Behavioural Responses of the Freshwater Bivalve Lamellidens marginalis to Chronic Exposure to Lambda-Cyhalothrin, Imidacloprid and Their Binary Mixture

The presence of pesticides in freshwater habitat affects nontarget aquatic organisms. Freshwater bivalves are useful indicators of the impact of pesticides due to their continuous exposure to surrounding water. The current study aimed to investigate Lamellidens marginalis behavioural responses after LC (lambda-cyhalothrin), IMI (imidacloprid), and the binary mixture of LC+IMI chronic toxicity (21 d). There were four treatment groups (control, LC, IMI, and LC+IMI) (n=4) and observed for mucus secretion, valve gaping and closing, extension and withdrawal of the foot, and siphoning activity at 2, 4, 6, 12, and 24 h on Day 0, Day 1, and Day 3 (24 h). Observation was conducted at every day from Day 4 to Day 21. Lamellidens marginalis control mussels maintained normal behavioural activity throughout the study period. A significant deviation in normal behaviour and moderate mucus secretion was observed in LC, IMI treatments. The mucus secretion score was 0 for control treatment, 2 for both LC and IMI treated groups, and 3 for LC+IMI treatment. Moreover, LC+IMI resulted in long/complete closure of valves, strongly reduced foot movement, and impaired siphon function. In general, behavioural responses can be used as a reliable biomarker in L. marginalis exposed to LC and IMI.