Ammonia Concentrations in Different Aquaculture Holding Tanks

Abstract

Ammonia was measured in collapsible pond, concrete tank, and earthen pond of the same size, volume and containing same fish biomass cultured under intensive system. Ammonia was also evaluated from a natural pond under extensive culture. Ammonia was measured in the afternoons for 12 weeks using Nessler method. Temperature and pH were measured in situ using Portable tester. Unionized ammonia was calculated from total ammonia using spreadsheet computation. Result showed total ammonia ranging from 1.4 to 10 mg/l with highest concentration recorded in collapsible pond and lowest found in natural pond. The unionized ammonia concentrations followed the same pattern with concentrations ranging from 0.002 to 1.13 mg/l. The trend in the total ammonia and unionized ammonia concentrations is: collapsible pond > concrete tank > earthen pond > natural pond. Temperature and pH ranged between 29.1 to 35.9 °C and 6.35 to 8.03 respectively, with the highest temperature and pH recorded in the collapsible pond and lowest temperature and pH found in natural pond. Temperature and pH followed seasonal pattern with lowest and highest temperatures and pH recorded at the end of rainy season and in the dry season respectively. High unionized ammonia recorded in the collapsible and concrete ponds was from excretion of high protein rich feed, decomposition of uneaten feed, high stocking density, low water exchange rates, water source and the alkaline medium of the systems. Low unionized ammonia in earthen pond and natural pond was attributed to the presence of phytoplankton, high water exchanges, feeding system, low acidity and relatively low temperature. Remediating measures such as the use of biofilters, aeration and reduction in feeding, temperature and pH should be employed to reduce the high concentration of unionized ammonia.