Physiology effects of the insecticide cartap hydrochloride on silver barb (<i>Barbonymus gonionotus</i>)

Cartap hydrochloride (CH) is commonly used to control insect pests in the Mekong Delta, and this study assesses the effects of CH (1%, 10%, and 20% of the LC50-96-h value) on brain cholinesterase (ChE) activity, food intake, feed conversion rate and growth of silver barb (Barbonymus gonionotus, Bleeker, 1849) under laboratory conditions. The inhibition of the AChE activity increased with both concentration and time, reaching its peak 9 hours after exposure. After 96 hours, the inhibition remained at 10.4% in fish exposed to the lowest concentration and at 18.2% and 19.9% in fish exposed to the two highest concentrations. After 48 hours the fish was placed in clean water, but the inhibition levels at the two highest concentrations still remained at 20% until day seven, and only recovered fully after 14 days. The feed intake was similar between the control and all treatments, but the fish exposed to CH had higher feed conversion ratio than the fish in the control during the first 30 days. This indicates an increased stress in the exposed fish and that more energy was used for detoxification. As a result, the fish in the control had gained most in weight after 60 days, while fish exposed to the highest level of CH had gained the least, and there was a significant effect of CH on the fish growth. It is concluded that expected water levels of CH from doses commonly sprayed on rice fields may affect the health of fish in these habitats, and the use of CH should be limited, as it may impact negatively on the healthy fish production in the Mekong Delta.