Effects of Temperature on Population Growth and Resting Egg Production of Freshwater Rotifer (Brachionus calyciflorus)Effects of Temperature on Population Growth and Resting Egg Production of Freshwater Rotifer (Brachionus calyciflorus)

Resting egg production of rotifers provides critical advantages in larviculture of most fish species due to the reduction in the costs of labour and algae production. The study was conducted to investigate the effects of temperature on population growth and resting egg production of a freshwater rotifer, Brachionus calyciflorus, collected in Northern Vietnam. The rotifer was pre-cultured at 27ºC before being transferred to the cultures at 15 and 35ºC while the control was maintained at 27ºC. One-liter beakers filled with 500mL culture medium were used with three replicates for each temperature group. Stock rotifers were inoculated at an initial density of 200 ind ml-1 and fed with concentrated fresh algae. The results indicated that population growth rate (r) of rotifers cultured at 27 and 35ºC were significantly higher than that of rotifers at 15ºC while the highest density was attained from the treatment of 27ºC, at 608.3 ind mL-1, compared to 468.3 and 360.5 ind mL-1 at 35 and 15ºC, respectively. Transferring the cultures from 27 to 35ºC significantly increased the rate of resting egg carrying females with the maximum rate of 31.5% compared to 21.2 and 13.5% of the rotifers at 27 and 15ºC, respectively. The resting egg densities of the cultures at 35ºC were also significantly higher than those at 15 and 27ºC. The resting egg carrying females appeared and increased their rates in concurrence with increases in the population density. The present results are important information for resting egg induction and production of rotifer in larviculture.