EFFECTS OF TEMPERATURE ON LIFE HISTORY STRATEGIES OF THREE STRAINS OF BRACHIONUS ANGULARIS GOSSE

Rotifers are valuable live food for larval fish and crustacean. Brachionus angularis is usual specie in fresh water, and is considered to have important status in material cycle and energy transportation in freshwater ecosystem,and applied in aquaculture.Determining optimal conditions for the rotifer population growth in an artificial environment necessitates the study on its life history strategies.The factors that are most likely to influence rotifer life history strategies are genotype (strain),food quality and quantity,and temperature,etc.Effects of strain and temperatrue on the life history strategies of B.angularis were investigated in the present study. By population accumulative culture,with Chlorella pyrenoidosa (at 6.0×106cells/mL)as the rotifer’s food,the effects of temperature on the population growth,body size,and egg size of three different strains of B.angularis, respectively from Qingdao,Guangzhou and Wuhu cities,were studied at 20℃,25℃ and 30℃. The results showed that temperature affected the population growth rate,body size,and egg size significantly.The optimum temperature of population growth of QD strain was 30℃,and that of GZ strain was 25℃;WH strain had 100%mortality at 30℃.The relationships between temperature and population growth rate of both QD and GZ strain were curvilinear:Y=0.0009X2-0.0061X+0.4090;Y=-0.0144X2+0.7412X-8.3751.Rotifer of GZ strain got its maximum population growth rate (1.1627d-1 )at the temperature 25.74℃. Both body size and egg size tended to decrease with the increasing temperature.In our experimental temperature range,the variation of body size was 42.90%in GZ strain,14.43%in QD strain,and 6.23%in WH strain. Strain also affected the body and egg size of rotifer significantly. Among the three strains,the body size of WH strain was the largest,and that of QD strain was the smallest. At 20℃and 25℃,the body size of WH strain was 74.91%and 87.98%larger than QD strain,respectively. Egg size tended to be smaller with the increasing temperature,and the variance between 20℃ and 30℃ of GZ strain was 22.50%.But the relative egg size tended to be larger with the increasing temperature.At 20℃and 25℃,WH strain had the largest egg size,but the relative egg size of WH strain was the smallest among the three strains.Egg size of QD strain was significantly smaller than GZ strain at both 20℃ and 25℃,and the variance of egg size between QD strain and WH strain was 44.01%and 37.49% at 20℃ and 25℃,respectively. Strain had a more important effect on the rotifer’s body and egg size than temperature.