Extended Photoperiod Exposure Affects Imidacloprid Toxicity on Juvenile Crayfish Procambarus clarkii by Regulating Oxidative Stress and Neuroendocrine Pathways

Imidacloprid (IMI), a neonicotinoid insecticide, is widely recognized for its environmental persistence and toxicity to non-target aquatic organisms. Extended photoperiod exposure (EPE), an emerging anthropogenic stressor, further disrupts aquatic ecosystems by altering physiological and biological processes. However, their combined impacts on aquatic species remain insufficiently explored. This study evaluates the synergistic effects of IMI and EPE on Procambarus clarkii, an ecologically and economically significant crayfish species. Crayfish were exposed to 25 µg/L IMI under normal photoperiod (1000 lx, L:D = 12:12 h) and additional intensified and extended photoperiod (5000 lx, L:D = 18:6 h) treatments over one month. Key parameters, including survival rate, growth performance, oxidative stress markers, immune enzyme activities, neuroendocrine hormone levels, and gene expression, were assessed. The results indicate that EPE significantly amplifies the adverse effects of IMI. EPE reduced survival rates and growth performance, particularly in the 5000 lx group. IMI combined with EPE markedly elevated oxidative stress, as evidenced by increased malondialdehyde (MDA) levels and altered activities of superoxide dismutase (SOD) and catalase (CAT). Immune functions were impaired, with significant reductions in lysozyme (LZM) and acid phosphatase (ACP). Neuroendocrine disruption was observed through suppressed melatonin (MT) levels under EPE. Gene-expression analysis revealed upregulation of oxidative stress and apoptotic pathways (Cu/Zn-SOD, CAT and caspase-3) and downregulation of anti-apoptotic genes (bcl-2) and molt-inhibiting hormone (MIH). This study demonstrates that EPE exacerbates IMI-induced physiological and biochemical disruptions in P. clarkii. The findings highlight the pressing need for integrated management strategies addressing chemical and light pollution to protect aquatic ecosystems and sustain economically important species like crayfish.