Swimming activity responses to water current reversal support selective tidal-stream transport hypothesis in juvenile thinlip mullet Liza ramada
Abstract
Swimming activity of thinlip mullet Liza ramada in response to water current reversal was investigated experimentally. A total of 130 young of the year thinlip mullet ranging in size from 22 to 36 mm were entered in trials with four different conditions over three weeks. The fish were subjected to current reversal (6.2/6.2 h) and a LightDark cycle (12/12 h). Swimming direction (with or against the current) was videorecorded throughout the experiments. The mullet showed an effective synchronisation of their swimming activity to water current reversal and LightDark cycle. This synchronisation could demonstrate the existence of a diurnal selective tidal-stream transport in the natural environment as observed in the two other European catadromous species.