nanoelements, algae growth, fish aquarium, fisheries
Fish industry suffers millions of dollars by contaminated water and its effect on fish food. It is necessary to investigate the role of nanoelements in the microflora in water. Microalgae Chlorella fusca ACOI 621, Chlorella vulgaris ACOI 879, Scenedesmus acutus ACOI 538 and Scenedesmus obliquus ACOI 550, all native in fish ponds, were characterized in terms of specific growth rate. The effect of pH and the presence of Cr(VI) in concentrations up to 25 mg l-1 (50 mg l-1 for Chlorella fusca) has been evaluated. The logistic equation of population growth adequately describes the cellular growth. Experiments at pH = 6.5 and temperature around 24.5oC, in the absence of Cr(VI), led to specific growth rates () of 0.0370, 0.0284, 0.0359 and 0.0162 h-1 and maximum biomass concentrations (K) of 403.3, 369.2, 542.9 and 604.1 mg l-1 for C. fusca, C. vulgaris, S. acutus and S. obliquus, respectively. Experiments carried out with the same algae at approximately 21oC, also in the absence of Cr(VI), gave values of 0.0241, 0.0357, 0.0272 and 0.0289 h-1 and K values of 292.6, 169.9, 263.1 and 327.8 mg l-1 for initial pH = 6.5 and values of 0.0115, 0.0177, 0.0137 and 0.0158 h-1 and K values of 35.9, 3.0, 32.8 and 54.7 mg l-1 for initial pH = 7.9. Higher pH results in a significantly lower growth rate and C. vulgaris were less resistant microalgae to changes in the environmental conditions. Looking simultaneously at and K values, the best performance in terms of growth kinetics was obtained for S. acutus and C. fusca. Growth inhibition is visible for Cr(VI) 5 mg l-1 but concentrations up to 1 mg l-1 seem not to seriously affect algal growth, even increasing the C. fusca specific growth rate. For Cr(VI) < 1 mg l-1, varies between 0.08 and 0.17 h-1, depending on the algal species. The growth of C. vulgaris is severely inhibited by Cr(VI) = 5 mg l-1. The production of metabolites was small compared with biomass production, for all Cr(VI) concentrations. The organic carbon content of algae was about 40%-50% (dry basis), except for S. obliquus (around 30%). The biomass of C. fusca and S. acutus presents the greatest sedimentation rates. The presence of high Cr(VI) concentrations negatively affects the sedimentation.