Changes in the swimming activity and the glutathione S-transferase activity of Jenynsia multidentata fed with microcystin-RR.

We report the effects of sublethal doses of microcystin-RR (MC-RR) on the swimming activity of Jenynsia multidentata as well as the simultaneous response of its detoxication system by measuring glutathion S-transferase (GST) activities in the liver and brain of fish. MC-RR was applied on the food pellets at doses of 0.01, 0.1 and 1 microg g(-1). Swimming activity was recorded 10 min each hour over 24h by using a computer-based image processing system, which facilitates quantification of two measures of fish swimming behaviour (average velocity, movement percentage). Results show that low levels of cyanotoxin increased the swimming activity, while the highest dose used produced significant changes with respect to control group only since approximately 20 h of exposure, when the swimming activity was decreased. On the other hand, GST activity was significantly increased only in the liver and brain of fish fed with the highest MC-RR dose. Both results suggest that fish are reacting to the stress caused by low doses of MC-RR by increasing their swimming activity, raising further questions on the probable neurotoxicity of MCs, and presenting the behavioural change as a good biomarker of early toxic stress. On the other hand, fish reduced their swimming speed at the highest MC-RR dose, when the detoxication activity began, which can be hypothesized to be a reallocation of their energy, favouring detoxication over swimming activity.