A multi-biomarker assessment of chronic effects of an insecticide Acer 35 EC on Nile Tilapia Oreochromis niloticus under laboratory conditions
Résumé
Acer 35EC is an insecticide (20 g/L lambda-cyhalothrin + 15 g/L acetamipride) widely used in pest control in many West African countries, and particularly in cotton culture in north Benin. This study aimed to investigate under laboratory conditions the chronic effects of Acer 35EC on Nile tilapia Oreochromis niloticus using a multi-biomarker approach. For this purpose, juveniles of Nile tilapia were exposed to sublethal concentrations of Acer 35 EC (0, 1 and 10% of LC50- 96 h value) in glass aquariums during 56 days. After 0, 28 and 56 days of exposure, several biomarkers including enzymatic activities (indicators of detoxification and oxidative stress, neurotoxicity and immune responses) sex steroid hormones (Testosterone, Estradiol-17β and 11-Keto-testosterone) and histological alterations of liver, kidney and gonads were measured in males and females. A biomarker index (BI) was calculated based on the Integrated Biological Responses (IBR) developed by Beliaeff and Burgeot (2002). The results showed that Acer 35EC reduced cholinesterase activity in muscle of treated fish of both sexes. Females displayed high levels of testosterone and 11-Keto-testosterone after 56 days of exposure. Regarding immune biomarkers, intracellular superoxide anion production decreased in both sexes after 56 days of exposure. Oxidative stress biomarkers were not influenced by Acer-35EC exposure, regardless of sex and concentration. However, liver of females exposed to 1 and 10% of LC50- 96 h value was significantly (p < 0.05) affected after 28 and 56 days of exposure, while no histological differences were recorded in kidney between control and exposed fish. After 28 and 56 days of exposure, significant differences in the ovarian development were observed as the diameter of vitellogenic oocytes in exposed females differed from the one of the control females, indicating an increase in oocyte growth during the 1st month of exposure to Acer-35EC, followed by a regression during the 2nd exposure period. No differences were recorded in male gonads. Based on a large set of biomarkers, the insecticide Acer-35EC seems to impair different physiological functions in Nile tilapia juveniles on a time-dependent manner, with a stronger impact on females than in males.