First Comprehensive Assessment of Cytochrome P4501A Response of Common Carp (Cyprinus Carpio, Linnaeus 1758) with the Nutrient Enrichment in Different Freshwater Lakes of North-Western Himalayas.

内容摘要

Cytochrome P4501A (CYP1A) is a widely used biomarker of environmental stress in fish, primarily associated with xenobiotic metabolism but also responsive to broader changes in water quality. This study provides a region-specific, field-based assessment of hepatic CYP1A responses in Cyprinus carpio in relation to nutrient enrichment across freshwater lakes of the North-Western Himalayas. Fish and water samples were collected monthly over two consecutive years from four lakes representing contrasting trophic conditions Viz Dal, Wular, Manasbal, and Nilnag along with laboratory-maintained control fish. Hepatic CYP1A concentrations were quantified, and concurrent measurements of total phosphorus, nitrate-nitrogen, ammonical nitrogen, dissolved oxygen, temperature, and pH were conducted.CYP1A levels showed pronounced spatial and seasonal variability, with significantly higher concentrations in fish from nutrient-enriched lakes, particularly Dal and Wular, compared to less impacted lakes and laboratory controls. These lakes were characterised by elevated nutrient concentrations and comparatively lower dissolved oxygen levels, reflecting eutrophic conditions. To appropriately address repeated monthly sampling and non-independence of observations, linear mixed-effects models were applied, incorporating lake and season as fixed effects and sampling event as a random effect. Model outputs indicated that total phosphorus and nitrate-nitrogen were significant predictors of CYP1A variation after accounting for seasonal and site-specific effects, whereas ammonical nitrogen showed no independent influence. The results suggest that nutrient enrichment indirectly modulates CYP1A expression through altered environmental conditions such as oxygen availability and metabolic stress rather than direct contaminant exposure alone. Overall, this study demonstrates the utility of CYP1A as an integrative biomarker of ecological stress under eutrophic conditions and highlights the importance of mixed-effects modelling in long-term freshwater biomonitoring.