA Methylation in Zebrafish (Danio rerio) Larvae
by
Hansun Fang
1,2, 
Runping Wang
2,
Fang Wang
3,
Kaibin Li
3,
Huili Liang
3,
Tian Su
4,
Lili Wei
2,
Jiming Ruan
2,
Fugui Li
2,* and
Ximei Liang
2,* 1
Key Laboratory of Poyang Lake Basin Agricultural Resource and Ecology of Jiangxi Province, College of Land Resource and Environment, Jiangxi Agricultural University, Nanchang 330045, China
2
College of Animal Science and Technology, Jiangxi Agricultural University, Nanchang 330045, China
3
Pearl River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510380, China
4
Jiangxi Center Station of Irrigation Experiment, Nanchang 330201, China
*
Authors to whom correspondence should be addressed.
Animals 2026, 16(1), 18; https://doi.org/10.3390/ani16010018
Submission received: 3 November 2025
/
Revised: 16 December 2025
/
Accepted: 18 December 2025
/
Published: 20 December 2025
(This article belongs to the Section Aquatic Animals)
Simple Summary
Norfloxacin nicotinate (NOR-N), a derivative and effective substitute of norfloxacin (NOR), has been widely used in livestock production and aquaculture sectors. However, the adverse impacts of NOR-N on non-target animals and their associated biological response mechanisms are still not completely elucidated. This study revealed that exposure to the high doses of NOR-N induced apoptosis, developmental neurotoxicity and aberrant DNA methylation in zebrafish (Danio rerio) larvae. These findings contribute to uncovering the response mechanisms of fish to NOR-N exposure and enhancing understanding of the potential hazards that NOR-N may pose to aquaculture ecosystems.
Abstract
This study aimed to evaluate the response mechanisms of zebrafish larvae to Norfloxacin nicotinate (NOR-N) exposure. Embryos were exposed to NOR-N from 4 h post-fertilization (hpf) until 96 hpf. The exposure concentrations included 0.002, 0.2, 1, and 5 mg/L (simulating both normal and exceptionally high environmentally relevant levels of NOR), as well as a high dose of 25 mg/L. Subsequent analyses focused on apoptosis, neurodevelopment, and DNA methylation in the resulting zebrafish larvae. The results showed that high-dose NOR-N (≥5 mg/L) induced obvious apoptotic cell death in zebrafish larvae, accompanied by increased activities of Cas3 and Cas9, up-regulated P53, Bax, Puma, Apaf1, Cas3 and Cas9 genes expression, and reduced Mdm2 levels and Bcl2/Bax ratio. Moreover, exposure to 5 and/or 25 mg/L NOR-N resulted in a significant up-regulation of neurodevelopment-related genes (Sox2, Sox3 and Sox19a), concomitantly with a marked decline in the transcription of DNA methylation genes, including Dnmt1, Dnmt3a1, Dnmt3b1, Dnmt3b2 and Dnmt3b4. Overall, our findings demonstrated that NOR-N exposure could induce apoptosis, developmental neurotoxicity and aberrant DNA methylation in zebrafish larvae. These findings provide insights to guide the safe application of NOR-N in aquaculture and support the assessment of its potential ecological risks to aquatic ecosystems.
