Population stagnant growth caused by cryptic species of Brachionus plicatilis species complex

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Rotifer Brachionus plicatilis has been an indispensable zooplankton as a live-food in aquaculture since 1960s. Three types of L, S and SS have been recognized based on their body size, but recent studies revealed that B. plicatilis consists of genetically-isolated species/strains, called species complex. Based on substitutions in the COI locus, the specimens examined in this study were classified into 5 genetically-isolated strains. Subsequently, the two strains of the L-type, Amami and Obama strain, were further investigated to compare their life-history parameters. The Amami strain showed relatively faster growth and maturation, but had lower stavation resistance than the Obama strain. These differences in their life-history suggested that the Amami and Obama strains could be considered to be r-and K-strategists, respectively. Such different adaptive behaviors between the two strains can cause the competition in the mass-culture, and resulted in the stagnant growth or even collapse of the population.