In the seawater control, the behaviour of L. branchialis before and after the water was replaced in the arena was not significantly different (P >0·05 for all parameters) and consequently the **data** were grouped together to define normal behaviour. Mean distance travelled was 31·1 ± 23·4 cm in 3 min with a velocity of 1·74 ± 1·31 cm s − 1 . A high turn rate of 71·62 ± 46·7 degrees s − 1 was observed, resulting in a number of relatively complex path shapes, giving a mean fractal dimension of 1·38 ± 0·31.