THE EFFECT OF PH ON BRACHIONUS-CALYCIFLORUS PALLAS (ROTIFERA)

Cohorts of the rotifer Brachionus calyciflorus were grown in media with pH of between 2.5 and 11.5 in increments of 1 unit. pH was shown to exert a major influence on the growth rate and reproductive capacity of the B. calyciflorus. At pH 2.5 the B. calyciflorus showed a negative capacity for population increase (r(c)). The r(c) values of the cohorts reared at pH 3.5 and 4.5 were positive and these cohorts showed high net reproductive rates (R0). The r(c)'s of cohorts reared at pH of 5.5 and 6.5 were negative, while those of cohorts reared at pH 7.5 to 10.5 were positive with a peak in the R0 and cohort generation time (T(c)) at pH 8.5 and 9.5. Total mortality occurred in less that 24 h at pH 11.5. Successive generations of the progeny from the cohort held at pH 3.5 were reared under the same conditions. Although the r(c) of the F1 and F2 cohorts increased, the organism was unable to maintain the increased population growth rate, and the F4 generation showed an r(c) of almost 0.