Swimming Response to Water Current in Paratya Australiensis Kemp, 1917 (Decapoda,Atyidae) Under Laboratory Conditions

Abstract

The swimming response to flow of the freshwater shrimp Paratya australiensis Kemp, 1917, was examined in a small recirculating laboratory stream. On three occasions during 1993 larvae, juveniles, small and large adults, and ovigerous females were collected from headwater populations and tested in the laboratory at current speeds of 10 and 30 cm s-1. Juvenile and adult shrimps showed the same strong positive rheotactic response at velocities of 10 and 30 cm s-1. However, large adults moved upstream more rapidly than juveniles and small adults. This response was not influenced by the time of year of collection or time of day tested (day/night). Ovigerous females showed a weak response to flow and tended to maintain position rather than move into the current. Early stage larvae (stages III and IV) were not able to maintain position at the lowest velocities. The positive rheotactic response of shrimps, particularly large adults, is seen as an adaptation to compensate for downstream movement of larvae by drift and juvenile and adult displacement during high discharge events.