The genome size of the abalone Haliotis midae was determined using flow cytometry and calculated relative to the known genome size of the rainbow trout (Oncorhynchus mykiss). The C value for H. midae was estimated to be 1.43 pg, which is smaller in comparison with other abalone species with the same number of chromosomes (2n = 36), namely H. corrugata, 2.14 pg; H. rufescens, 1.82 pg; and H. fulgens, 1.71 pg. In these Californian abalone species, a positive correlation between C value and the number of metacentric/submetacentric chromosomes with a subsequent loss of submetacentric/subtelocentric chromosomes was observed. Karyotypic analysis in H. midae indicates 6M 10SM 2 ST (metacentric submetacentric subtelocentric) chromosome pairs, the lowest number of metacentric and the highest number of subtelocentric chromosomes when compared with the Californian species. This pattern, in the light of recent phylogenetic and cytogenetic evidence, leads us to hypothesize that during the evolution of the genus, there were some preferential karyotypic rearrangements. Research on the genome size of other abalone species in general and specifically South African species, combined with chromosome banding techniques, could provide more insight into the evolution of this genus.