Clonal composition of Brachionus plicatilis s.s. and B. sp. ‘Austria’ hatchery strains based on microsatellite data

The recent application of different molecular techniques to Brachionus plicatilis hatchery strains has revealed the presence of five members of what is now known as the B. plicatilis complex of cryptic species and has offered new perspectives to the aquaculture industry via a genetically-oriented strain management. In this work, we have employed the high versatility of microsatellites to increase the resolution of previous genetic analyses and study the clonal composition of two of the rotifer species found in hatcheries, namely the B. plicatilis s.s. and B. sp. ‘Austria’. A total of 69 B. plicatilis s.s. and 78 B. sp. ‘Austria’ individual rotifers from 13 hatchery strains were genotyped at seven and three microsatellite loci, respectively. Wild population samples and laboratory clones were used as reference material. Sample relationships were inferred using genetic distance estimates from the allele frequencies of the resulted genotypes. A notably low clonal diversity was found in hatcheries. Some of the strains were actually clonal cultures. In many cases, rotifers with the same multilocus genotype were present in two or three different strains. Interestingly, most B. sp. ‘Austria’ rotifers found in hatcheries have significant genetic similarities. Overall, our results indicate that hatcheries exploit a very small fraction of the available Brachionus genetic diversity even at the intra-specific level. Rotifer circulation practices seem to be a major cause for this outcome. There is a growing evidence that the aquaculture industry could benefit from the use of new Brachionus clones and/or species.