Effects of turbidity on survival, osmoregulation and gill Na+-K+ ATPase in juvenile shrimp Penaeus japonicus

Abstract

Penaeus japonicus juveniles were exposed for 3 wk to different turbidities of suspended sediments: control [2 + 2 nephelometric turbidity units (NTU)], medium turbidity (35 f 15 NTU) and high turbidity (65 f 15 NTU). The mortality rate increased after exposure to high turbidity Exposed late luveniles became less tolerant to changes in ambient salinity and showed hlgher mortalities at low salinity. The effect on osmoregulatory capacity of shrimps was examined by determining the osmotic gradient between the haemolymph and the external medium in concentrated seawater (42 9& S) and in dilute seawater (15 O/m S). In young juveniles, osmoregulatory capaclty was generally not affected by turbidity. In late juveniles, it was sign~ficantly reduced by turbidity. Reduced osmoregulatory capacity resulted from impaired regulation of Na' and Clconcentrations. Gill Na+-K' ATPase activity of exposed late juveniles increased with turb~dity, apparently as a compensating reaction to the disruption of osmotic and ionic balance.