Acute and chronic toxicity of Cypermethrin on juveniles of the non-target freshwater species Gambusia affinis: Impacts on morphometric traits and environmental stress biomarkers

Cypermethrin (CYP), a widely used synthetic pyrethroid insecticide, frequently contaminates aquatic ecosystems and may threaten non-target organisms such as fish. This study evaluated the acute and chronic toxicity of CYP in juvenile mosquitofish, Gambusia affinis (Baird and Girard, 1853) (Actinopterygii: Poeciliidae), by assessing morphometric parameters and environmental stress biomarkers. Juveniles were collected from a relatively unpolluted site, El Karma (Annaba, Algeria). Acute toxicity assays were conducted to determine the LC50/96 h, after which fish were exposed, and to determine the sublethal concentration (LC25) for 60 days under controlled laboratory conditions. Morphometric traits, including body length, head length, body weight, and head weight, were measured alongside biochemical biomarkers: acetylcholinesterase (AChE), glutathione S-transferase (GST), malondialdehyde (MDA), and total lipid content. The LC50/96 h and LC25/96 h values were 2.196 ng/L and 1.851 ng/L, respectively. Only chronic exposure induced increased body size and weight compared with controls. Biochemical analyses revealed AChE inhibition, enhanced GST activity, elevated MDA levels, and reduced lipid content, indicating oxidative stress, lipid peroxidation, and activation of detoxification pathways. These findings demonstrate that CYP induces both physiological and biochemical alterations in G. affinis, highlighting the value of combining growth-related and biomarker-based approaches for assessing pesticide toxicity in aquatic ecosystems.