The size variation of rotifer <i>Brachionus rotundiformis</i> cultivated with different feed at 40 ppt salinity

Rotifer <i>Brachionus rotundiformis</i> is a group of zooplankton which is used by fish larvae for feeding to initiate their growth. This zooplankton is widely favored by marine fauna larvae because of its small size can fits well with various larval mouth; thus, it is easily preyed by larvae. This study aimed to determine the variation of rotifer <i>B. rotundiformis</i> morphometry if cultured with different feed at 40 ppt. The use of 40 ppt salinity is expected to provide a variable morphometric size because <i>B. rotundiformis</i> has a polymorphism property. Microalgae used as feed for rotifer <i>B. rotundiformis</i> were <i>Prochloron</i> sp. and <i>Nanochloropsis oculate</i>. Microalgae were cultured with Hirata medium. In the early stages, <i>B. rotundiformis</i> was cultured at optimum temperature (28 ºC) and salinity 20 ppt, then it was cultured at salinity 40 ppt. Salinity adaptation was done by raising the salinity of the medium by 2 ppt every two days in a 10 ml reaction tube containing 10 individuals. After adaptation, <i>B. rotundiformis</i> was transferred in a 1000 ml container with a density of 50 individuals. For the morphometric aspect, the total length, the length of the lorica, the width of the lorica and the anterior width were measured. The result showed the morphometric of rotifer <i>B. rotundiformis</i> fed with microalgae i>Prochloron</i> sp. at 40 ppt salinity was smaller than that of the rotifer fed with <i>N. oculate</i>. Based on that finding it can be concluded that <i>B. rotundiformis</i> fed with <i>Prochloron</i> sp. at a salinity of 40 ppt has the potential to be developed as feed for fish larvae. Further investigations on how to accelerate the cultivation of microalgae <i>Prochloron</i> sp. as feeding for <i>B. rotundiformis</i> are needed.