DIURNAL DISTRIBUTION PATTERNS OF 0-BARBUS IN 2 DIFFERENT TYPES OF HABITATS IN THE RIVER SIEG, GERMANY( BARBEL BARBUS)

Diurnal distribution patterns of 0+barbel were examined in two differe nt types of habitats in the River Sieg (Germany) over a three month pe riod in the summer of 1994. 0+ fish were collected monthly from a bay and riffle using Point Abundance Sampling by electrofishing. Samples w ere taken along horizontal transects from the shoreline at intervals o f three hours over three 12 h periods. At each sampling point, environ mental variables were measured. In the bay, a temperature and oxygen g radient developed during the sampling period. The distribution of the larval and juvenile barbel (as well as other species) followed this gr adient. The habitat type ''riffle'' was characterised by the absence o f either temperature and an oxygen gradient. In June, larvae were caug ht exclusively near the shoreline, where lowest velocities occurred. I n July and August, juveniles had dispersed over the entire width of th e riffle. In contrast to the habitat type ''bay'' no diurnal movement could be observed.