Genetic Studies on the Pacific Abalone—II: Excessive Homozygosity in Deficient Animals

Abstract

On the basis of observations of an excessive frequency of occurrence of homozygotes at the esterase F locus, an inbreeding structure was previously reported in the wild population of the Pacific abalone, Haliotis discus hannai Ino, in Iwate Prefecture. The occurrence of deficient or malnutritional animals, locally called “Rho-gai” or “Yase-gai” and of less commercial value, has long been known among fishermen. The relative weight of the soft parts of the body to the whole body weights made it possible to distinguish such deficient animals from normal ones. The deficient animals revealed a much higher frequency of homozygosity than that in normal animals. The results were interpreted as a reflection of an inbreeding structure called “inbreeding depression”. Additional supporting evidence indicated that the overdominance of heterozygotes observed at (he esterase M locus in normal animals was offset by the excessive homozygosity in deficient animals and turned to homozygote excess. On the basis of these observations, as well as the aging relations of fitness at the esterase M locus reported before, some general guidelines of selective breeding for increasing production and for genetic improvements of the Pacific abalone are suggested. © 1978, The Japanese Society of Fisheries Science. All rights reserved.