The effect of algal concentration and initial density on the population growth of the estuarine cladocera. Diaphanosoma brachyrumLiévin, were evaluated in an indoor experiment. A 2x4 layout that included two algal concentrations (Chlorella vulgaris 1x106 and 3x106 cell/mL) and four inoculation densities (100, 200, 300 and 400 ind./L) were established.Diaphanosoma brachyrum were reared in 150 mL flasks containing 50 mL of algal medium at 23 ±1oC, under salinity of 10 and a photoperiod of 12 h L: 12 h D. The lag phase required to initiate continuous population growth following inoculation was shorter for D. brachyrum fed 1x106 cell/mL and inoculated at 300 or 400 ind./L than that for D. brachyrum fed 3x106 cell/mL and inoculated at 100 or 200 ind./L. However, D. brachyrum fed 3x106 cell/mL and inoculated at 100 or 200 ind./L exhibited longer periods of positive population growth. The maximum population densities were 5245 ± 370, 6700 ± 710, 7 390 ± 150 and 6 540 ± 70 ind./L for D. brachyrum fed 1x106 cell/mL and inoculated at 100, 200, 300 and 400 ind./L, respectively, and 15100 ± 445, 12780 ± 249, 11850 ± 171 and 16980 ± 327 ind./L for D. brachyrum fed 3x106 cell/mL and inoculated at 100, 200, 300 and 400 ind./L, respectively. The average daily increasing rates of population were 0.122 ± 0.012, 0.105 ± 0.014, 0.09 ± 0.013 and 0.080 ± 0.01 for D. brachyrum fed1x106 cell/mL and inoculated at densities of 100, 200, 300 or 400 ind./L, respectively, and 0.173 ± 0.015, 0.161 ± 0,013, 0,137 ± 0,014 and 0.116 ± 0.015 for D. brachyrum 3x106 cell/mL and inoculated at densities of 100, 200, 300 and 400 ind./mL, respectively. The result of the present experiment indicate that the algal concentration and inoculation density significantly affect population growth of D. brachyrum. Furthermore, the results suggest that the optimal algal concentration and inoculation density fort he mass culture of D. brachyrum should be 3x106 cell/mL and 100 ind./L.
