Evaluation of the toxicity of the pesticide acephate and his by-product methamidophos over the behaviour of zebrafish Danio rerio (Cypriniformes, Cyprinidae).

Abstract

Worldwide, Brazil leads in the use of pesticides, and acephate is the fifth most used pesticide in the country. This component and its by-product methamidophos, may cause deleterious effects on the physiology and behaviour of various animals when in contact with water. Studies investigating the negative impacts of acephate in animals have used zebrafish larvae as a model species, but the effect on adult individuals remains unclear. Our main objective was to assess the behavioural changes in adult zebrafish (Danio rerio) exposed to acephate and methamidophos. To this end, 160 individuals of zebrafish were divided in three groups: acephate, methamidophos (exposed) and control groups (non-exposed), where subjects on the treatment groups were exposed to 7 μg/L of acephate and 7 μg/L methamidophos for 28 days. To compare the groups, behavioural assessments were carried out using scan sampling with instantaneous recordings of behaviour every 30 seconds, for ten minutes each day. Fish behaviour and fish location in the water column were compared between treatment and controls using Generalized linear Mixed Models (GLMMs). The results showed alteration in swimming patterns, an increase in aggression, an increase in abnormal behaviours and other stress-related behaviours, such as gasping for air, provoked by acephate and methamidophos. Similarly, fish in the treatment group preferred to swim near the surface of the water. These behavioural alterations caused by acephate and methamidophos may have serious consequences to wild fish communities, such as an increased risk of predation and may contribute to the extinction of local populations. These findings highlight the usefulness of behaviour as a tool to assess environmental impact caused by pesticides.