Ammonia Concentrations in Different Aquaculture Holding Tanks

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

Inhibition of excitatory amino acid-activated currents by trichloroethanol and trifluoroethanol in mouse hippocampal neurones

1. The effects of the active metabolite of chloral derivative sedative-hypnotic agents, 2,2,2-trichloroethanol (trichloroethanol), and its analog 2,2,2-trifluoroethanol (trifluoroethanol), were studied on ion current activated by the excitatory amino acids N-methyl-D-aspartate (NMDA) and kainate in mouse hippocampal neurones in culture using whole-cell patch-clamp recording. 2. Both trichloroethanol and trifluoroethanol inhibited excitatory amino acid-activated currents in a concentration-dependent manner. Trichloroethanol inhibited NMDA- and kainate-activated currents with IC(50) values of 6.4 and 12 mM, respectively, while trifluoroethanol inhibited NMDA- and kainate-activated currents with IC(50) values of 28 and 35 mM, respectively. 3. Both trichloroethanol and trifluoroethanol appeared to be able to inhibit excitatory amino acid-activated currents by 100 per cent. 4. Concentration-response analysis of NMDA- and kainate-activated current revealed that trichloro-ethanol decreased the maximal response to both agonists without significantly affecting their EC(50) values. 5. Both trichloroethanol and trifluoroethanol inhibited excitatory amino acid-activated currents more potently than did ethanol. The inhibitory potency of trichloroethanol and trifluoroethanol appears to be associated with their increased hydrophobicity. 6. The observation that trichloroethanol inhibits excitatory amino acid-activated currents at anaesthetic concentrations suggests that inhibition of excitatory amino acid receptors may contribute to the CNS depressant effects of chloral derivative sedative-hypnotic agents