Differential expression of cytochrome P450, aryl hydrocarbon receptor and metallothionein genes in croaker from the Gulf of Guinea, Ondo State, Nigeria

Coastal ecosystems along Nigeria's Gulf of Guinea face increasing pollution from industrial discharges and oil-related activities, posing serious threats to marine biodiversity. This study investigated detoxification gene expression cytochrome P450, aryl hydrocarbon receptor (AhR), and metallothionein (MT) in two sympatric croaker species, Pseudotolithus typus and Pseudotolithus elongatus, collected from Awoye, Ayetoro, and Idi-Ogba in Ondo State. Heavy metals and Polycyclic Aromatic Hydrocarbons (PAHs) were quantified in liver, gill, kidney, and muscle tissues, while gene expression was assessed using qPCR. Results revealed distinct spatial, seasonal, and tissue-specific bioaccumulation patterns, with higher contaminant loads during the dry season. The liver exhibited the highest total metal and PAH concentrations, followed by kidney, muscle, and gill tissues. P. elongatus accumulated higher contaminant levels than P. typus, particularly at Idi-Ogba, indicating greater anthropogenic influence. Gene expression analyses showed significant upregulation (p < 0.05) of AhR, cytochrome P450, and MT in liver and kidney tissues, correlating positively with contaminant concentrations. Regression models indicated strong associations between heavy metals and MT expression (R² = 0.999) and between PAHs and AhR/P450 expression (R² = 0.96-0.97). P. elongatus exhibited a stronger transcriptional response to organic pollutants, while P. typus responded more to metals, reflecting species-specific detoxification strategies. This study provides the first comparative molecular information into contaminant-induced stress in Pseudotolithus species, highlighting their potential as biomarkers for monitoring coastal pollution in the Gulf of Guinea.