Effect of food densities of two kinds of algae on body size and egg size in a growing population of the rotifer Brachionus calyciflorus of Anzali wetland

In many aquaculture operations where selected rotifer species are mass cultured for feeding fish larvae; it is considered highly desirable to provide the optimal prey size for maximizing larval survival and growth selection. A suitable strain and manipulation of culture conditions (algae food quality and quantity, temperature and salinity) are two possible approaches towards this goal. Laboratory population of the rotifer Brachionus calyciflorus were grown with two green algae (Chlorella sp. & Scenedesmus obliquus) at different food densities (0.1, 1, 10×106 cell/ml). The body size (lorica area) of individual rotifers and the size of eggs borne by them were measured at k-phase of population growth. The body size of rotifers fed Scenedesmus obliquus was larger with compared those fed Chlorella sp. The body size of rotifers fed higher food level (10×106 cell/ml) of Chlorella sp. significantly larger than those fed lower and medium levels(0.1, 1 ×106 cell/ml). Rotifers fed Scenedesmus obliqqus at 1×106 and 10×106 cell/ml density grew to a significantly large size(p<0.05) than fed at 0.1×106 cell/ml density. The size of eggs produced by adult females significantly larger at higher food level of both Chlorella and Scenedesmus. A significantly positive correlation was also observed between the adult body size and the size of egg produced.