The indiscriminate use of fertilizers has resulted in nutrient enrichment giving rise to eutrophic conditions in many freshwater bodies in Sri Lanka. Few studies have investigated effects of field levels of nitrate and phosphate on commercial freshwater species. The present study therefore attempted to assess the individual and synergistic effects of nitrate and phosphate on post larvae of the Giant fresh Water Prawn Macrobrachium rosenbergii, which are released in large quantities into reservoir systems of the dry zone of Sri Lanka.

Arsenic (As) and Cadmium (Cd) are two of the heavy metals that gained public and national attention of the Sri Lankan community. Globally, As and Cd are reported as two of the most toxic heavy metals that cause physiological and biochemical alterations and mortality in exposed organisms. Cadmium levels in the range of 0.001 to 0.138 mg l -1 have been reported in both ground and surface water sources of Sri Lanka. Few studies in the country have documented levels of arsenic in natural water bodies. Furthermore, studies assessing the potential toxicity of these two metals to species that are of importance to Sri Lanka, are scarce. The aim of this preliminary study was to investigate the effects of environmentally relevant levels of As and Cd on the commercially exploited fresh water prawn Macrobrachium rosenbergii, using its post larvae, which are initially released into reservoirs in Sri Lanka. Post larvae were collected from a culture facility in Pambala, Chilaw and were maintained in glass beakers. They were acclimatized before use for 96 hr acute toxicity trials, where they were exposed to a series of concentrations of either As (from 0.001 to 0.08 mg l -1 ) and Cd (from 0.001 to 0.05 mg l -1 ). Constant experimental conditions were maintained in both the control and treatment, each conducted in triplicate.