Temperature tolerances and southern African distribution of a tropical freshwater shrimp Caridina nilotica (Decapoda: Atyidae)

Abstract

Laboratory estimates of median time of survival (MTS) were used as an index of the temperature tolerance of the warm water shrimp Caridina nilotica. Tolerance to high (≧30 °C) and low (≦10 °C) temperature was examined in seasonally acclimated shrimps from subtropical Lake Sibaya. The MTS decreased rapidly above 30 and below 10 °C. The MTS temperature response curve predicted a ‘range for activity' extending between 11 to 11,5 °C and 31,5 to 32 °C. This tolerance range broadly matches the span of environmental temperatures which shrimps are likely to experience within their geographical range, implying that distribution may be temperature related. The physiological restrictions implied by the anomalously low upper tolerance limit may be circumvented by avoidance behaviour (e.g. diel offshore migrations) in suitable habitats.