HABITAT PREFERENCE AND POPULATION-STRUCTURE OF THE ROCK CATFISH (AUSTROGLANIS-SCLATERI) IN THE SENQUNYANE RIVER, LESOTHO

Four surveys were conducted in the Senqunyane River between August 199 5 and February 1996. Austroglanis sclateri specimens were collected by means of electro-fishing and gill netting. In relation to other studi es relatively large numbers of individuals (86) were sampled and the h abitat for each individual was documented. The population was divided into different functional groups and habitat preference was expressed in terms of each functional group. It was evident that recruits (small est functional group) preferred backwater pools as opposed to the larg er fish, which preferred stickles and runs. The preferred bottom subst rate was cobbles in the case of the recruits and rubble for the older groups. The mean preferred water depth for this species ranged between 19 and 59 cm. Recruits were mostly sampled at slow current velocities (< 0.1 m/s) while the other functional groups preferred faster curren t velocities with mean values being 0.44 and 0.42 m/s respectively. Th e baseline information regarding habitat preference is important for d etermining instream flow requirements. A. sclateri would probably not do well in impoundments as it was found that more than 90% of specimen s larger than 4.5 cm (standard length) were found within current veloc ities exceeding 0.14 m/s and no specimens were collected at depths gre ater than 1.5 m.