Impact analysis of calcium hydroxide on the juveniles of the river prawn, <i>Macrobrachium macrobrachion</i>

Abstract

The use of inorganic chemicals to boost agro production has recently been extended to other environmental purposes. This study thus was carried out to assess the potential lethal impact of calcium hydroxide (Ca (OH)₂) on aquatic environment using the brackish river prawn as the indicator organism. The prawns were exposed to 0, 160, 320, 640, 1280, 2560 and 5120 mg/L of Ca (OH)₂ using static renewal bioassay for 96 hours under laboratory conditions. The bioassays were monitored throughout the exposure period and mortality occurred in some of the tanks at random. Results showed that low mortality rate was recorded in the experiment which was not high enough to extrapolate the median lethal concentration (LC₅₀). Deaths occurred in the control tank and tanks treated with 1280 mg/L and 2560 mg/L of Ca (OH)₂ while some prawns molted in few tanks during the test period. Analysis of variance and correlations were significant at P<0.05. There were no mortalities in the tanks with the highest concentration of 5120 mg/L. This implies that Ca (OH)₂ is generally of low toxicity to prawns and can be used as calcium supplement in prawn culture from the general observations made which is detailed in this paper.

Keywords: Calcium hydroxide, calcium supplement, prawn culture, toxicity bioassay