EFFECTS OF SALINITY ON ACUTE TOXICITY OF LEAD NITRATE TO LARVAL STAGES OF GIANT FRESH-WATER PRAWN, MACROBRACHIUM-ROSENBERGII (DEMAN)

An exploratory test for the acute toxicity of lead nitrate on early la rval stages of Macrobrachium rosenbergii was carried out at salinity 1 5 ppt in a static water system. The median lethal concentrations (LD50 ) of lead nitrate at 24, 48, 72 and 96 h were 35, 25, 15 and 1 ppm, re spectively. These median lethal concentrations were then used as start ing concentrations for determining combined effects of salinity and le ad nitrate on survival of 4-day-old larvae (larval stage II), 14 day-o ld larvae (larval stage V), and 24 day-old larvae (larval stage VIII) of M. rosenbergii. The combined test was run under similar conditions to the exploratory test but at different salinities (from 5 to 25 ppt) . For all stages of larvae, salinity showed a strong influence on larv al survival. At salinities closed to 15 ppt, the larvae were more tole rant to lead nitrate toxicity than at other salinities. Toxicity of le ad nitrate increased with increasing salinity and LD50 varied with lar val stages. The 14-day-old larvae were the most resistant to lead nitr ate.