<p>Nitrite is a prevalent environmental contaminant in the natural water domain and poses a significant threat to fish populations due to its toxic effects. The aim of the study was to investigate the impact of nitrite concentration on cell apoptosis, oxidation reaction mechanism, and immune pathway of sea bass during simulated live transport. Fish were exposed to nitrite concentrations of 0, 15.05, and 30.11 mg/L for 48 h, respectively. Blood and liver samples were collected at intervals of 0, 12, 24, 36, 48, R12, and R24 h post-exposure to assess hematological parameters, oxidative stress indicators, immunological enzyme activities, and gene expression levels. The results indicated that the nitrite-exposed group had lower serum levels of LZM and IgM compared to the CK group. The SOD, CAT, and GSH-Px enzyme activities were significantly elevated in the livers of the nitrite-exposed group (<i>p</i> &lt; 0.05). The mRNA expression level of <i>Nrf2</i> was upregulated in the nitrite-exposed group, while <i>Keap1</i> was downregulated. The mRNA relative expression levels of <i>NF-κB</i>, <i>TLR-3</i>, and <i>TNF-α</i> in the immune pathway were upregulated in the nitrite-exposed group. The mRNA expression of the apoptosis gene <i>P53</i> was upregulated with increased nitrite concentration, along with the upregulation of the apoptosis-promoting gene <i>Bax</i> and the downregulation of the anti-apoptotic gene <i>Bcl2</i>. The mRNA expression of <i>Caspase 3</i> and <i>Caspase 9</i> genes in sea bass was significantly increased in the nitrite-exposed group (<i>p</i> &lt; 0.05). In conclusion, sea bass exposed to nitrite not only showed abnormal changes in serum composition but also showed oxidative stress, apoptosis, and liver tissue damage, highlighting the multifaceted impacts of nitrite exposure on aquatic biology.</p> Graphical Abstract <p>The graphical abstract of the nitrite-induced toxic effect in sea bass via liver and blood. ↑: increase, ↓: decrease.</p> <p></p>